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THE MANUFACTURE OF
ORGANIC DYESTUFFS
THE MANUFACTURE OF
ORGANIC DYESTUFFS
AUTHORISED TRANSLATION, WITH ADDITIONS,
FROM THE FRENCH OF
ANDES WAHL, D.esSc.
PROFESSOR OF INDUSTRIAL CHEMISTRY IS THE UNIVERSITY OF NANCY
BY
F. W. ATACK
M.Sc. TECH. (MANC.), Ki5c. (Lttm), A.I.C.
DEMONSTRATOR IN TUB CHEMICAL LABOR \TORIES OF THE SCHOOL OF
TECHNOLOOY. UNIVERSITY OF MANCHESTER
WITH A PREFACE TO THK KNGL1SH EDITION BY
EDMUND KNECHT
PH.D. (ZiiRicii), F.I.C., M.Sc. TECH.
PROFESSOR OF TECHNOLOGICAL CHEMISTRY IN THK UNIVERSITY OF MANCHESTEB
LONDON
G. BELL AND SONS, LTD.
1919
First published 1914.
Reprinted 1918, 1919.
GLASGOW: PUINTKD AT TUB UMVEKHITY I-KKHS
BY ROBERT MACLKHOSE AND CO. LTD.
PREFACE.
AFTER the second edition of Benedikt's Chemistry of
the Coal-tar Colours had gone out of print, the only
other text-book on the subject which appeared in the
English language was Collin and Richardson's transla-
lation of Nietzki's Chemistry of the Organic Dyestujfs.
Both these works are now hopelessly out of date, and
would have to be entirely rewritten to be of any use.
The excellent works of A. G. Green (Tabular Survey)
and of Cain and Thorpe (Synthetic Dyestuffs) are rather
too compendious and expensive as class-books, and
there has been for some years a demand for a really
reliable text-book for the use of students, and also for
others who merely wish to obtain a general idea of the
subject. When Dr. Wahl's work, ^Industrie des
mati&rea colorantes organiquvs, appeared as one of the
numerous volumes of Deromes's Bibliothbque des
indiistries chimiques, I was at once convinced that
this excellent little book, written by a chemist who is
a recognised authority, and has also had considerable
practical experience, would constitute a worthy suc-
cessor to that of Benetlikt, and would supply a real
want. I therefore suggested to Mr. Atack that he
should undertake the translation, and, when he com-
municated this to the author, Dr. Wahl not only gave
his immediate consent, but undertook to collaborate in
bringing the English edition up to date. Much new
matter has been added as a consequence of the rapid
development of this industry from a commercial as
well as from a theoretical point of view during the
comparatively short time that has elapsed between
vi PREFACE
the issue of the French and the English editions. The
writer has also taken some personal interest in the
publication in reading the proof-sheets and making
certain suggestions.
In two points the new book differs materially from
that of Benedikt. In the first place, practically no
attempt is made to educate the reader in organic
chemistry up to the point of his being able to com-
prehend the intricate chemistry of the dyestuffs. It
should therefore be clearly understood that anyone
seeking to derive any benefit from the book must of
necessity possess a good knowledge of ^organic
chemistry. In the second place, the application of
the dyestuffs is very superficially dealt with, and for
information on this point other books or manuals must
be consulted. While keeping the subject-matter within
the compass of a text-book, it has thus been possible
to introduce considerably more matter directly con-
cerned with the history, chemistry and manufacture
of the colouring matters than was the case with
Benedikt's textbook.
The work is not intended as a compendium. It
deals concisely with raw products, intermediate pro-
ducts, and finished dyestuffs in sufficient detail to give
the reader a complete survey of the subject. In most
cases the chapters contain short historical accounts of
great interest, and numerous reliable examples taken
from practice are introduced. It is obviously im-
possible to detail in a volume of this size the thousand
and odd colouring matters on the market, but the
examples given are typical of the groups, and repre-
sent the most important individuals, or those which
are best suited for illustration purposes.
EDMUND KNECHT.
FACULTY OF TECHNOLOGY,
UNIVERSITY OF MANCHESTER,
September, 1914.
CONTENTS.
TAGS
PREFACE BY PROFESSOR KNECIIT v
ABBREVIATIONS .... x i
LIST OF PRINCIPAL FIRMS ...... x iii
INTRODUCTION ........ 1
FIRST PART.
RAW MATERIALS.
01IAPTKR
I. COAL-TAR 7
Diagram of the Products obtained by the Dis-
tillation of Coal-Tar.
II. HYDROCARBONS 13
Benzene. Toluene. Xylenos. Cumenes. Com-
mercial Benzols. Naphthalene. Anthracene.
Phenan threne .
III. THE PHENOLS 19
Phenol. Crosols.
SECOND PART.
INTERMEDIATE PRODUCTS.
IV. SULPHONATflON 22
Constitution of Sulphonio Acids. Practical
details of Sulphonation. Apparatus. Sul-
phonic acids of Benzene, Toluene, -Naphthalene,
Phenols.
viii CONTENTS
CHAPTER PAQB
V. ALKALINE FUSION 33
Practical details. Phenols derived from Ben-
zone and Naphthalene. Naphthol sulphonic
acids.
VI. NITRATION 43
Practical details of Nitration. Nitro-dorivtt-
tivos of the hydrocarbons : Nitrobenzene,
Dinitro benzene, Nitro toluenes, Nitronaphtha-
lenes, Nitrophenols. Nitrosulphonic acids.
VII. REDUCTION OF NITRO-COMPOUNDS 53
Reducing agents. Electrolytic Reduction.
Primary amines : Aniline, Toluidines, Xylidines.
Diamines. Naphthylamines. Sulphonated
derivatives of the amines. Hydroxy-derivatives
of the amines. Sulphonated hydroxy-dorivatives
of the amines. Amidonaphthol sulphonic acids.
Nitro-derivatives of the amines.
VIII. ALKYLATION 68
Alkylation of the phenols. Alkylation of the
amines. Secondary amines ; Monomethyl- and
monoethyl- aniline, Benzylaniline, Diphenylani-
line. Tertiary amines ; Dimethylaniline, ethyl-
benzylaniline. Alkylamidophenols.
THIRD PART.
THE ORGANIC DYESTUFFS.
IX. CLASSIFICATION AND APPLICATION OF DYESTUFFS 74
Chromophores, Chromogens. Leuco-
compounds. Dyeing. Auxpchromes.
Quinonoid theory of Dyestuffs.
X. NITRO -DYESTUFFS 85
Picric acid. Martius yellow. Naphthol yellow S.
Constitution of Nitro-Dyestuffs.
XI. NITROSO-DYESTUFFS OR QUINONE-OXIMES - 01
Dinitrosoresorcinol. Nitrosonaphlhols.
XII. AZO-DYESTUFFS 91
Historical. Preparation. Classification.
Monoazo-dyestuffa : Hydroxyazo-compounds.
Amidoazo- compounds. Rules for the coupling
CONTENTS ix
CHAPTER PAGE
of diazo-compounds with Naphthols, Naphthyl-
amines, and their sulphonic acids. Mordant
Monoazo-dyestuffs. Pigment colours,
Diaazo-dyestuJJs : Primary. Secondary, sym-
metrical and unsymrnetrical .
Trisazo-dyestuffa .
XIII. HYDRAZONES 129
Relation to Azo-compoimds. Tartrazine.
XIV. STILBENE DYESTUFFS 133
Direct yellow. Mikado colours.
XV. DlPHENYLMETHANE DYESTUFFS - - - 137
Auramine.
XVI. TRIPHENYLMETHANE DYESTUFFS - - 142
Amido-derivatives.
Diamido-derivat-ives. Malachite green and its
substitution products. Patent blue.
Triamido-derivatives. Historical. Consti-
tution of Magenta. Manufacture of Magenta.
Properties of the Magenta series. Alkylated
derivatives : Methyl violet, Crystal violet,
Aniline blue.
Hydroxy-derivatives. Historical. Aurine.
Rosolic acid. Phenolphthalem.
XVII. XANTHENE DYESTUFFS 181
Pyronines . Pheny Ixan t hene. Rosamine .
Phthalelns. Fluorescem. Eosines. Galleme.
Rhodamines. Anisolines.
XVIII. AORIDINE DYESTUFFS 195
Acridino yellow. Chrysaniline. Phosphine.
XIX. ANTHRACENE DYESTUFFS 200
Oxyanthraquinones. Alizarin, its constitu-
tion, manufacture and properties. Isomers of
Alizarin. Trioxyanthraquinones. Polyoxy-
anthraquinones.
Amido- and Hydroryamido-anthraquinoncs.
Anthraquinone derivative* containing a ftirthtr
group. Alizarin blue. Alizarin green.
Vat dyestuffs derived from Anthracene.
Indanthrene. Flavanthrene. Algol colours.
x CONTENTS
CHAPTER
XX. QUINONE-IMIDE DYESTUFFS -
Indamines.
Indophenols.
Thiazines : Amido-Thiazines. Thiazones.
Oxazines : Amido-Oxazines. Oxazones.
Azines : Eurhodines. *Eurhodoles.
Safranines. Safranoles. Mauveines. Indulines.
XXI. INDIGO AND INDIGOID DYESTUFFS - - - 266
Historical. Manufacture of natural Indigo.
Properties and constitution of Indigotine.
Syntheses of Indigotine. Indirubine. Indigoid
dyestuffs : Thioindigo, Ciba dyestuffs, Holindone
dyes tuffs.
XXII. THIAZOL DYESTUFFS 298
Primuline. Manufacture and derivatives of
Dehydrothiotoluidine.
XXIII. SULPHUR DYESTUFFS ------ 304
Trade Names. Manufacture. Constitution.
Classification.
Sulphtirised Vat Dyestuffs.
XXIV. ANILINE BI.ACK 317
Modes of formation. Constitution.
BOOKS OF REFERENCE 325
INDEX 329
ABBREVIATIONS.
(The date given is the first year of publication.)
Ann. Liebig's Annalen der Chemie. Leipzig. 1832.
Four volumes per annum.
Ber. Berichte der deutschen chemischen Gesellschaft.
Berlin. 1868.
Bull. Soc. chim. Bulletin de la Societe chimique de
France. Masson, Paris. Two volumes per annum .
1864. 4th series, 1907.
Bull. Soc. ind. Mulhouse. Bulletin de la Societe indus-
trielle de Mulhouse. Bader, Mulhouse. 1831.
B.F. Brevet frangais. (French patent.)
Chem.-Ztg. Cheniiker-Zeituiig. Cothen. 1887.
Chem. Ind. Chemische Industrie. Berlin.
Cornel. Rend. Comptes-rendus de TAcademie des
Sciences. Gauthier-Villars, Paris. 1835.
D.R.P. Deutsches Reichs Patent. (German Patent.)
Dingier. Dingler's polytechnisches Journal. Augsburg.
E.P. English Patent.
F. Friedlander, " Fortschritte der Teerfarbenfabrika-
tion."
Farb.-Ztg. Farber-Zeitung. Springer, Berlin. 1890.
J.C.S. Transactions of the Chemical Society. London.
1848. Two volumes per annum.
Journ. f. prakt. Chem. Journal fur praktische Chemie.
1834.
J, Soc. Chem. Ind. Journal of the Society of Chemical
Industry. London. 1882.
xii ABBREVIATIONS
Journ. Soc. Dyers and Col. Journal of the Society of
Dyers and Colourists. Bradford. 1885.
Monatsh. /. Ghent. Monatshefte fur Chemie. Vienna.
1880.
Mon. sci. Montieur scientifique. Dr. Quesneville, Paris.
1857.
Rec. trav. ch. P.-B. Recueil des travaux chimiques des
Pays-Bas.
Zeilsch.angew. Chem. Zeitschrift fiir angewandte Chemie.
Leipzig. 1888.
Zeitsch. f. Farben- und Textilchemie. Zeitschrift fiir
Farben- und Textil-Chemie. Dr. Buntrock.
Vieweg, Braunschweig. 1892.
LIST OF PRINCIPAL FIRMS.
[A.] Aktiengesellschaft fur Anilinfabrikation, Berlin.
(Berlin Aniline Co.)
[B.A.S.F.] Badische Anilin- und Soda-Fabrik, Ludwigs-
hafen a/Rhein. (Badische Co.)
British Alizarine Co., London.
Easier chemische Fabrik, Basle.
Brooke, Simpson and Spiller, Hackney Wick,
London, E.*
[By.] Farbenfabriken vorm. Bayer & Co., Elberfeld.
(Bayer Co.)
[C.] Cassella & Co., Frankfurt a/Main.
Chemische Fabriken Griesheim Elektron, Griesheim,
near Frankfurt.
[C.A.C.] Clayton Aniline Co., Manchester.
[C.I.B.] Societe pour I'industrie chimique or Society of
Chemical Industry (Ges. f. chem. Ind.), (formerly
Bindschedler & Busch), Basle. f
Glaus & Co., Clayton, Manchester.
Colne Vale Chemical Works, Milnes bridge, Hudders-
field.
[D.] Dahl & Co., Barmen.
[D.H.] L. Durand, Huguenin & Co., Basle and Huningen.
[G.] J. R. Geigy & Co., Basle.
[H.] Read Holliday & Sons, Ltd., Huddersfield.
Carl Jtiger, Diisseldorf-Derendorf .
* This firm has been taken over by Messrs. Glaus & Co.
t This company has purchased the Easier chen^ische Fabrik,
and recently the Clayton Aniline Co., Manchester.
xiv LIST OF PRINCIPAL FIRMS
[K.] Kallc & Co., Biebrich a/Rhein.
Kinzlberger & Co., Prague.
[L.] Farbwerke MilJilheim (formerly A. Leonfiardt & Co.,
Mtihlheini, near Frankfurt a/M.).
Leipziger Anilinfabrik (Beyer & Kegel, Lindenau-
Leipzig).
Leitch & Co., Milnes bridge, Huddersfield.
[Lev.] Levinstein, Ltd., Blackley, Manchester.
[M.L.B.] Farbwerke vormals Meister, Lucius und Bruning,
Hoehst a/Main. (Hochst Farbwerke.)
H. N. Morris, Ardwick, Manchester.
Niederldnd isch e Far ben- und Ch emilcalienfabrik,
Delft,
[0.] K. Oetder, Anilin- und Anilinfarben-Fabrik, Offen-
bach a/Main.*
Pick, Lanye & Co., Amsterdam.
[P.] Societe anonyme des matieres color antes et produits
cJiimiques de Saint-Denis (Poirrier and I)alsace),
Paris.
ScJidllkopJ Aniline & Chemical Co., Buffalo, U.S.A.
[S.] Sandoz & Co. (formerly Kern & Sandoz), Basle.
[S.U.R.] Societe chimique des U sines du Rhf>ne (formerly
Gilliard, Monnet & Cartier), Lyoii.
[T.M.] Fabriques de produits cJiimiques de Thann et
Mulhouse, Mulhouse (Alsace).
[W.] Weiler-Ter Meer, Chemische Fabrik, Uerdingen
a/Rhein.
Wiescher & Co., Haeren.
Williams Bros., London.
* Now the property of the Chemische Fabriken Griesheirn-
Elektron.
THE MANUFACTURE OF ORGANIC
DYESTUFFS.
INTRODUCTION.
THE colour industry commenced with the discovery of
JUauvelne in 1856 by William Henry Perkiii, then assis-
tant to Hofmann at the Royal College of Chemistry in
London. Two years later this dyestuff was manu-
factured by Perkin senior and junior in their works at
Greenford Green, and met with considerable success
under the trade names of Tyrian purple, Perkin 9 s violet,
Mauve or Mauveine. The year 1859 is not less memor-
able, being the date when Verguin, chemist at the dye-
works of Messrs. Renard Brothers and Franc in Lyons,
discovered Aniline red. The process became the pro-
perty of the c; Fuchsine " Company with a capital of
four million francs. Discoveries followed with astonish-
ing rapidity, Magenta (Fuchsine) itself being converted by
chemists into Imperial violet, Lyons blue, Paris violet, etc.
The wonderful development of this new industry,
almost exclusively in French hands, gave splendid
promise ; but the complex mechanism of the reactions
giving rise to these new products was not at all under-
stood. The percentage composition and exact arrange-
ment of the molecular structures of these dyestuff s were
unknown, and the French scientists did not foresee, or
pretended not to see, what the industry, as well as pure
science, could gain by such determinations. Even if at
O.D.
2 ORGANIC DYESTUFFS
the beginning, chance and empiricism have played the
greater part in the first stages of a discovery, this state
of things was destined to become rapidly modified.
Owing to the impetus caused by the adoption of the
theories of valency and of radicles, and hence of
structural formulae, by which the characteristic pro-
perties of carbon compounds were diagrammatically
represented by simple symbols, organic chemistry passed
through a period of rapid development, of which 110
parallel can be found in the history of other sciences.
(See A. Haller, Report of the Paris Exhibition, 1900.)
Unfortunately these theories met with great opposition
in France. This was all the more difficult to overcome
as it was supported by eminent scientists who united
in refusing to recognise such novel theories. Whereas
Gerhardt, Wiirtz and others, in France, continued their
efforts in a hopeless struggle, which finally ended in
a triumph for these theories, in Germany the appli-
cation of these views by Kekule, Hofmann, V. Meyer,
Graebe and Liebermann, Baeyer, and others, was
so productive that these theories were accepted with
enthusiasm, and found favourable conditions for their
successful application.
These advances of organic chemistry immediately had
their effect on the German colour industry, causing
its rapid development. It borrowed its methods, views,
symbols and language from science. The chemist
engaged in the industry thus found a firm scientific
basis, an aid and reliable guide with whiph he did
not hesitate to launch out resolutely in the way which
led him to his great discoveries.
Thus, this industry, after having "undergone a period
of expansion in France as well as in England,
gradually crossed the frontier and established itself
in Germany and Switzerland, where it has developed
so rapidly that to-day their supremacy cannot be
disputed.
Nothing will illustrate the economic importance of
INTRODUCTION
this industry better than the following statement relat-
ing to the prosperity of the main German firms :
FIRM.
Number
of
Chemists.
Number
of
Employees.
DIVIDENDS PAID PER CENT.
1897
1900
i
1908
1909
1910
1911
1900
1900
Badische Anilin- und
Sodafabrik, Lud-
wigshafen -
148
8,640
24
24
22
24
24
25
Farbwerke vormals
Meister, Lucius,
<fc Sr fining, Hochst
a/Main
120
3,555
26
26
27
27
27
30
Farbcnfabriken
Bayer, Elberfeld -
145
7,889
18
18
24
24
29
Aktiengesellschaft fur
Anilinfabrikation,
Berlin
55
1,800
m
15
18
18
20
Leopold Gassella,
Frankfurt -
60
1,800
Kalle & Co., Bieb-
rich a/Rhein
-
4
10
10
10
In 1908, of the various smaller- colour firms : Weiler-Ter Meer,
paid 7 per cent. ; Grtinau, Landshoff und Meyer, 10 per cent. ;
Chemische Fabrik Oriesheim Elektron, 14 per cent.
On the 1st of January, 1905, an association of the
Badische Anilin- und Sodafabrik, Farbenfabriken Bayer,
and Berlin Aktiengesellschaft was formed for a period
of fifty years. This combine owns the Augusta-Victoria
coal-mine, and has large interests in the new Norwegian
works for the electro-synthetic manufacture of nitric
acid. The firms Kalle, Leopold Cassella, and Meister,
Lucius und Bruning have also formed a similar combine.
In this small volume the author proposes to illustrate
the numerous and varied reactions by which the chemi-
cal industry has succeeded in converting comparatively
simple substances extracted from coal-tar, such as
benzene, naphthalene, anthracene, phenol, etc., into
4 ORGANIC DYESTUFFS
innumerable dyestuffs, the formulae of which are gener-
ally very complex.
Having briefly indicated the processes by which the
principal constituents can be isolated from tar, some of
the principal methods of converting the raw materials
into other compounds, which are conveniently called
intermediate products, will be examined. It would be
difficult to bring all the methods at the disposal of
the chemist for attaining his object into such a limited
space, and it has therefore been necessary to make
a selection. The author has been guided in his choice
by the aim of presenting facts to the reader in as con-
nected a chain as possible, and in such a manner that,
starting with simple reactions, the complex reactions
involved in the production of colouring matters are
reached in progressive stages.
Having outlined the methods of preparation and con-
stitutional formulae of the hydrocarbons and phenols,
there will be considered in order :
1. Sulphonation, which gives mono-, di-, tri- or poly-
sulphonic acids of benzene, naphthalene, phenol, etc.
2. Alkaline fusion, which constitutes a general method
for the synthesis of the phenols, starting with the
sulphonic acids, of which the preparation has just been
given. Fusion with alkalies of mono-, di- or poly-
sulphonic acids yields new phenols or naphthols, poly-
phenols or hydroxynaphthols, and by more careful
treatment hydroxy-sulphonic acids.
3. Nitration, which yields nitro-compounds with the
original hydrocarbons, whereas nitration of sulphonic
acids or hydroxy-sulphonic acids gives a number of new
intermediate products : nitro- and hydroxy-nitro-com-
pounds, and nitro- and hydroxy-nitro-sulphonic acids.
4. Reduction converts all these nitro-compounds into
amines, which are more or less complex according to
the original nitro-compound.
5. On alkylation, amines or phenols yield secondary or
tertiary amines, or phenolic esters.
INTRODUCTION 5
Hence, commencing with some four or five substances
of simple composition, an enormous number of inter-
mediate products is obtained by suitable application
of these reactions. It will be understood that here
again it will be necessary to limit the number of sub-
stances mentioned. Being limited to the general rules
which apply to these various processes, several typical
examples have been chosen to illustrate the manu-
facture of the more important intermediate products
which should be considered in connection with the study
of dyestuffs.
The study of the dyestuffs themselves forms the
third part of this book. As it is necessary to distin-
guish between substances which are merely coloured
and those which possess tinctorial properties, it has
appeared advisable to outline Witt's chromophore
theory, and also the different methods of dyeing by
which dyestuffs are fixed on textile fibres. In order to
simplify the study of the chemistry of colouring matters,
they have been divided into fifteen groups which will
be examined in order.
This book has not been written with the object of
stating the various theories which have been put forward
with regard to the constitution of organic dyestuffs,
but is intended for the thoughtful reader who wishes
to understand the various treatments to which the raw
materials are subjected, and the manner in which they
are carried out in practice in the manufacture of colouring
matters. As the study of these changes is so intimately
connected with organic chemistry, of which it constitutes
one of the most attractive chapters, it has appeared not
only interesting, but absolutely essential to show by
what particular series of reactions, analytical and
synthetical, chemists have succeeded in determining
the structure of the principal colouring matters, such
as Magenta, Alizarin, Indamine, Indigo, etc.
To facilitate further reading, it has been considered
advisable to give some of the original references. The
6 ORGANIC DYESTUFFS
restricted character of this volume does not allow a
complete bibliography to be given, and only recent
references have been mentioned, as it is always easy
to obtain the earlier references from more detailed
treatises.
A. WAHL.
NANCY,
l&h May, 1911.
FIRST PART.
RAW MATERIALS.
CHAPTER I.
COAL TAR.
IN the manufacture of organic dyestuffs, a considerable
number of products obtained from coal tar are used
as raw materials, and it is for this reason that these
dyestuffs are sometimes given the name " Coal-tar
Colours/ 5
The tar is obtained by the dry distillation of coal,
which yields three kinds of products : gases, liquids
(ammoniacal liquor and tar), and a solid residue of coke.
This process is carried out in different apparatus, accord-
ing to whether the distillation is carried out with a view
to manufacturing illuminating gas, or coke for metallur-
gical purposes. In gas-works, the carbonisation is carried
out in retorts. Closed brick chambers, arranged in
parallel in series of 12, 18 or 24, are used as coke-
ovens. In gas-works, retorts are at present being
replaced by chambers similar to coke-ovens. The coke-
ovens arc usually erected in the immediate neighbourhood
of the mine.
In the original apparatus the gases and condensable
products which escaped from these ovens were not
8 ORGANIC DYESTUFFS
collected, but were sent into pipes placed in the
walls of the chambers, where their combustion gave
the heat necessary to maintain the distillation. In
1866, a French engineer, Knab, erected coke-ovens at
Commentry in which the condensable products could be
recovered, only the gases being burnt. Since that time
these processes have been perfected, and the use of coke-
ovens suitable for the recovery of the bye-products is
now general. Although they were only adopted in
Germany in 1881, the amount of tar which they have
produced has increased rapidly. The yield of tar from
coke-ovens in Germany alone was :
In 1897, 52 thousand tons.
1898, 78
1900, 93
1902, 190
1904, 273
In 1908, 800 thousand tons of tar, worth about a
million sterling, were produced : 585 thousand tons from
coke-ovens, 204 thousand tons from gas-works, 3,050 tons
from water-gas works, and 8,000 tons from oil-gas
works.
The yield of tar depends on the nature of the coal,
the temperature, and the time of carbonisation ; average
gas-coal yields 4-7 to 6-7 per cent., and coal for coke-
manufacture only 1-3 to 4-0 per cent, of tar, as it is not
so rich in volatile constituents.
Composition of Tar. Coal-tar is a thick black liquid of
density varying from 1-1 to 1-3. It is a mixture of a
large number of substances, containing aromatic hydro-
carbons from the simplest, such as benzene, to the
more complex, such as rctene, picene, chrysene, etc.
It contains nitrogen, oxygen and sulphur compounds,
such as the pyricline bases, phenols, etc., and also
particles of carbon which give it the black colour.
Treatment of Tar. The separation of these various
COAL TAR 9
products is effected by a series of operations, partly
physical, partly chemical, of which a full description
cannot be given in this book, but will be found in
Leroide's book on the gaseous fuels and their bye-
products (published by Doin et fils, Paris ).* Only a
resume of the process will be given.
After the tar has been freed from ammoniacal liquor,
it is fractionally distilled from direct fired iron boilers,
the products being separated into either four or five
fractions, according to the works. In this separation,
the temperature and sometimes also the density of the
distillate are used as a guide. The various fractions
collected have the following names :
I. Fraction 105-110, Crude Naphtha.
II. 110-210, L^<^-
III. 210-240, Carbolic oil
IV. 240-270, Heavy or Creosote oil
V. ,, Above 270, Anthracene oil.
or only four fractions may be collected :
I. Up to 150, Light oil (density less than 1).
II. From 150 to 210, Medium oil (density greater
than 1).
III. From 210 to 280, Heavy oil.
IV. Above 300, Anthracene oil.
The residue remaining after distillation is a thick
mass called pitch. The naphtha is separated from the
water by decantation ; the liquid is first shaken with
dilute sulphuric acid to remove basic substances, and
then with concentrated sulphuric acid to resinify the
unsaturated hydrocarbons and sulphur compounds
(thiophen). Finally, after washing twice with caustic
soda and with water, the product is again fractionally
* See also G. Lunge, Coal Tar and Ammonia.
10 ORGANIC DYESTUFFS
distilled, giving benzols and solvent naphtha. On
redistilling these give more or less pure hydrocarbons :
benzene, toluene, xylenes, etc., which have still to be
further purified.
The fight oils are distilled and separated into two
portions : the fraction up to 170 is added to the naphtha
and treated as described later, the other fraction
ia added to the carbolic oil. The latter contains
phenols and naphthalene, which are separated by
shaking with caustic soda, when the phenols dissolve,
whereas the naphthalene and other hydrocarbons are
insoluble. On acidifying the alkaline solution, crude
carbolic acid separates and is fractionally distilled,
giving phenol and cresols. The insoluble hydrocarbons
are distilled to give naphthalene. The heavy oils are
used for lubricating, impregnating wood, etc. ; they are
also used in the manufacture of illuminating gas, being
decomposed by heat; the gaseous products formed
arc collected. On leaving to crystallise, anthracene
011 gives crude anthracene, and on redistilling the
oil gives a further yield of anthracene. (For details
see Rispler, Chem.-Ztg., 1910, 34, 261, 279, 286, 349,
407).
According to Lunge, the distillation of one ton of
coal-tar yields on an average :
Ammoniacal liquor - - 30 gallons.
Naphtha - - - - 6-3
Light oils - - - - 13 4 to 15-0 gallons.
Heavy oils - - - G8 gallons.
Pitch - 0-54 ton.
The relative amounts of the various fractions obtained
naturally vary with the nature of the coal, the tempera-
ture of carbonisation and the apparatus in which it is
effected. If the temperature is low, the yield of tar is
greater, and it is then richer in light hydrocarbons
(benzene, toluene, etc.). If the temperature is higher,
COAL TAR
11
12 ORGANIC DYESTUFFS
the volatile products are submitted to the decomposing
effect of the heated parts of the carbonising apparatus,
and the amount of light hydrocarbons .diminishes, whilst
that of the more condensed products (naphthalene,
anthracene, etc.) is increased. This occurs in coke-
ovens.
The treatment of the tar is outlined in the diagram
on the previous page.
CHAPTER II.
HYDROCARBONS.
Benzene, C 6 H 6 , is a colourless liquid, of high refractive
power, possessing a characteristic smell. It boils at
80-5 and solidifies at 4 C. Its empirical formula cal-
culated from the percentage composition is CH, but
vapour density determinations show that it has the
molecular formula C 6 H 6 .
It has been shown that all the six hydrogen
atoms are equivalent (Franchimont, Nolting), and should
therefore be symmetrically arranged. A number of
structural formulae have been suggested which would
account for the chemical properties of benzene, the
one generally adopted being that of Kekule. In this,
benzene is represented by a regular hexagon, each corner
being occupied by a CH group ; the carbon atom being
tetravalent, these atoms are linked alternately by single
and double bonds :
CH
HC / ^ CH
HC
or
CH
CII
The bonds and the carbon and hydrogen atoms are
often omitted, and benzene represented by a hexagon.
Amongst the experimental proofs supporting this formula
may be mentioned the well-known synthesis of benzene
carried out by Berthelot by heating acetylene to a dull
14 ORGANIC DYESTUFFS
red heat, when it polymerises, giving, amongst other
hydrocarbons, benzene :
3C 2 H 2 = C 6 H 6 .
The acetylene having been obtained by direct com-
bination of hydrogen and carbon in the electric arc,
Berthelot's synthesis is a complete synthesis from the
elements.
Toluene, C 7 H 8 , is a colourless liquid, of B.P. 111, and
only solidifies at a much lower temperature than in
the case of benzene. Its density at 15 is 0-872. Its
properties are analogous to those of benzene. It has
the formula C 7 H 8 , and its constitution is established
by the fact that careful oxidation gives benzoic acid,
C 6 H 5 .COOH, the calcium salt of which decomposes on
heating with soda-lime to give benzene. Toluene is
therefore methyl benzene, its formula being C 6 H 5 . CH 3 :
or
Xylene, C 8 H 10 , is present in the light oils in the frac-
tions boiling at about 140. The xylene so obtained
is not one substance, but a mixture of the three isomers
possible according to theory ;
CH 3
or^o-xylene. weto-xylene. para-xylene.
HYDROCARBONS 15
These substances cannot be separated by distillation,
as their boiling points do not differ sufficiently ; the para-
compound is easily isolated by treating the mixture with
concentrated sulphuric acid, when the ortho- and meta-
xylenes are attacked, whilst the ^ara-xylene remains
unchanged. All the three compounds are liquids, the
crude xylene extracted from tar being a mixture of the
three isomers in the following proportions :
or^o-xylene (B.P. 142-143) 10-25 per cent,
meta-xylene (B.P. 137-138) 60
pam-xylene (B.P. 136-137) 10-25
Cumene, C 9 H 12 , extracted from tar, is also a mixture, in
which the most important isomer is
Commercial products :
The properties of the hydrocarbons which have
just been outlined are those of the pure substances.
Commercial samples, called benzols, generally consist of
a mixture of several hydrocarbons and have different
ifames according to the proportions in the mixture.
In addition to commercially pure benzene, there are
90's (known as " nineties benzol "), 30's, 10's, and O's
benzols, that is, 90, 30, 10 or per cent, of the product
distils below 100 C. (with the thermometer in the
liquid). Such samples of benzene contain toluene
and xylenes which can be separated by careful dis-
tillation. There are other impurities which it is
impossible to remove by distillation, such as carbon
disulphide and sulphur compounds (thiophen). It is
then necessary to resort to chemical processes, which are
16
ORGANIC DYESTUFFS
very numerous. Carbon disulphide can be eliminated
by saturating the benzene with moist ammonia, which
requires about 0-25 per cent, of the gas (Schwalbe,
Zeitschr. f. Farben- und Textil.-Ind., 1904, 3, 462). Haller
and Michel (Bull Soc. chim., 1896, 15, 390) have out-
lined a process for removing sulphur compounds which
consists of treating the benzene with aluminium chloride,
this being the subject of a patent of the Societe des
matieres* colorantes de Saint-Denis (D.R.P., 79,505).
Agitation of the hydrocarbon with sulphuric acid also
removes thiophen, but at the same time a small
quantity of the hydrocarbon is sulphonated and becomes
soluble in water. This may be avoided by first passing
in a current of nitrous fumes to resinify the thiophen,
which is then removed by rapid shaking with con-
centrated sulphuric acid (Mon. sci., 1905, 499).
The following table gives the composition of some
commercial products :
Benzene.
Toluene.
Xylenes.
Cumenes.
Naphtha-
lene.
90's Benzol -
84
13
3
50's Benzol -
43
46
11
O's Benzol -
15
75
10
Solvent naphtha I.
5
70
25
,, n.
35
60
5
Heavy naphtha
5
80
15 *
Test for thiophen in benzene. Several drops of con-
centrated sulphuric acid are taken in a test-tube, a small
crystal of isatin added, and a small amount of the
benzene added. If thiophen is present, an intense blue
colour will bo obtained on shaking the sulphuric acid.
Naphthalene, C 10 H 8 , is the hydrocarbon present to
the largest extent in coal-tar ; whereas 100 kgm. of tar
only give on an average 2 kgm. of benzene, | kgm. of
HYDROCARBONS 17
toluene, and | kgm. of phenol, some 5 to 6 kgm. of
naphthalene are obtained. It is a white solid substance,
with a characteristic odour. It melts at 80, and boils
at 218. Naphthalene sublimes very readily, and this
property is used in its purification. The constitution
of naphthalene is represented by two condensed benzene
nuclei ;
CH CH
HC S^/\ CH
HC
CH CH
The formula is established by the fact that on oxida-
tion naphthalene yields the dibasic acid, phthalic acid,
which has the following constitution :
COOH
COOH
On oxidising nitronaphthalene, a mixture of phthalic
and nitrophthalic acids is obtained : the naphthalene
molecule is therefore symmetrical, and formed by the
fusion of two benzene rings.
Anthracene, C 14 H 10 , was discovered in coal-tar by
Dumas and Laurent in 1832. It is a white crystalline
solid, of M.P. 216-5 and B.P. 351. The anthracene
deposited from the anthracene oil is very impure, and
does not contain more than 30 to 32 per cent, of anthra-
cene. It is purified by treating with solvents in which
it is only slightly soluble, such, as pyridine (D.B.P.
42,053, April 15th, 1887), liquid sulphur dioxide (Bayer
Co., D.R.P. 68,484 ; F.P. 220,621), acetone (Bayer Co.,
D.R.P. 78,861), and other substances (D.R.P. 111,359,
113,291, 122,852, 164,508, 178,764 (1906)). Finally
O.J>, B
18
ORGANIC DYESTUFFS
it is sublimed (Rispler, Ohem. Ztg., 1910, 34, 261 ct seq.).
Anthracene has the constitution :
no CH CH
no
HO
CTI
CIL
HO CH CH
If solutions of anthracene are exposed to the action
of light, a less soluble polymeride of anthracene, para-
anthracene, of M.P. 244, is deposited. Anthracene is
found in tar together with methylanthracenes, of which
there are two isomerides, a and J3.
Phenanthrene, C U H 10 , is an isomeride of anthracene
having the formula :
CII
CH CH
It has M.P. 99, and B.r. 340.
CHAPTER III.
THE PHENOLS.
Phenol or Carbolic acid, C 6 H 5 OH. Pure phenol forms
colourless prismatic needles of characteristic odour.
It has M.P. 42 and B.P. 182. In contact with air
it slowly becomes pink. Phenol dissolves in alkalies,
from which solution it is reprecipitated by acids ; it
forms true salts with alkalies in which an atom of
hydrogen in the phenol is replaced by an atom of a
monovalent metal. Phenol corresponds to the formula
C 6 H f) OH ? its salts or phenates to C 6 H 5 (OX), as will be
detailed later (see p. 35) ; phenol is easily synthesised
from benzene by way of benzene sulphonic acid, and
from this it is obvious that phenol contains the benzene
nucleus. It is hydroxy benzene :
on
Phenol gives a violet coloration with ferric chloride.
Cresols, CH 3 . C 6 H 4 OH. The cresols, which are present
together with phenol in crude carbolic acid, are hydroxy-
toluenes ; there are three isomers :
x'OII
OH
weto-cresol. para-cresol.
M.P. 30, B.P. 188-5. M.P. 4, B.P. 200. M.P. 36, B.P. 199.
20 ORGANIC DYESTUFFS
They are present in the following proportions :
ortJio - 35 per cent.
meta - - - - 40 ,,
para - - - - 25
The cresols are used as raw material in the manufacture
of certain dyes tuffs and as antiseptics. The mixed
cresols are on the market as a colourless liquid, boiling
at 185 to 285, under such names as " tricresol,"
" enterol," etc. The slight solubility of cresol in water
(2 per cent.) is a disadvantage for its use as an anti-
septic, although its bactericidal power is much greater
than that of the more soluble mixture of phenol and
soap (" sapocarbol").
SECOND PART.
INTERMEDIATE PRODUCTS.
WITH comparatively few exceptions the raw materials
described in the preceding chapter cannot be directly
converted into dyestuffs. It is first of all necessary to
convert them into intermediate products which differ
in properties from the raw materials due to the intro-
duction of new groups. These intermediate substances
are obtained by a number of very simple general reactions,
of which the main ones can be referred to five types
which will be described in the following order :
1. Sulphonation.
2. Alkaline fusion.
3. Nitration.
4. Reduction of nitro-compounds.
5. Alkylation.
Only the general principles relating to these different
operations will be indicated, with an outline of the
manner in which they are used in practice.
CHAPTER IV.
SULPHONATION.
SINCE 1834 it has been known that, on heating certain
aromatic hydrocarbons with concentrated sulphuric
acid, they become soluble in water and alkalies. This
reaction has since been made of a general character, and
may be applied to a very large number of organic
substances, which are converted in this way into sul-
phonic acids. The readiness with which substances
sulphonate varies considerably. Some, such as benzene
and toluene, are converted into sulphonic acids even by
ordinary cold acid ; others require the use of mono-
hydrated (100 per cent. H 2 S0 4 ), or fuming acid contain-
ing more or less sulphuric anhydride. It is sometimes
even necessary to work at a high temperature with
an acid which contains a large amount of anhydride.
Under these conditions it is often difficult to limit the
action to the formation of monobasic acids, and there
result disulphonic, trisulphonic or polysulphonic acids.
Constitution of the sulphonic acids. The mechanism
of sulphonation is very simple. In the case of benzene
the reaction is :
C 6 H 6 + H 2 S0 4 = C 6 H 6 S0 3 + H 2 0.
The benzene sulphonic acid thus obtained gives well-
defined salts with bases ; the sodium salt has the com-
position C 6 H 5 SO 3 Na, one atom of hydrogen in the
original acid being replaced by an atom of sodium. As
there is only one hydrogen atom which possesses this
property, the formula C 6 H 6 SO 3 is written as C 6 H 5 .S0 3 H.
SULPHONAT1ON 23
The complex SO 3 H has been given the name " sul-
phonic acid group," and sulphonation may be regarded
as an operation by which an atom of hydrogen in an
organic compound is replaced by the sulphonic acid group.
If this substitution is repeated two, three, or more
times, di-, tri- or polysulphonic acids are obtained.
According to the relative positions which these groups
take up in the molecule, a greater or less number of
isomers can exist. Amongst the factors which exert the
greatest influence on the orientation of the sulphonic
group or groups may be mentioned the temperature,
concentration of the sulphuric acid, the duration of the
reaction, and the presence of substituted groups before
sulphonation. The addition of small quantities of
mineral inorganic substances, such as mercury salts
and boric acid, exerts a peculiar catalytic influence on the
rate of sulphonation, causing a different orientation of
the sulphonic acid group (Iljinsky, Ber., 1903, 36, 4194 ;
Schmidt, Ber., 1904, 37, 66 ; Liebermann and Pleus,
ibid, 646 ; Farbenfabriken Bayer, D.R.P. 149,801 ;
Iljinsky, E.P. 25,738 (1903) ).
The sulphonic acids are also obtained by the action
of chlorsulphonic acid on organic compounds, thus :
R-H +C1S0 8 H -R . S0 3 H + HCJ,
where R is an organic radicle. This method is not of
frequent application.
Practical Details of Sulphonation.
If sulphonation is to be carried out with fuming
sulphuric acid of a certain concentration, it is first
necessary to prepare the acid by mixing ordinary
sulphuric acid with the necessary amount of fuming
acid, which is at present sold in commerce with 75-90
per cent. SO 3 content. Formulae exist from which it
is easy to calculate the proportions of the mixture. For
example, if a is the percentage of anhydride to be con-
tained in the required acid, b the strength of the fuming
24 ORGANIC DYESTUFFS
acid available, and c the concentration of the ordinary
acid, then the amount x of this acid which it will be
necessary to add to 100 parts pf fuming acid is given by
the formula: ^ 22(b-a)
* = 100+0-22(a-c)'
Recently Prats (Ghent. Ztg., 1910, 34, 264) has given
a modified formula ; thus, to prepare an amount a of
fuming acid, containing h per cent, of SO 3 , from an
amount # of a fuming acid containing k per cent. SO 3
and an amount y of an ordinary acid containing s per
cent. H 2 S0 4 : 9ft +40(100-*)
X ~ a 9k+ 40(100-5)'
y^a -x.
The substance to be sulphonated is often dissolved in
the ordinary sulphuric acid and the calculated amount
of fuming acid added.
Apparatus. The sulphonation is carried out in cast-
iron vessels ; in case ordinary sulphuric acid is used
without addition of fuming acid, it is preferable to have
a lead-lined apparatus. The cover is provided with a
certain number of holes (Fig. 1).
A is for introducing the fuming acid and the sub-
stance to be sulphonated.
B is for the axis of the stirrer.
C is a cast-iron pipe passing to the bottom of the
vessel to which a pipe F can be joined for emptying
the vessel.
D is the thermometer.
After having introduced the necessary amount of
sulphuric acid of the desired concentration, the substance
to be sulphonated is added in small portions through the
opening A. The readings of the thermometer enable
the progress of the operation to be followed, and, accord-
ing to whether the process is to be effected at a low or
high temperature, cold water or steam is circulated
through the outer jacket which surrounds the vessel.
SULPHONATION
25
For higher temperatures the vessel is placed in an
oil-bath.
The progress of the sulphonation is followed by
taking a small sample from time to time, and examining
its solubility in water or in alkalies, according to the
substance being prepared. When the reaction is
finished, the opening A is closed by a clamp plate, the
stirrer is stopped, the tube F connected to C, and com-
pressed air passed into the apparatus.
FIG. 1. Apparatus for Sulphonation Process.
For this purpose the axis of the stirrer is generally
made hollow, and it is only necessary to connect it
with the compressed air supply. The sulphonated pro-
duct flows out by pipe F, and is collected in a large lead-
lined wooden vat containing cold water or ice. The
sulphonic acid may be insoluble or soluble in water. In
tho first case, the precipitated sulphonic acid is removed
by using a filter-press, after having diluted sufficiently
26
ORGANIC DYESTUFFS
with water. In the second case, two methods are avail-
able for isolating the sulphonic acid from its solution.
Sometimes the addition of common salt causes the
precipitation of the sodium salt of the sulphonic acid,
which is then readily filtered off. If this method is not
successful, the sulphuric acid is neutralised by slaked
lime, the calcium sulphate formed being removed by
using a filter-press, when the calcium salt of the sulphonic
acid passes through into the filtrate. This solution is
then treated with sodium carbonate, giving a solution
of the sodium salt of the sulphonic acid, which is often
used as such for further operations.
Details of the plant used for the manufacture of
sulphonic acids are given in Fig. 2.
Flu. 2. Manufacture of Sulphonic acids.
A is the vessel in which the sulphonation is effected.
When the process is finished, the product is conveyed
into the vat J3, which is lined with lead and contains
sufficient water to finally dilute the solution to 5 per cent,
acid content. If the acid is soluble, common salt or lime
SULPHONATION 27
is added to J5, and then the contents of the vat are run
into an underground reservoir M, which is a compressor.
This apparatus is provided with a number of fittings
in its upper portion as indicated in the figure. C com-
municates with the vat B. D is used to connect the
compression apparatus with the atmosphere, E is a
pipe passing to the bottom for leading the product into
the filter press F, O is the entrance for compressed
air.
When the content of the vat B has been discharged
into the vessel M , the taps C and D are closed and
E and O opened. The liquid with the precipitate
which it retains in suspension is forced into the filter
press, which retains the precipitate and alloAvs the liquid
to pass.
Principal Sulphonic Acids of the Hydrocarbons.
Derivatives of Benzene.
Benzene monosulplionic acid, C 6 H 5 . S0 3 H, is obtained
by boiling equal volumes of benzene and concentrated
sulphuric acid for twenty-four hours, under a reflux
condenser ; or by heating one part of benzene and five
parts of concentrated sulphuric acid for two days in
an autoclave at 100. The product is poured into
water, saturated with lime, and the filtrate from the
calcium sulphate concentrated.
Benzene disulplionic acid, C 6 H 4 (S0 3 H) 2 . If benzene
or its monosulplionic acid is treated with an excess of
fuming sulphuric acid, a mixture of the two isomeric
disulphonic acids (meta and para) is formed :
S0 3 H
S0 3 H
28 ORGANIC DYESTUFFS
Larger quantities of the wefo-acid are formed at
lower temperatures and when the reaction is of short
duration. The following is an example of a commer-
cial preparation (Mon. sci., 1878, 1169). Fifty parts
of benzene are stirred with 200 parts of concentrated
sulphuric acid at a temperature of 40, rising gradually
to 100 ; when all the benzene has disappeared, the
liquid is heated for one or two hours at 275, allowed
to cool, and then poured into 1,000 parts of cold water
and neutralised by lime. The liquid which flows out of
the filter-press is decomposed by potassium carbonate
and the solution filtered from the calcium carbonate
and evaporated until its SP. GR. is 1-275. On cooling,
the potassium salt of the m-disulphonic acid crystallises
out, whilst that of the isomer remains in solution.
Derivatives of Toluene.
On treating toluene with concentrated sulphuric acid
or fuming acid which does not contain much anhydride,
a mixture of the three isomers (ortho, meta, and para)
is obtained. Of these acids, the ortho- and para- are
the most important ; the first is used in the prepara-
tion of saccharin, and the second gives p-cresol on
fusion with alkali. There are a number of processes
(D.R.P., 35,211, 57,391) available for isolating these
acids from their mixture.
Derivatives of Naphthalene.
On sulphonation naphthalene gives two isomeric mono-
sulphonic acids, termed naphthalene a- and /3-mono-
sulphonic acids, of the following constitutions :
S0 3 H
/\ /\
S0 3 H
a -acid. /?-acid.
SULPHONATION 29
In the case of the di- and tri-sulphonic acids, the
isomers become more numerous, and it is necessary to
have a definite nomenclature This is done by dis-
tinguishing the carbon atoms of the naphthalene nucleus
by numbers or Greek letters, commencing at the top
of the right-hand ring :
or
Naphthalene Monosulphonic Acids.*
When naphthalene is treated with concentrated
sulphuric acid, a mixture of the a- and /3-monosulphonic
acids is obtained in varying proportion according to
the temperature. Thus at 100 the mixture contains
80 per cent, of the a-acid and 20 per cent, of the /3-acid,
whilst at 170 it contains 75 per cent, of the /3-acid and
only 25 per cent, of the a-acid. This shows that the
a-acid is not stable at high temperatures, and to obtain it
the preparation must be carried out at a low temperature.
According to the recent researches of Euwes (Bee. trav.
ch. P.B., 1908, 18, 298) the pure a-acid is obtained by
treating naphthalene with the equivalent amount of
sulphuric acid at a temperature of 80. On heating
the naphthalene with double its weight of concentrated
sulphuric acid at a temperature lower than 80, only
the a-acid is produced in appreciable quantities ; by
using the same proportions of the reacting substances,
but heating for six to eight hours at 180, the /2-acid is
formed almost exclusively.
The acids may be separated by making use of the
different solubilities of their calcium, barium, lead,
*See G. Schuliz, Die Chemie des Steinkohlenteers, Braun-
schweig, 1900, vol. i., 186.
30 ORGANIC DYESTUFFS
etc., salts ; the salts of the /3-acid are less soluble than
those of the a-acid.
a- Monosulphonic Acid. This acid is prepared com-
mercially by heating 150 to 175 kilograms of concen-
trated sulphuric acid to about 40-50 in a cast-iron
vessel (Fig. 1), and then adding 100 kilograms of finely
powdered naphthalene in small portions. The sulphona-
tion commences immediately, and, when almost all the
naphthalene has disappeared, the liquid is poured into
water, neutralised with lime and filtered. The filtrate
is decomposed by sodium carbonate, filtered, and the
liquor concentrated until the sodium salts crystallise out,
when they are separated by fractional crystallisation.
/3- Monosulphonic Acid. 100 kilograms of naphtha-
lene are added to 100 kilograms of warm concentrated
sulphuric acid ; the mixture is heated at 160 for three
hours, then raised to 170, and finally heated for one
hour at 180. The product is then allowed to cool
and is poured into salt solution, when the sodium salt
of the naphthalene y6-sulphonic acid crystallises out,
whilst the small quantity of the a-isomer and of the
disulphonic acid remain in solution.
Naphthalene Disulphonic Acids.
The further sulphonation of the two naphthalene
monosulphonic acids yields different mixtures of the
isomeric disulphonic acids according to the experi-
mental conditions. The second sulpJionic acid group
never enters the ring to which the first group is attached.
Hence naphthalene a-sulphonic acid gives a mixture of
the 1 : 5- and 1 : 6-disulphonic acids, and the /3-acid
a mixture of the 2 : 6- and 2 : 7-acids. These two acids
are very important and may be obtained direct from
naphthalene. Thus, on heating one part of naphthalene
with five parts of sulphuric acid for four hours at 160
no monosulphonic acid is obtained, but there is produced
a mixture of the 2 : 6- and 2 : 7-disulphonic acids :
SULPHONATION 31
,S0 3 H
and
The first of these acids is often called naphthalene
/3-disulphonic acid, the second being known under the
incorrect name of naphthalene a-disulphonic acid. If
the sulphonation is carried out at a higher temperature
for twenty-four hours, the 2 : 7 -acid disappears and the
2 : 6-acid is the main product ; the same result can be
obtained by sulphonating naphthalene /i-monosulphonic
acid. To separate the two disulphonic acids, they are
converted into their calcium salts ; that of the 2 : 7 -acid
is the most soluble. Use may also be made of the fact
that the calcium salt of the 2 : 6-acid is insoluble in a
saturated salt solution, whereas the calcium salt of the
2 : 7 -acid dissolves in this solution on heating. (Ebert
and Mertz, Ber., 1876, 9, 609; Baum, D.R.P. 61,730;
Griinau, Landshoff and Meyer, D.R.P. 48,053.)
Naphthalene Trisulphonic Acids,
Of these acids, one of the most important is the
1:3:6 acid :
SO 3 H
JSO S H
This acid was discovered by Gurcker and Rudolph
(D.R.P. 38,281), who obtained it by the following
method : one part of naphthalene is added to eight
parts of fuming sulphuric acid containing 24 per cent, of
anhydride, and the mixture heated for several hours
at 180. Another method is to add one part of naphtha-
lene to six parts of fuming sulphuric acid containing
40 per cent, of anhydride, taking care to keep the
32 ORGANIC DYESTUFFS
temperature below 80 C., the heating being continued
on a water-bath until all the anhydride has disappeared,
when the liquid is poured into water, neutralised with
lime, and treated as usual.
Sulphonic Acids of the Phenols,
Phenol sulphonic acids. Kekule (Ber., 1869, 2, 330)
showed that sulphuric acid acts on phenol even in the
cold, giving a mixture of the oriho- and para-sulphonic
acids ; the latter acid is formed as the principal pro-
duct when the reaction is carried out at higher tempera-
tures. The separation of these acids is a matter of
considerable difficulty; according to Obermiller (Ber.,
1908, 41, 696), the most convenient method is the
fractional crystallisation of their barium or magnesium
salts.
CHAPTER V.
ALKALINE FUSION.
IN 1867, Wurtz and Dusart in France and Kekule in
Germany discovered simultaneously that, on fusing
benzene monosulphonic acid with caustic potash, potas-
sium pheriate and sulphite are produced :
C 6 H 5 S0 3 K + 2KOH - C 6 H 5 OK + K 2 SO 3 4- H 2 O.
This reaction may be applied to the greater number of
the sulphonic acids, which are converted in this manner
into phenols. Alkaline fusion is hence a process by which
the sulphonic acid group SO 3 H may be replaced by the
hydroxyl group OH.
Other methods are available for the synthetic pre-
paration of the hydroxy-hydrocarbons : for example,
the ainido-derivatives may be converted into diazo-
compounds and these decomposed by water, or the
amido -compounds may be heated under pressure with
water. The conversion of an amiiie into phenol or
iiaphthol can be effected by treatment with an excess
of a solution of sodium bisulphite (sr. OR. 1-32 to 1-38),
and subsequently saponifying with aqueous alkali :
R . NH 2 +NaHS0 3 =ROSO a Na + NH 3
ROSO 2 Na +2NaOH =R . ONa +Na 2 SO 3 +H 2 O.
Alkaline fusion of the di-, tri- or poly-sulphonic
acids under certain conditions causes the successive
replacement of one, two or more sulphonic groups by
hydroxyl groups, giving hydroxy-sulphonic acids or
polyphenols. Hence this constitutes a yery general and
O.D. c
34 ORGANIC DYESTUFFS
important synthetic process. It has recently been
extended by Sachs (JBer., 1906, 39, 3006; *D,R.P.
173,522 (1904), B.F. 359,064 (1905), D.R.P. 181,333
(1905) ), who, noting the analogy between the formulae
of caustic soda and sodamide : Na(OH), Na(NH 2 ), has
fused the sulphonic acids with sodamides. In this
manner the sulphonic group is replaced by the amido-
group :
C 6 H 5 S0 3 Na + NaNH 2 - Na 2 S0 3 + C 6 H 6 NH 2 .
Alkaline fusion may also be applied to halogenated
derivatives.
Practical Details of the Alkaline Fusion Process.
The alkali generally used is caustic soda, the action
of which is not always the same as that of caustic
potash. The solid alkali is heated in an iron vessel
fitted with a stirrer with a small amount of water until
the mass is completely liquid, and to this is added the
sulphonated derivative. The temperature and length
of the reaction vary with the nature of the product.
The fusion requires a high temperature which sometimes
greatly alters the organic substance. In such cases
it is convenient to replace the fused alkali by a more or
less concentrated solution, carrying out the operation
in a closed vessel capable of standing the pressure
(an autoclave) ; the more dilute the alkaline solution
the higher the temperature at which the process may be
carried out. Substances may also be added to lower
the melting point, for example, a mixture of alkalies
(caustic soda and potash, alkalies and alkali alcohol-
ates) may be used. It is to be noted that in the case
of the complex polysulphonic acids, the concentration
of the alkali exerts an important influence on the nature
of the compound formed, as the sulphonic group
eliminated by concentrated or fused alkali is not always
the same as that which is eliminated by dilute caustic
alkali. (D.R.P. 68,721).
ALKALINE FUSION 35
Whichever method is used, when the reaction is
finished, the product is poured into water, acidified with
a mineral acid, boiled to free from sulphur dioxide, and
allowed to cool. If the phenol is insoluble, it is easily
separated ; in case it is soluble, it is separated by steam
distillation, or shaking with a suitable solvent, or, when
dealing with a phenol sulphonic acid, it is isolated as in
the case of a sulphonic acid.
Phenols Derived from Benzene.
Synthesis of Phenol. 100 parts of sodium benzene
sulphonate are fused with 75 parts of caustic soda, the
temperature being raised to 300, and then gradually to
330, this temperature being maintained until the mass
has become liquid. The melt is poured into water,
acidified, and the phenol separated. The yield is about
80-90 per cent, of the weight of sulphonate used. (G.
Schultz, Die Chemie des Steinkohlenteers, 1900, vol. i., 139.)
Dihydroxybenzenes, C 6 H 4 (OH) 2 .
OH OH
OH
Pyrocatechol. Resorcinol. Quiiiol (hydroquinone).
All three isomers are important ; they are obtained by
very different methods. The only one of interest at
present is the one for which alkaline fusion is used,
meto-dihydroxybenzene or resorcinol.
Preparation of Resorcinol. Sixty kilograms of sodium
benzene disulphonate are heated at 270 with 150 kilo-
grams of caustic soda in an iron vessel fitted with a
stirrer. The resulting mass is dissolved in 500 litres
of water, acidified with sulphuric acid, filtered, and
the sodium sulphate allowed to crystallise out. The
36 ORGANIC DYESTUFFS
resorcinol is extracted by repeatedly shaking with ether
in closed vessels ; after distilling oil the ether, the white
residue is purified by distillation or sublimation. Resor-
cinol forms rhombic crystals of M.P. 118, B. P. 276-5.
Hydroxy-Derivatives of Naphthalene.
By alkaline fusion the naphthalene monosulphonic
acids are converted into phenolic compounds called
" naphthols." The naphthols are related to naphthalene
in the same way that the phenols are to benzene. Just as
there are two naphthalene monosulphonic acids, so two
naphthols are known, a and /? :
OH
/\ x\
lOII
a-naphthol. /3-naphthol.
Preparation of the Naphthols.
ft-Naphthol. Two parts of caustic soda, to which has
been added a small amount of water, are fused in an
iron vessel provided with a stirrer, and one part of
dry, powdered sodium naphthalene /^-sulphonate added,
the temperature being gradually raised to 300. When
the reaction has finished, the product is dissolved in
water and decomposed with acid ; the precipitated
/?-naphthol is dried and purified by distillation in vacuo.
In this preparation the fused caustic soda may be
replaced by a concentrated solution, the heating being
carried out in an autoclave at 270 -290.
a-Naphthol may be prepared by fusing naphthalene
a-sulphonic acid with caustic soda, but it is preferable to
use the method which involves the substitution of
OH for the amido-group in a-naphthylamine. This
replacement can be carried out in a very simple manner
ALKALINE FUSION 37
by heating the sulphate or hydrochloride of a-naphthyl-
amine in an autoclave with water at 200 for three or
four hours, when a-naphthol and the corresponding
ammonium salt are produced. (Meister, Lucius &
Bruning, D.E.P. 74,879.)
NH 2 HC1
+ H 2 - I I 4- NH 4 C1
Another method is to convert a-naphthylamine into
the diazo-compound (see p. 98), and from this into
a-naphthol by boiling.
Properties of the Naphthols. a-Naphthol is a solid
crystalline substance, colourless when pure, but becomes
brown on exposure to air. It is insoluble in water,
very soluble in alcohol, ether, and other organic solvents ;
it melts at 96 and boils at 278-280. ,8-Naphthol is
similar to the a-compound, but has a slightly different
smell ; it melts at a higher temperature, 122, and may
hence be distinguished from a-naphthol, which melts
in boiling water ; it boils at 285-286. Like the
phenols, the naphthols are weak acids, being soluble
in caustic alkalies, but not in alkaline carbonates.
Naphthol Sulphonic Acids.
The naphthol monosulphonic acids can be obtained
in different ways :
1. By alkaline fusion of the disulphonic acids ;
2. By sulphonation of the naphthols.
The naphthol di-, tri- or poly- sulphonic acids can
be similarly prepared by alkaline fusion of the naphtha-
lene polysulphonic acids, but it is better to sulphonate
the naphthols, as alkaline fusion of the polysulphonic
acids often yields dihydroxy-naphthalene sulphonic
acids.
38 ORGANIC DYESTUFFS
1. Formation by Alkaline Fusion.
N ( aphthalene 2 : 7-disulphonic acid can be converted
jnto /?-naphthol monosulphonic acid and then into
2 : 7-dihydroxyiiaphthalene.
] SO 3 H s 3 n { T i JI OH i
2 : 7-Naphthol sulphonic acid or tc F acid " is prepared
as follows (D.R.P. 42,112 and 45,221) : 100 kilograms
of sodium naphthalene disulphonate are made into a
paste with 400 kilograms of a 50 per cent, solution of
caustic soda, and heated at 200-250 until an acidified
sample gives traces of 2 : 7-dihydroxynaphthalene on
extraction with ether. The mixture is then poured into
1,000 litres of water, acidified with hydrochloric acid,
freed from sulphurous acid by boiling, and allowed to
cool, when the sodium salt of F acid crystallises out.
2 : 1-Dihydroxy naphthalene. One part of sodium
naphthalene-2 : 7-disulphonate is fused with two and a
half parts of caustic soda at a temperature of 290-300
in an atmosphere of hydrogen. On acidifying and
extracting with ether, evaporation of the ethereal solu-
tion gives crystals of the dihydroxynaphthalene (Ebert
and Mertz, Ber., 1870, 9, 609).
l-Naphthol-3 : Q-disulphonic acid is obtained by heating
the naphthalene trisulphonic acid with caustic soda at
170-180 (D.R.P. 38,281).
2. Sulphonation of the Naphthols.
Derivatives of a-naphthol. (Friedlander and Taussig,
Ber., 1897, 30, 1456). rx-Naphthol sulphonates readily ;
on heating with concentrated sulphuric acid at 50-60 C.
it yields a mixture of the 1 : 2- and 1 : 4-monosulphonic
acids and a small amount of disulphonic acid. By
carrying out the operation at 40 with a slight excess of
ALKALINE FUSION 39
concentrated sulphuric acid, the sulphonation may be
limited to the production of a mixture of the mono-
sulphonic acids :
OH OH
r so 3 n
SO 3 H
1 : 2-acid. 1 : 4-acid.
The 1 : 4-acid is the most important and is called
Nevile and Winther's or N.W. acid. To separate it from
the 1 : 2-isomer, the property of diazo-compounds to
react with the two acids at different velocities is used,
the 1 : 2-acid reacting first. When the reaction is
completed the azo-dyestuff formed is precipitated by
salt and separated, when the filtrate is a solution of
N.W. acid, which is generally employed directly. The
yield is 80 to 85 per cent, of the theoretical.
Nevile and Winther's acid may also be obtained by
diazotising 1 : 4-iiaphthylamine sulphonic acid, usually
termed naphthionic acid (see later, p. 62), and then
boiling with water (Nevile and Winthor, Ber., 1880, 13,
1940 ; D.R.P. 26,012) ; or heating naphthionic acid with
caustic soda (D.R.P. 46,307), thus :
Nil* ONa
-f NaOH = NH 3 +
SO 3 Na SO 3 Na
Finally, on heating 1 :4-chlornaphthalene sulphonic acid
with caustic soda, N.W. acid is obtained (D.R.P. 77,446).
Naphthol di- and tri-sulphonic acids. Of these acids,
the most important are those which may be obtained
directly by sulphonation of a-naphthol ; these are
l-naphthol-2 : 4-disulphonic acid and l-naphthol-2 : 4 : 7-
40 ORGANIC DYESTUFFS
trisulphonic acid (D.R.P. 10,785 and 77,996), which are
used for the preparation of nitro-dyestuffs.
OH
) 3 H S0 3 11
and
so 3 ii
Derivatives of fi-napJithol. The sulphonated deriva-
tives of /?-naphthol are more important than those of
a-naphthol.
On treating /2-naphthol with concentrated sulphuric
acid at the ordinary temperature, there is first formed an
unstable 2-naphthol- 1-sulphonic acid, which, on con-
tinuing the reaction in presence of an excess of sul-
phuric acid, is converted into a mixture of the two
acids, 2-naphthol-8-sul])honic acid, or crocein acid, and
2-naphthol-6-sulphonic acid, or {ScMller acid.
SOoH SO oil
O O
lOH
2-Naphthol- Crocein acid (2 . g)> Schiiffer acid (2 : 6).
1-sulphomc acid. v '
The relative proportions of 2 : 8 and 2 : 6 acids ob-
tained depends on the temperature, amount of acid,
and length of the reaction. On sulphonating /3-naphthol
with twice its weight of sulphuric acid at a temperature
of 40-60, there is formed almost as much 2 : 8-acid
as 2 : 6-acid. Crocein acid (2 : 8) is obtained in larger
quantity by carrying out the sulphonation in the cold,
and allowing to stand for several days ; on the other
hand, Schaffer acid is formed in larger amount at 100.
The disulphonic acids are produced on sulphonating
with a larger amount of sulphuric acid at a temperature
ALKALINE FUSION
41
of 1 10 ; with fuming sulphuric acid the trisulphonic
acid is formed.
Crocein or Bayer acid, when prepared, contains some
of its isoincr, from which it can be separated in several
ways. One part of finely powdered /3-naphthol is added
to two parts of warm sulphuric acid (168 Tw.), and the
mass heated, the temperature being kept between 50
and 60. When the naphthol has disappeared, the liquid
is poured into water, neutralised with lime, and the mono-
sodium salts, C 10 H 6 (OH)S0 3 Na, isolated as usual. To
separate these, they are converted into neutral salts,
which are then treated with alcohol. The salt of crocein
acid dissolves, whereas that of Schaffer acid is insoluble.
There are other methods available for this separation
(D.R.P. 20,231, 30,077, and 33,857. See also G. Schultz,
Ber., 1884, 17, 461 ; Glaus and Voltz, Ber., 1885, 18,
3155 ; Schaffer, Journ. f. prakt. Chem., 1869, 106, 449).
Disulplionic acids. By further sulphonation the 2 : 8
and 2 : 6 monosulphonic acids are converted into di-
sulphonic acids. Thus, crocein acid gives 2-naphthol-
6 : 8-disulphonic acid, generally called " G acid " :
S0 3 H
S0 3 H
,OH
lOH
S0 3 T1'
On sulphonation Schaffer acid gives a mixture of the
2:6: 8-acid and an isomer 2:3:6, called " R acid " :
SO 3 H
G acid.
S0 3 BJ
OH
S0 3 H
R acid.
42 ORGANIC DYESTUFFS
From this it will be easily understood that on energetic
sulphonation /J-naphthol will give rise to a mixture of
these two acids. They are separated by using differ-
ence in the solubility of their sodium salts in alcohol
or in a saturated salt solution. The sodium salt of
G acid dissolves in alcohol, whilst that of R acid is
insoluble (D.R.P. 3,229) ; also the salt of G acid is
more soluble in a saturated salt solution than the salt
of R acid (D.R.P. 33,916 (1886) ). Finally, they may
be separated by combining with a diazo-compound, this
taking place more slowly with G acid, which may hence
be isolated (D.R.P. 26,491).
The 2-naphthol-3 : 7-disulphonic acid 1 obtained by
sulphonation of 2-naphthol-7-sulphonic acid (D.R.P.
44,079 ; and Weinberg, Ber., 1887, 20, 2906 ; sec p. 38),
is called 5-acicl.
Trisulphonic acids. Sulphonation of R and G acids
yields the same acid, 2-naphthol-3 : 6 : 8-trisulphonic
acid.
SO 3 H SO 3 H
This acid is more easily obtained by sulphonating
/3-naphthol with fuming acid at about 140-150 (D.R.P.
22,038).
CHAPTER VI.
NITRATION.
COLD concentrated nitric acid reacts with most aro-
matic compounds, converting them into nitro -deriva-
tives. This reaction is generally accompanied by the
development of a considerable amount of heat, and it
is necessary to keep this within certain limits so that
the reaction is not too vigorous. Under these con-
ditions, the nitration yields a nitro-derivative and
water. Thus, in the case of benzene, the reaction may
be expressed by the equation :
C 6 H 6 + HNO 3 - C 6 H 5 N0 2 + H 2 O.
Thus, nitration may be considered as a process by which
a hydrogen atom from the ring of an aromatic compound
is replaced by the nitro-group (NO 2 ).
Nitration may be effected by using the theoretical
amount of acid, but the water formed in this reaction
exerts a retarding action owing to the resulting dilu-
tion of the acid. Sometimes this dilution is reduced
by using a large excess of nitric acid, but in this
case it becomes difficult to limit the nitration to the
formation of a mono-nitro -derivative, and di~, tri- or
poly-nitro-derivatives may be produced by the substitu-
tion of nitro-groups for 2, 3, or more, hydrogen atoms.
The most convenient method for avoiding the diluting
effect of the water is to remove it as fast as it is formed.
This is easily done by carrying out the nitration in
presence of concentrated sulphuric acid ; for this, a
mixture of sulphuric acid with the required quantity of
44 ORGANIC DYESTUFFS
concentrated nitric acid, known as " mixed acid/' is
used.
In certain cases when it is essential to use nitric acid
free from water, the mixed acid is prepared by dissolving
dry powdered potassium nitrate in sulphuric acid, the
acid potassium sulphate formed remaining in solution.
Recently a mixture of fuming nitric acid and acetic
anhydride has been used for the nitration. This mixture
has somewhat peculiar properties, and the products
which it yields are often different from those given by
mixed acid or fuming nitric acid (Orton, J.C.S., 1002,
81, 806; Marquis, Bull. Soc. chim., 1903, 29, 276;
Bouveault and Wahl, ibid., 1904, 31, 847 ; Witt., Ber.,
1906, 39, 3901). Possibly this mixture contains the
mixed anhydride of acetic and nitric acids recently
isolated by Pictct and Khotinsky (Ber., 1907, 40, 1163)!
Practical Details of the Nitration. The compound to
be nitrated is placed in a cylindrical cast-iron vessel,
fitted with a stirrer, and closed by a cover which has
an opening for the gradual introduction of the mixed
acid. Another opening is fitted with an iron tube,
in which is placed the thermometer. The vessel is
put into another larger one, in which water can be
circulated to regulate the rise in temperature. A tap
is provided at the bottom of the apparatus for drawing
off the contents. When the reaction is complete, the
product is run into water ; nitro-compounds are
generally insoluble in water, some being liquids, others
crystalline. After standing for a. sufficient length of
time, the nitre-derivative is separated by dccantation
if it is liquid, or by filtration if solid, is shaken several
times with water to free from acid, and then purified
by distillation or crystallisation.
With regard to the acid solution from which the
nitro-derivative has been separated, it only contains a
small amount of nitric acid, as only the theoretical
quantity of acid is used, and moreover the reaction
is generally quantitative. On the other hand, the
NITRATION 45
solution contains all the sulphuric acid, and this is
recovered by concentrating in lead-lined vessels ; this
treatment destroys any organic substances present, and
eliminates the nitric acid.
Nitro-Derivatives of the Hydrocarbons.
Derivatives of Benzene.
Nitrobenzene, C 6 H 5 N0 2 , was discovered by Mitscher-
lich in 1834, by treating synthetic benzene with nitric
acid ; in 1847, Mansfield prepared the same product by
nitrating benzene obtained from coal-tar. At present
nitrobenzene is a very important commercial product,
the apparatus used permitting the nitration of several
hundreds of kilograms at the same time. The mixed
acid necessary for the nitration of 100 kilograms of
benzene, made by mixing 115 kilograms of nitric acid
(90 Tw.) and 180 kilograms of sulphuric acid, is poured
slowly into the benzene. At the commencement of
the reaction, the liquid is cooled by a current of water
passing through the apparatus, but towards the end the
temperature is allowed to rise to 90-100. If the process
is carried out carefully, the yield is almost theoretical :
100 parts of benzene give 150 parts of nitrobenzene, the
theoretical yield being 157. According to the D.E.P.
221,787 (1907) of the Fabriqucs de Saccharine, late
Fahlberg, List and Co., of Salbke-a./Elbe, a theoretical
yield of nitrobenzene is obtained by adding concen-
trated sulphuric acid to a mixture of benzene and an
alkaline nitrate at a suitable temperature.
Properties. Nitrobenzene is generally a light yellow
liquid, but when pure is a colourless, highly refractive
liquid of B.P. 206-207, which on cooling crystallises in
long needles of M.P. 7 ; its density at 15 C. is 1-208.
Nitrobenzene is slightly soluble in water, and is miscible
in all proportions with organic solvents. It is volatile
in steam, six parts of water being necessary for the
46 ORGANIC DYESTUFFS
separation of one part of nitrobenzene in this manner.
Pure nitrobenzene or a mixture with nitrotoluenes is
obtained, according to whether the benzene used for the
nitration was pure or contained toluene. Nitrobenzene
is used mainly for the manufacture of aniline ; it is also
used in perfumery under the name of " oil of mirbane."
Dinitrobenzene is obtained when nitrobenzene or
benzene itself is nitrated with hot mixed acid in the
apparatus used for the preparation of nitrobenzene.
Under these conditions a mixture of the three dinitro-
benzenes is formed, but the main product is meta-
dinitrobenzene,
N0 2
the oriho- and para-isomers only being formed in small
quantities.
m-Dinitrobenzene crystallises in slightly yellow
needles, of M.P. 89-8, and B.P. 297. It is somewhat
soluble in boiling water. The or^Ao-isomer has M.P. 118,
the para-compound, M.P, 171. m-Dinitrobenzene is
used for the preparation of w-nitraniline, m-phenylene-
diamine, and in the manufacture of explosives.
Derivatives of Toluene.
The nitration of toluene yields a mixture of the three
isomeric mtro-toluenes which consists mainly of the
oriho- and para- varieties ; wea-nitrotoluene is only
formed in small amounts. The relative proportions
in which the oriho- and para-compounds are obtained
varies with the conditions of the nitration, the con-
centration of the acid, and the temperature. Whereas
with concentrated nitric acid about 66 per cent, of para-
nitrotoluene is obtained, with the mixed acid from 60 to
66 per cent, of the or^o-derivative is formed (Girard and
NITRATION 47
de Laire, Nolting and Forol). According to Friswell
(J. Soc. C/iem. Ind. y 1908, 258), who has studied the in-
fluence of varying conditions, the proportion is to be
considered fixed in practice as 35 to 40 per cent, of the
^para-derivative and 60 to 65 per cent, of the ortho-
derivative. When the nitration is carried out with nitric
acid and acetic anhydride, the proportion of o-nitro-
toluene formed is considerably increased, 88 per cent,
of the ortho- and 12 per cent, of the ^ara-compound
being obtained (Pictet and Khotinsky, Ber., 1907, 40,
1163) ; finally, by the action of nitrous fumes on toluene
vapour at 300-400, 11 per cent, of the meta- and 89 per
cent, of the or^o-nitrotoluene is obtained (Chem. Fabrik
Grunau, Landshoff and Meyer, D.R.P. 207,170).
Toluene is nitrated as in the case of benzene,
and in similar apparatus. The product is transferred
to vessels cooled with ice, when the ^para-nitro toluene
crystallises out. The crystals are separated, and the
oil remaining is fractionally distilled in vacuo. This
oil is a mixture of ortho- and ^ara-nitro toluene, and the
difference in the boiling points of these two substances
218 for the ortho-, 238 for the jpara-variety is not
sufficient in itself to obtain a complete separation.
The first and last fractions contain practically pure
ortho- and para-nitrotoluene respectively, but a large
middle fraction is obtained which contains considerable
amounts of the joara-derivative. Hence, this is cooled,
giving further crystals of jpara-nitrotoluene and an oil
which is added to the distillation from the next operation.
Other processes exist for the separation (D.R.P. 78,002
and 92,991), but they are not practicable commercially.
o-Nitrotoluene, obtained as above, is an amber-coloured
liquid of B.P. 218-219 which solidifies on cooling and
melts at 10*5. The pure o-nitrotoluene of commerce
contains as impurities some m-, and a small amount
of ^-nitrotoluene. On cooling to -5 to -10, it
crystallises partially, and the pure crystals of o-nitro-
toluene formed melt at - 4 ; this process has been used
48 ORGANIC DYESTUFFS
for its purification (Hochst Farbwerke, DM. P. 158,219,
Nov. 1903 ; B.F. 350,020 ; F., viii., 88).
p-Nitrotoluenc crystallises in yellow prisms of M.P. 54
and B.P. 238. It is insoluble in water.
The two nitrotoluenes may be separated from the
diluted nitration mixture by steam distillation, 3 parts
of the o/^Ao -compound or 2 parts of the para-compound
passing over with 100 parts of water.
Dinitrotoluene. On nitrating toluene with hot mixed
acid, 1:2: 4-dinitrotoluene is obtained. The same
product results from the nitration of either the o- or
p-nitrotoluene :
CHo CHo CH
1:2: 4-dinitrotoluene is a crystalline substance of
M.P. 71. It is used for the preparation of w-toluylene-
diamine, and in the manufacture of certain explosives.
Naphthalene Derivatives.
Naphthalene can yield two mono-nitro-derivatives :
a- and /3-nitronaphthalene ; only the first one is formed
by the nitration of naphthalene, the /3-isomer being pre-
pared by indirect methods.
a-Nitronaphthalene was discovered by Laurent in
1835. Its commercial preparation was described by
O. Witt (Cfiemische Industrie, 1887, 10, 216). A mixture
of 200 kilograms of nitric acid (76 Tw.), 200 kilograms
of concentrated sulphuric acid, and 600 kilograms of
the acid remaining from the previous operation, is placed
in a cast-iron vessel, which can be cooled, and which is
fitted with a stirrer provided with arms. 250 kilograms
of powdered naphthalene are added through an opening
in the cover, the addition taking one day for its com-
NITRATION 49
pletion in such a manner that, by cooling with water
flowing through the outer chamber, the temperature
of the mass is kept between 45 and 50. When the
process is finished, the liquid is allowed to run out by
the lower tap into a lead- lined wooden vat ; on allowing
to cool, the nitronaphthalene solidifies and forms a solid
cake on the surface of the acid. The liquid underneath
is separated. The nitronaphthalene is purified by
boiling with water, which dissolves the excess of acid
and frees from naphthalene, and then cooling rapidly
by a stream of cold water, which precipitates the nitro-
compound as a granular solid. Pure mlro-naphthalene
may be obtained by dissolving these lumps in cumene or
solvent naphtha, filtering, drying over calcium chloride,
and cooling in a freezing mixture. In this way satis-
factory crystals may be obtained, and these are separated
by a hydraulic filter press (Wagner, Fischer, and L.
Gautier, Traitf de chimtc iiidustridle, vol. ii..23G. Masson,
1903). u-Nitronapkthalene is insoluble in water, but
soluble in benzene, carbon disulphide, ether, and warm
alcohol. It forms long needles of M.r. 01 and B.P. 304.
Dinitronaphtlialcnes. Ten diniiroiiaphthalenes should
exist according to theory. On nitrating a-nitro-naphtha-
lene under ordinary conditions, a mixture of 1:5- and
1 : 8-diiiitroiiaphthalene is obtained :
NO 2 NO 2
and
a-dinitromiphthalene. /3-cli nitronaphthalene.
These two products are important intermediate
products for the manufacture of certain dyes tuffs.
They are easily obtained by treating naphthalene with
cold nitric acid, then adding sulphuric acid to the
mixture, and heating the resulting mass to complete
O.D. D
50 ORGANIC DYESTUFFS
the nitration. The product is washed with water,
shaken with carbon disulphide to free from a-nitro-
naphthalono, and then with acetone to remove the 1 : 8-
dinitro-compoimd. This treatment is continued until
the M.F. has been raised to 210-212. 1 : 5-dinitro-
naphthalene forms yellow needles which melt at 217 ;
1 : 8-dinitronaphthalene crystallises in rhombic plates
of M.P. 170.
Derivatives of Phenol.
Phenol reacts with warm dilute nitric acid, giving a
mixture of ortho- and jpara-nitrophenol. The pro-
portion of the ^am-derivative is much greater at lower
temperatures.
Nitration of Phenol. One part of phenol is mixed
with sufficient water to give a liquid ; the liquid so
obtained is slowly added to a mixture of two parts
of commercial nitric acid with four parts of water,
keeping the temperature at about 35. After one
or two hours, the oil is separated, washed with water,
and the isomers separated by steam distillation, the
orttoderivative only passing over with steam, leaving
a residue of the para-confound. The yield of nitro-
phenol is 3G to 44 per cent, of the weight of the phenol.
o-Nitvophenol crystallises in long yellow needles of
M.P. 45 and B.P. 214. Its salts are highly coloured.
p-Nitrophenol forms almost colourless needles of M.P.
114. Its salts are yellow. The nitration of both
these isomers yields the same dimtrophenol, whose
constitution must therefore be represented as that of
a 1 : 2 : 4-derivative :
OH
It is prepared by heating phenol with " mixed acid " at
130 to 140. It crystallises in plates of M.P. 114.
NITRATION 51
Nitrosulphonic Acids.
Nitrosulphonic acids may be obtained by two methods :
(1) sulphonation of the mtro-derivatives, or (2) nitration
of the sulphonic acids. These two methods may yield
identical products or isomers, and the method adopted
will depend on the compound to be prepared.
On treating nitrobenzene with fuming sulphuric acid,
it is converted into nitrobenzene m-sulphonic acid, whilst
on sulphonation p-nitrotoluene yields ^-nitrotoluene
m-sulphonic acid : NO
From these two examples it will be seen that in
benzene hydrocarbons the sulphonic acid and nitro-
groups tend to take up meta -positions to one another.
This is not the case in the naphthalene series. The
a- and /?- naphthalene monosulphonic acids yield on
nitration isomeric nitrosulphonic acids in which the
mtro-group occupies the a -position. The a-sulphonic
acid gives a mixture of the 1 : 8-, 1 : 5- and 1 : 4-nitro-
sulphonic acids, containing ()0 to 70 per cent, of the
1 : 8-acid, 20 per cent, of the 1 : 5-acid, the 1 : 4-acid
only being formed in small amounts.
NO., SO 3 H
(1:5)
52
ORGANIC DYESTUFFS
These acids are not generally separated, but are
converted by reduction into the naphthylamine sulphonic
acids, which are more readily isolated.
The nitration of the /3-sulphonic acid yields a mixture
of equal amounts of the 1 : 6- and 1 : 7-acids :
,S0 3 H
,so 3 ir
(1:7)
(1:6)
NO,
These acids were prepared by Cleve (D.E.P. 67,017 ;
Ber., 1886, 19, 2179), and are used in the preparation of
the corresponding a-naphthylamine sulphonic acids.
The di- and tri-sulphonic acids may be nitrated in a
similar manner, the most important derivatives being
the 1:3: 6-nitrodisulphonic acid and the 1:3:6:8-
nitro-trisulphonic acid :
SOoH NO.
SO 3 H
SO 3 H
S0 3 H
S0 3 H
which are produced by the nitration of the 2 : 7-di-
sulphonic and 1:3: 6-trisulphonic acids respectively.
CHAPTER VII.
REDUCTION OF NITEO-COMPOUNDS.
THE term " reduction " is applied to those reactions
which take place between any chemical compound and
hydrogen, which may be free or liberated in the nascent
state by the interaction of suitable substances or is
represented by other " reducing agents." In the case
of aromatic compounds, reduction may lead to the
addition of hydrogen to, or elimination of oxygen from,
the compound, or both reactions may occur at the same
time, as in the case of nitro-compounds.
The reduction of nitro-compounds leads to very
different products, according to the character of the
reducing agent employed and the conditions under
which the reaction is carried out ; thus there are acid,
neutral, and alkaline reducing agents.
The most common acid reducing agents are metals,
such as iron, zinc, or tin, in presence of a mineral or
organic acid, the hydrogen liberated reacting with nitro-
compounds as follows :,
R . N0 2 + 6H = R . NH 2 + 2H 2 0.
The product obtained in this way contains an NH 2
or awirfo-group in place of the nitro-group, the com-
pound formed being known as an amine. Under the
same conditions a dinitro-derivative would give a
diamine, and, generally, a polynitro-compomid would
give a polyamine. In case tin and hydrochloric acid
are used, the reduction is sometimes accompanied by
chlorination (von Braun, Ber. 9 1912, 45, 1274, 2910).
54 ORGANIC DYESTUFFS
Neutral reducing agents include substances, such
as zinc powder and aluminium amalgam, which decom-
pose water, yielding an insoluble oxide, thus :
Zn + H 2 = ZnO + H 2 .
In this case, reduction of the nitro- compounds yields
substituted hydroxylamines :
R . N0 2 + 4H = R . NHOH + H 2 0.
Certain neutral salts, such as the alkali sulphites,
convert nitro-compounds into amines, introducing at
the same time an S0 3 H group.
Alkaline reducing agents do not all act in the same
way. Thus zinc powder and caustic soda convert
nitro-derivatives into azoxy- (I.) or hydrazo- (II.) com-
pounds.
(I.) 2R . N0 2 -f 6H = R-N-N-R + 3H 2 0.
O
(II.) 2R.N0 2 + 10H = R-NH-NH-R + 4H 2 0.
Other alkaline reducing agents, such as ferrous oxide
(ferrous sulphate and ammonia), exert a more energetic
action, yielding amines. Finally, the alkali sulphides
and hydrosulphides exert a selective reducing action on
polynitro-compounds, and enable the reduction to be
limited to only one of the nitro-groups.
Catalytic reduction processes have been discovered
by Sabatier and Senderens, in which the vapour of
the substance to be reduced, mixed with hydrogen,
is passed over finely divided metals. (Senderens,
d'Andoque and de Chefdebiea, D.R.P. 139,407.)
Electrolytic Reduction. The electrolysis of water
yields hydrogen at the negative plate, and this can serve
as the reducing agent. The conditions under which the
electrolysis is to be carried out, viz. the medium, the tem-
perature, the nature of the cathode, and the presence of
certain salts, exert a great influence on the character of
the products obtained. (Elbs, Zeitsch. f. Electrochemie,
REDUCTION 5
5, 108; D.R.P. 100,233, 100,234, 100,610, 121,835,
121,899, 121,900, 150,800, etc.) For details, the special-
ised treatises on electrochemistry must be consulted.
The amines may also be obtained from hydroxy-
derivatives by heating in an autoclave with ammonia
and a condensing agent. The condensation is more or
less difficult to effect according to the hydroxy-derivative
in question. The condensing agents used are zinc
chloride, calcium chloride, and, recently, ammonium
sulphite. This last compound is particularly suitable
for converting a naphthol into naphthylamine, an
intermediate compound being formed, which, in presence
of ammonia, regenerates the ammonium sulphite and
yields the amine :
R . OH + (NH 4 ) 2 SO 3 = R-O-rSCVNI^ + NH 3 + H 2
RO-S0 2 -NH 4 + 2NH 3 = R . NH 2 + (NH 4 ) 2 S0 3 .
(Se6 also Buchcrer's method, Journ. f. prakt. Chem., (2)
1904, 69, 88 ; 70, 349 ; 71, 433 ; D.R.P. 117,471.)
In the case of naphthalene derivatives, these reactions
are carried out at about 100. In order to avoid loss
of ammonia, the process is conducted in an autoclave,
fitted with a stirrer, in case the original phenol or amine
is insoluble in dilute ammonia.
Amido-Derivatives of the Hydrocarbons.
Derivatives of Benzene.
Aniline or Phenylamine, C 6 H 5 . NH 2 . Aniline was
discovered by Unverdorben in 1826 in the products
of the dry distillation of Indigo. In 1835 Runge
isolated it from coal-tar, but it was not until 1842
that Zinin prepared aniline by reducing nitrobenzene
with ammonium sulphide. Bechamp first suggested
the commercial preparation of aniline by reduction of
nitrobenzene with iron turnings and acetic acid ; this
method is used at the present time, the acetic acid being
56 ORGANIC DYESTUFFS
replaced by the cheaper hydrochloric acid. In 1860
aniline was sold at over ten shillings a pound ; at present
a much purer article is sold at less than sixpence a
pound (G. F. Jaubert, Histoire de V Industrie suisse des
matihes colorantes).
The amount of hydrochloric acid used for the reduction
of the nitrobenzene by means of iron is much lower than
that which is necessary according to the following
equation :
C 6 H 6 N0 2 + 3Fe + 6HC1 - C 6 H 6 NH 2 -f 3FeCl 2 + 2H 2 0.
This is explained by the ferrous chloride formed acting
as a reducing agent, giving ferric chloride, which latter
is then reduced again to the ferrous condition by solution
of more iron :
2FeCl 3 + Fe = 3FeCl 2 .
Manufacture of Aniline. The vessels used are made
of boiler-plate, and are about six feet in height and
one to four and a half feet in diameter. (Fig. 3.)
An opening at the bottom allows of the vessel being
emptied. The cover contains several openings : A is
used for the axis of the stirrer, B for introducing the
iron turnings, being closed by a cast-iron plate or
wooden block, C is attached to a worm condenser. The
axis of the stirrer is hollow, so that steam may be intro-
duced by this means during the operation. ICO litres
of water, 100 kilograms of iron, and 30 to 40 kilograms
of hydrochloric acid are first placed in the apparatus,
and then 400 kilograms of nitrobenzene added with
constant stirring. To accelerate the reaction, steam
is passed in, and then 300 kilograms of iron added in
small amounts. The process lasts for eight hours, and
is so arranged that the vapours which escape are cooled
by a reflux condenser. When the process is finished
the acid is neutralised with lime, and the aniline pro-
duced separated by steam distillation. The vapours are
REDUCTION OF NITRO-COMPOUNDS 57
cooled in a worm condenser, when the liquid obtained
forms two layers which may be separated. One layer
is aniline, the other is water containing about 2 to 3 per
cent, of dissolved aniline. This water is used for pro-
ducing the steam necessary for the next operation, thus
recovering the aniline which it contains in solution.
Fig. 3.
The aniline is purified by distillation, the yield being
about 67 per cent, of the weight of nitrobenzene used
(theoretical, 76 per cent.).
Properties. Pure aniline is a colourless liquid of
B.P. 182, M.P. -8. It is heavier than water, having
SP. GR. 1-026 at 15 ; it is soluble in water to the extent
of 3 per cent. On exposure to air, aniline slowly becomes
brown. In commerce a distinction is made between
" aniline oil for blue," which is pure, and " aniline oil for
red," which is a mixture of aniline and the toluMines in
the following proportions : aniline, 10 to 20 per cent. ;
o-toluidino, 30 to 40 per cent. ; p-toluidine, 25 to 40 per
cent.
58 ORGANIC DYESTUFFS
Pure aniline or its hydrochlorido (" aniline salt ")
is used in dyeing for producing Aniline black. The
hydrochloride forms white crystals of M.P. 192, which
become greenish-black on exposure to air.
Phenylenediamines or Diamidobenzenes. Three isomers
exist, o-, m- and ^-phenylenediamines, the last two being
the most important.
m-Phenylenediamine is obtained by reducing m-
dinitrobenzene with iron and hydrochloric acid. It
forms crystals of M.P. 63, and boils without decom-
position at 277. When pure it is white, but becomes
brown in air.
p-Phenylenediamine may be obtained by the reduction
of jp-ni tramline, but is actually manufactured by the
reduction of amidoazobenzene (see p. 104). ' It forms
white crystals of M.P. 147, and B.P. 267.
Derivatives of Toluene.
Reduction of nitro-derivatives of toluene yields the
corresponding toluidines, or the bases formed by reducing
crude nitro toluene may be separated. For this purpose,
it has been proposed to effect the reduction with alkali
sulphides, which only attack the ^para-derivative and
leave the o-nitrotoluene unaffected (Losner, D.R.P.
78,002; Clayton Aniline Co., D.R.P. 92,991). The
mixture may also be reduced with iron and hydrochloric
acid, the ^-toluidine being partially separated by cooling.
In this case it is preferable to isolate the base in the
form of the hydrate which it forms on shaking the crude
product with somewhat less than its weight of crushed ,
ice ; the hydrate is then melted, and the p-toluidine
purified by distillation (Friswell, J. Soc. Chem. Ind.,
1908, 258). There are also separation processes which
depend on the difference in solubility of certain salts
of the toluidines, such as the phosphates, oxalates, etc.
(Lewy, D.R.P. 22,139), and on the action of nitrous
acid (Wiilfing, D.R.P. 37,932).
REDUCTION OF NITRO -COMPOUNDS 59
The most important toluidines are ortho- and para-
toluidine. o-Toluidine is a colourless liquid which boils
at 199 ; it becomes brown in air, and is slightly soluble
in water. ^p-Toluidine crystallises in colourless plates
of M.P. 45 and B.P. 198.
Toluylenediamines. The only important one is m-
toluylenediamine, which is obtained by the reduction
of 1 : 2 : 4-dinitrotoluene. It forms crystals of M.P. 99.
NH O
Derivatives of the Xylenes.
The xylidine obtained by the reduction of commercial
nitroxylene is a mixture of four isomers, the separation
of which is rather difficult and may be carried out in
several ways (D.R.P. 39,947, 71,969, 87,615. See also
Friedliinder, Monatsh. /. Chem., 1898, 29, 639).
Derivatives of Naphthalene.
Two mononitronaphthalenes are known, and yield on
reduction a- and /3-naphthylamine :
NH 2
As already mentioned (p. 48), a-nitronaphthalene is
easily obtained by nitration of the naphthalene, whereas
/3-nitronaphthalene can only be prepared with diffi-
culty by indirect means. Hence, the /3-nitro-compound
cannot be used for the manufacture of /3-naphthylamine,
60 ORGANIC DYESTUFFS
and it is better to commence with /3-naphthol, which is
easily prepared by the alkaline fusion of naphthalene
/?-sulphonic acid.
a-Naphthylaminc is manufactured by reducing a-nitro-
naphthalene with iron and hydrochloric acid, the rather
vigorous reaction being kept in hand by adding the
mtro-derivative in such a manner as to keep the tempera-
ture at about 50. When the reaction is finished, the
liquid is neutralised with lime, and the base separated
by passing in a current of superheated steam. It is
purified by distillation in vacuo, when it crystallises in
white plates, M.P. 50 and B.P. about 100. Commercial
a-naphthylamine generally contains a small amount of
the /3-isomer (Reverdin and Nolting, Sur la constitution
de la naplitaline, 1888, 35). The isomers may be
separated by treating with xylene (Weiler-Ter-Meer,
DJtf. 209,076).
(3-Naphthylamine is prepared commercially by heating
ten parts of /3-naphthol and 7-5 parts of a concentrated
solution of ammonia in an autoclave for one day at 200.
The excess of /3-naphthol is extracted by means of caustic
soda. The /3-naphthylamine is purified by distillation
in vacuo, when it crystallises to form plates of M.P. 112
and B.P. 294.
Sulphonated Derivatives of the Amines.
The amido-sulphonic acids may be obtained by several
general methods :
1. By the reduction of nitro-sulphonic acids ;
2. By the sulphonatioii of amines ;
3. By heating the naphthol sulphonic acids with
ammonia.
In certain cases it is possible to bring about the
reduction and sulphonatioii at the same time by treating
a nitro-derivative with a neutral sulphite (Piria, Ann.,
1851,78,34).
REDUCTION OF NITRO-COMPOUNDS 61
Derivatives of Aniline.
The two most important derivatives are the meta-
and ^ara-amidobenzene sulphonic acids, or metanilic
(I.) and sulphaniUc acids (II.) I
NH 9
SO 3 H
(i.) (ii.)
The first is prepared by reducing m-nitrobenzene
sulphonic acid. Sulphanilic acid is obtained by sul-
phonating aniline at 190, or, better, heating aniline
sulphate for several hours at 200-205, the latter being
the commercial method.
Derivatives of the Naphthylamines.
Derivatives of a-Naphthylamine.
All the seven isomeric a-naphthylamine monosulphonic
acids predicted by theory are known. The sulphonation
of a-naphthylamine has been studied by Erdmann
(Ann., 1893, 275, 193), who found that, on treatment
, with five parts of the ordinary sulphuric acid at 130,
it yields almost exclusively the 1 : 4 or naphthionic acid
if the reaction is only allowed to proceed for a short
time. If the action of the sulphuric acid is prolonged, the
1 : 4-acid disappears, and the 1 : 5- and the 1 : 6-isomers
are successively produced :
NH 2 NH 2
\J\J S 3 n '
SO 3 H SO 3 H
62 ORGANIC DYESTUFFS
Naphthionic acid (1:4) is produced by sulphonating
a-naphthylamine, but it is prepared commercially by
heating a-naphthylamine sulphate at 170-180 for eight
hours (Nevile and Winther, Ber., 1880, 13, 1940).
Better results are obtained if a certain amount of oxalic
acid is added to the sulphate. On sulphonating with
three and a half parts of fuming sulphuric acid containing
25 per cent. S0 3 , at 30 C., a mixture of the a-naphthyl-
amine 4 : 6- and 4 : 7-disulphonic acids is obtained, and
these are called " Dahl's acids " (D.E.P. 41,957).
80 3 n,
I I I
S0 3 H !
\s
SO 3 H SO 3 H
NapJithylamine 1 : 6- and 1 : 1-sulphonic acids are
prepared by the reduction of the corresponding iiitro-
sulphonic acids, using the mixture formed on nitrating
naphthalene /3-sulphonic acid (see p. 52), the mixture
obtained being known as " Cleve's acids " (Cleve, Ber.,
1887, 20, 74).
Trisulphonic acids. Of these, the most important is
the 1:3:6: 8-acid, formed by reduction of the corre-
sponding nitronaphthalene trisulphonic acid (Koch,
D.R.P. 56,058).
SO 3 H NH 2
Derivatives of (3-Naphthylamine.
On sulphonating /3-naphthylamine with three times its
weight of concentrated sulphuric acid at a temperature
of about 100, a mixture of four monosulphonic acids is
REDUCTION OF NITRO-COMPOUNDS 63
produced, the sulphonic acid group again attaching
itself to the ring which does not contain the NH 2 group.
The main products are the 2 : 8- and 2 : 5-acids, the
2 : 6- and 2 : 7-acids only being obtained in small
amounts ; the relative proportions vary with the
experimental conditions (Green, Ber., 1889, 22, 721 ;
Dahl, D.R.P. 29,084, 32,276).
Sulphonation by means of ordinary sulphuric acid
at 15-20 yields almost exclusively the 2 : 5-acid, whilst
on heating /?-naphthylamine sulphate to 200-210, the
2 : 6-acid is the main product. This acid, often called
" Bronner's acid," is prepared in a pure state by heating
Schaffer's /3-naphthol sulphonic acid under pressure
with ammonia (Liebmann, Mon. sci., 1885, 1043),
Under the same conditions, /3-naphthol sulphonic acid
(2 : 7), " F acid," yields /3-naphthylamine sulphonic acid
(Cassella, TXjR.P. 43,740).
S0 3 H' S
Bronner's acid (2:6). 2 : 7 -acid.
fl-Naphthylamine disulphonic acids. The most im-
portant are the /3-naphthyIaniine 3 : 6- and 6 : 8-di-
sulphonic acids, called respectively " Amido R acid "
and " Amido acid."
SO 3 H
S0 3 r
Amido R acid. Amido G acid.
These acids are obtained by heating the corresponding
/?-naphthol disulphonic acids with ammonia under
pressure.
(3-Naphthylamine 5 : 7 -disulphonic acid is obtained
64 ORGANIC DYESTUFFS
by the sulphonation. of 2 : 5-naphthylamine sulphonic
acid.
S0 3 H
Hydroxy-Derivatives of the Amines.
These compounds include the amido-phenols and
amido-naphthols, and may be obtained by the following
processes :
1. By reducing the nitro -derivatives of the phenols
or naphthols ;
2. Alkaline fusion of the amido -sulphonic acids ;
3. Heating a di- or a poly-phenol under pressure
with ammonia ;
4. Reduction of the azo-derivatives of phenols or
naphthols.
Benzene Derivatives.
AmidopJienols. Three isomers are known, meta, ortho
and para.
o-Amidophenol is prepared by reduction of the corre-
sponding nitro-phenol with ammonium sulphide. It
melts at 170.
m-Amidophenol may be obtained by alkaline fusion
of metanilic acid (D.R.P. 44,792), by reduction of ra-
nitrophenol, or by heating resorcinol with ammonium
chloride at 200 in an autoclave for twelve hours (D.R.P.
49,060). It melts at 120.
p-Amidophenol is obtained on the reduction of p-nitro-
phenol by means of zinc and hydrochloric acid. Another
method of preparation has been outlined by R. Vidal ;
nitrobenzene is reduced in sulphuric acid solution by
REDUCTION OI MTRO-COMPOUNPS 65
means of zinc dust, when the phenyl-hydroxylamine first
formed yields jj-amidophcnol in presence of aeid :
OH
NI10H
( )n reduction, p-azophenol yields >-amidophenol
(D.R.P. 82,426). This compound melts at 184.
Sulphonated Hydroxy-Derivatives of the Amines.
These compounds contain an amido-group, a hydroxy-
group and one or more sulphonic acid groups. They
are prepared :
1. By alkaline fusion of the di- or poly-sulphonic
acids of amines ;
2. By reduction of the azo-dcrivatives of naphthol
sulphonic acid.
The compounds derived from naphthalene are of
greatest interest.
AmidonajrfitJiol sufyhonic acids. Of these, the 2:8:6,
2:3:6 and 2:5:7 are the most important.
OH
/\ /\ /\
WH 2 SO^H,
JoH
OH
Amidonaphthol Amidonaphthol 9 . r . 7 -^ T
sulphonic acid G, sulphonic acid R.
or y-acid.
The first two compounds are prepared by fusing the
/3-naphthylamino disulphonic acids G and R with
caustic soda. The third is obtained by alkaline fusion of
O.D. E
66 ORGANIC DYESTUFFS
2-naphthylamine-5 : 7-disulphonic acid, and is called
" J acid."
Of the amidonaphthol disulphonic acids, the com-
monest is the 1 : 8 : 3 : 6, or cc H acid," which is prepared
by heating a-naphthylamine 3:6: 8-trisulphonic acid
with caustic soda at 180 (D.E.P. 69,722, 80,668). On
heating with caustic soda, H acid itself undergoes a
change, its amido-group being replaced by a hydroxyl-
group, giving 1:8:3: 6-dihydroxynaphthalene disul-
phonic acid, or chromotropic acid, which may also
OH NIL, OH OH
H acid. Chromotropic acid.
be obtained by heating a-naphthol or a-naphthylamine
trisulphonic acids (1 : 8 : 3 : 6) with caustic soda (D.B.P.
67,563, 68,721, 69,190, 75,153).
Nitro-Derivatives of the Amines.
The nitro-amines may be prepared by two methods :
1. Partial reduction of the dinitro-compounds ;
2. Nitration of the amines.
The second method is the one generally used, and to
avoid the nitric acid acting on the amido-group this
group has to be protected by acylating the amine.
The products resulting from the combination of an
amine with an organic acid by the elimination of a mole-
cule of water are termed acylated compounds. Thus,
aniline and acetic acid give acetanilide :
C 6 H 5 NH 2 + CH 3 COOH = H 2 +C 6 H 6 NH . COCH 3 .
Nitration is then effected as usual, and gives the nitro-
derivative of the acylated amine. This compound is
easily converted into the nitro-amine by heating with
dilute acids or alkalies to eliminate the acyl group.
REDUCTION OF NITRO-OOMPOUNDR 67
Derivatives of Aniline.
Three nitranilines exist, the most important being the
meta- and para-compounds.
o-Nitraniline is formed together with the para-
compound (see below). It melts at 71-5.
m-Nitraniline is prepared by partial reduction of the
dinitrobenzeiie by means of iron and acetic acid (A.
Wiilfing, D.R.P. 67,018), or ammonium sulphide (Mus-
pratt and Hofmann, Ann., 1846, 57, 215), or tin and
hydrochloric acid in alcoholic solution (Anschiitz and
Heusler, 13er., 1886, 19, 2161). m-Nitraniline has
M.P. 114 and B.P. 285.
p-Nitraniline, NO 2 . C 6 H 4 . NH 2 , is obtained by the
nitration of the acetyl derivative of aniline, acetanilide
(see p. 66), with mixed acid. Finely powdered acet-
anilide is dissolved in concentrated sulphuric acid in an
apparatus fitted with a stirrer, and the mixed acid gradu-
ally introduced, keeping the temperature at 40-50.
When the nitration has finished, the product is poured
into water to precipitate the nitro-acetanilide. This
is then separated and heated with caustic soda solution
to eliminate the acetyl group ; the p-nitraniline is
precipitated on cooling, whilst the o-iiitraniline formed
remains in solution. Under these conditions about
60 per cent, of the para- and 25 per cent, of the ortJio-
derivative is obtained (Nolting and Collin, Ber. y 1884,
17, 262).
jp-Nitraniline is also obtained by nitrating benzylidene-
aniliiie (Farbenfabriken Bayer, D.R.P. 72,173), or by
heating p-nitrochlorbenzene under pressure with am-
monia. (See also Muller, Chem. Ztg. 9 1912, 36, 1049 ;
Clayton Aniline Co., D.R.P. 148,749.) p-Nitraniline
crystallises in yellow needles of M.P. 147. Its principal
use is in the production of Paranitranilme red (" Para
red ") on cotton fibre (see p. 108).
CHAPTER VIII.
ALKYLATION.
i
BY this process, the acid hydrogen atom of a phenol
or an organic acid, or a hydrogen atom of the amido-
group in an amine, is replaced by an alkyl group. The
alkylation of phenols and acids is sometimes called
" estcrifieation," but it is preferable to reserve this
name for the alkylation of acids only.
Alkylation of Phenols.
In order to alkylate a phenol, it is converted into the
alkali salt, and then treated with certain substances,
such as the halogenated derivatives of the saturated
hydrocarbons, C n H 2n+1 X, where X is chlorine, bromine
or iodine ; methyl sulphate is also very convenient for
alkylation, as its boiling point (187) is high enough to
allow of its use in open apparatus at the atmospheric
pressure, whereas the alkylogens (halogen esters) havo
very low boiling points, and hermetically sealed appara-
tus (autoclaves) must be used, as the pressure attained
is frequently very high. The alkyl nitrates may also be
used for alkylation.
In the case of the simple alkyl esters, the reaction is
expressed by the general equation :
C 6 H 6 ONa +C n H 2n+1 X = NaX +C 6 H 5 . O . C n H 2u+1 ,
in which X may be chlorine, bromine, iodine, the nitrate
radicle, etc.
ALKYLATION b9
If methyl sulphate is employed, the reaction is as
follows :
C 6 H 5 ONa + S0 2 < = S0 a < + C 6 H 5 OCH 3 .
The phenol is converted into its sodium salt by
means of alkali alcoholates in alcoholic solution, a slight
excess of the alkylogen added, and the mixture heated
in a closed vessel. In case methyl sulphate is used, the
phenol is dissolved in a caustic alkali, the sulphate
added and the mixture stirred. Treatment with water
removes the mineral salts, and on shaking the product
with caustic soda to dissolve the phenol, the alkylated
derivative remains insoluble, and may then be purified
by distillation or recrystallisation.
Derivatives of Phenol.
Anisole, C 6 H 5 OCH 3 . It is a colourless liquid, boiling
at 152.
Phenetoh, C 6 H 5 OC 2 H 5 . Colourless liquid of B.P. 172.
Derivative of Dihydroxybenzene.
The most important is guaiacol, the monomethyl
ether of pyrocatechol.
OH
It is extracted from creosote, and crystallises in
large prisms of M.P. 32. It is used as a base for anti-
tuberculous medicines.
Alkylation of Amines.
In an amine, the two hydrogen atoms of the amido-
group may be successively replaced by alkyl radicles.
70 ORGANIC DYESTUFFS
Thus, aniline can give monoalkylanilines and dialkyl-
anilines :
C 6 H 5 NH 2 -> C 6 H 6 NHR -> C 6 H 5 N<^;
The name primary amine is given to amines which
contain the NH 2 group ; if only one hydrogen atom of
the NH 2 group has been replaced by an alkyl radicle, a
secondary amine is obtained ; and if both hydrogen
atoms are so replaced, the compound is termed a tertiary
amine. The same nomenclature is used if the character-
istic atoms of hydrogen in a primary amine are replaced
by other than alkyl radicles, only the methods of pre-
paration are different.
The alkylation of primary amines for the preparation
of secondary amines is almost always accompanied by
the formation of a tertiary amine. The separation of
the two bases cannot as a rule be effected by fractional
distillation, as the difference in their boiling points is
not sufficiently great. The salts of the secondary amines
are often solids, whereas those of the tertiary amines
are oils.
The alkylating agents used in commerce are methyl
and ethyl chlorides, produced at the moment when they
are required by heating the amine in an autoclave with
hydrochloric acid and the corresponding alcohol ; methyl
sulphate may also be used.
Secondary Amines.
Monomethyhmiline, C 6 H 5 .NH.CH 3 , is prepared com-
mercially by heating 55 parts of aniline hydrochloride
and 16 parts of methyl alcohol in an autoclave at 180
for two to three hours, when the pressure first rises to
twenty-five atmospheres and then falls again. The
product is neutralised with lime, and the base separated
by steam ; it then contains 90 per cent, of monom ethyl -
aniline arid 6 to 7 per cent, of dimethylaniline. Mono-
methylaniline boils at 192.
ALKYLATION 71
Monoethylaniline, C 6 H 6 .NH.C 2 H 5 , is prepared by
heating 95 parts of aniline hydrochloricle with 28 parts
of alcohol at 180 in an enamelled autoclave. The
hydrochloride of monoethylaniline crystallises out. The
base is a colourless liquid of B.P. 204.
Benzylaniline, C 6 H 5 .NH.CH 2 .C 6 H 5 , is obtained by
treating aniline with benzyl chloride. It is a solid,
and has M.P. 33 and B.P. 310.
Diphenylamine, C 6 H 5 .NH.C 6 H 5 , is prepared com-
mercially by the process of De Laire, Girard and Chapo-
teaut, in which aniline is heated with aniline hydro-
chloride in an autoclave at 220-230 :
C 6 H 5 NH 2 + C 6 H 5 NH 2 .HC1 = NH 4 C1 + (C 6 H 5 ) 2 NH.
The product is poured into water, and hydrochloric acid
added to dissolve the aniline, when the diphenylamine
crystallises out, the yield being 60-70 per cent. It forms
colourless crystals of M.P. 54 and B.P. 310.
Tertiary Amines.
Dimethylaniline, C 6
Commercial Preparation. Dimethylaniline was origin-
ally obtained by heating aniline hydrochloride (or
aniline and hydrochloric acid) with methyl alcohol at
230-235. At the present time sulphuric acid is used
instead of hydrochloric acid, and aniline, which is cheaper,
is used in place of aniline hydrochloride, when there is
not so great a possibility of the autoclave (enamelled or
otherwise) being attacked by the volatile acid. According
to J. Walter (Chem. Zty., 11)10, 641, ct seq.), the practical
details of the process are as follows : 80 kilograms of
aniline, 78 kilograms of methyl alcohol and 8 kilo-
grams of sulphuric acid (168 Tw.) are heated together
in an autoclave at 230-235 ; the pressure rises to
twenty-eight to thirty-two atmospheres, this pressure
being maintained for three hours, and then the autoclave
72 ORGANIC DYESTUFFS
is allowed to cool. On opening a valve, the gases
escape, and the alcohol carried forward is condensed in
a worm-condenser. The product is then forced by
means of compressed air into a distillation apparatus,
neutralised with caustic soda, and the bases separated
by steam distillation. The dimethylaniline is purified
by redistillation. The yield is 92 per cent, of the
theoretical.
Dimethylaniline is a colourless liquid of B.P. 198.
Commercial dimethylaniline often contains mono-
met hylaiiiline and unchanged aniline. The presence of
the latter may be detected by means of dilute sulphuric
acid, which dissolves the alkylated bases, but gives a
precipitate with aniline of the insoluble aniline sulphate.
The monomethylaniline is detected by mixing the pro-
duct with acetic anhydride, which woiild cause a rise
in temperature, whereas with pure dimethylaniline the
temperature would be lowered, due to its solution. The
monomethylaniline may be detected and estimated
by treating the product with nitrous acid in presence
of hydrochloric acid, and then with ether, when only the
nitroso-monomethylaniline dissolves.
Methylbenzylaniline is obtained by the action of
benzyl chloride on monomethylaniline. It is a liquid
of B.P. 310.
Ethylbenzylaniline boils at 285 (710 mm.).
Alkylated Derivatives of the Amidophenols.
Of these, the only ones important in the manufacture
of dyestuffs are those derived from ra-amidophenol ;
they are obtained by the alkaline fusion of the mda-
sulphonic acids of mono- and di-alkylated anilines.
Monomethyl-m-amidophenol, ^B^^ISTTTPIT Tho pro-
perties and preparation of this compound are outlined
in a patent of the B.A.S.F. (D.R.P. 48,151). Mono-
ALKYLATION 73
rnethyl-metanilic acid is fused with caustic soda. This
sulphonic acid may bo obtained either by sulphonating
monomethylaniline or by methylating metanilic acid.
NnCIT 3 NHCH 3
Monoethyl-m-amidophenol is obtained in a similar
manner. It crystallises, and has M.P. 02.
OTT
Dimctliyl-m-amidophenol, C 6 H 4 < X r /r i T j x , is prepared
by several processes, for example, by fusing dimethyl-
aniline sulphonic acid with alkalies (D.K.P. 44,792), or
by heating resorcinol in an autoclave with dimethyl-
ainiiic (D.R.P. 49 ,000). Dimethyl-w-amidophenol forms
small crystals which melt at 87.
OTT
Dicthyl-m-amidophenol, C 6 H 4 <^ X r /ri TT v , is obtained
in a similar manner to the dimethyl compound.
THIRD PART.
THE ORGANIC DYESTUFFS.
CHAPTER IX.
CLASSIFICATION AND APPLICATION OF
DYESTUFFS.
THE classic experiment with Newton's prism showed
that sunlight and white artificial light (from petrol,
gas, incandescent and arc lamps) are formed by the
superposing of coloured rays of light, the unequal
refraction of which causes their separation on passing
through the prism. The coloured image obtained in
this manner with a pencil of white light is known as
the "spectrum." Seven different shades may be dis-
tinguished : violet, indigo, blue, green, yellow, orange
and red, called fundamental colours, as by admixture
in suitable proportions all the various shades may be
produced.
A body is said to be transparent when light can pass
through it without being considerably diminished in
intensity ; on the other hand a body is termed opaque
when it does not allow light to pass through in this
manner. A body intermediate between these two is
known as a translucent body. In nature, the majority
of substances are opaque, and when light falls on
them it is more or less completely reflected into space.
The amount of reflection depends on the condition of
CLASSIFICATION AND APPLICATION 75
the surface, being greater the more polished is the
surface.
When light is reflected from a body, several things
may occur : (1) The object may reflect the sunlight
without altering the proportions of the different colours
in the spectrum, and the object will appear to be white ;
(2) the object may absorb entirely all the light which
it received, when it is called black ; or (3) the object
illuminated may only reflect a portion of the coloured
rays which form the white light, and absorb the other
portion. The object will then appear to be coloured.
Newton employed the term complementary colour to
denote the colour which together with the one to which
it is complementary would produce the effect known as
white.
Coloured substances are met with amongst the
chemical elements as well as in their compounds ;
thus iodine, sulphur, bromine, phosphorus, etc., are
coloured ; certain metals, for example, iron, chro-
mium, copper, and nickel, yield coloured salts ; others
generally give colourless salts. Compounds of the
so-called " organic " chemistry, that is to say, those
which result from the combination of carbon with
oxygen, hydrogen, nitrogen, or sulphur, are as a rule
colourless or white substances. It is, hence, very
curious indeed that there arc many organic compounds
which possess an intense and brilliant colour. By the
detailed study of these cases, it has been found that
analysis will only give a very small difference between
the percentage composition of a colourless organic com-
pound, and that of the highly coloured compound from
which it is derived. Moreover, examples are known
of coloured substances which have exactly the same
composition a*s others which are perfectly colourless.
Hence it is considered that the cause of these great
differences is mainly the manner in which the atoms are.
bound to one another ; briefly colour depends on the
structure of the molecule. To use a classic comparison,
76 ORGANIC DYESTUFFS
it is possible to construct several buildings of very
different types with a number of bricks ; and in the
same way the atoms of carbon, hydrogen, nitrogen,
oxygen, etc., may bo combined as to give an almost
unlimited number of compounds, the properties of which
may be very different. Certain compounds will be
colourless, others will be coloured, according to the
relative arrangement of the atoms. These arrangements
are represented by diagrams known as " constitutional
formulae," which, amongst other things, illustrate
clearly a relation between the colour of an organic
substance and the manner in which its constituent atoms
are linked. On examining the constitutional formulae
of coloured substances, the presence of certain atomic
groupings is noted, and consequently the colour is
attributed to then" presence.
In 1876, 0. N. Witt (Her., 9, 522 ; cf . ibid., 1888, 21, 325)
endeavoured to state a general theory for these pheno-
mena, and suggested that these special groups should be
termed " chromophores." In order that a chromophore
may be able to exert its influence, it must be present in
an organic substance which contains a large number of
carbon atoms, and it is hence that coloured substances
are more frequently met with among the derivatives
of hydrocarbons such as benzene, naphthalene and
anthracene, the so-called aromatic hydrocarbons. If
a chromophore is introduced into a molecule of an
aromatic organic compound, a substance which is more
or less coloured is obtained which Witt called a " chro-
mogen." Thus azobenzene, anthraquinone, and quinono
are chromogens, being coloured, due to the presence of
the chromophores :
-N=N-, CO, etc.
/co.
C 6 H 5 -N - N-C 6 H 5 CJV >C 6 H 4
CO
Azobonzene. Anthruquinouo.
CLASSIFICATION AND APPLICATION 77
Chromogens yield colourless compounds on reduction.
For example, azobenzene and quinone take up two atoms
of hydrogen and are decolorised :
C 6 H 5 -N=N-C 6 H 5 +H 2 = C 6 H 5 -NH-NH-C 6 H 5 ,
Azobenzene (coloured). Hydrazobenzeno (colourless).
C 8 H 4 2 + H 2 = C H 4 (OH) a
Quinone (coloured). Hydroquinonc (colourless).
These conversions are reversible, as hydrazobenzene
and hydroquinone yield on oxidation the coloured
substances from which they were obtained. In most
cases it is possible to convert a coloured substance in
this manner into a colourless one and vice versd ; such
reduction products are known as " leuco-compounds."
On the other hand, reduction sometimes completely
decomposes coloured substances, and the colourless
products do not yield the original substance on oxida-
tion ; such reduction products are no longer to be
regarded as leuco-compounds.
The disappearance of the colour, due merely to the
taking up of hydrogen by the chromophore, shows that
the relative affinities of the atoms which form it are not
entirely saturated, these affinities being latent. In
chemical language, this fact may be expressed by saying
that chromophores are " unsaturated," and in the
formulae the latent valencies are indicated by two or
three lines called " double " or " triple " bonds. Un-
saturated hydrocarbons are known which are coloured,
for example, H c C 6 H 4
I >0 = C/|
H 4 C/ \C 6 H 4
di-diphenylene-ethylene, which is red in colour. On
reduction, it takes up two atoms of hydrogen, giving the
colourless saturated hydrocarbon :
H 4 C 6 x /CeH 4
| >CH-CH<( |
H 4 C/ X C 6 H 4
78 ORGANIC DYESTUFFS
Cycle- pen tadiene
X CH - CH
CH/ I
CH-CH
combines with aldehydes to give the highly coloured
fulgides, which are compounds of the type :
-- CH
RCH = C< I
\CH - CH
the parent hydrocarbon of which is the coloured fulvene,
an isomer of the colourless benzene.
As a rule, however, it is necessary for the compound
to contain other elements than carbon and hydrogen,
such as oxygen, sulphur, or nitrogen.
Dyeing. The conditions necessary for an organic sub-
stance to be coloured have been outlined above, but, if a
substance is coloured, it is not of necessity a " dyestuff."
Every coloured substance which can be fixed on the
fibre in a more or less permanent manner by the processes
used in dyeing or printing is called a dyestuff. The
simplest way of dyeing fibre is to immerse it in a dilute
solution of the dyestuff (for example, 0-02 or 0-1 per cent.
aqueous solution), to which has been added an acid or
suitable salts, and then heating almost up to the boiling
point. In certain cases the dyestuff is precipitated on
the fibre and dyes it uniformly ; if the colour does not
disappear on washing with water the fibre is said to be
dyed. Dyed materials are more or less fast according to
the nature of the dyestuff and its affinity for the fibre in
question. This affinity varies considerably for different
dyestuffs, and the same dyestuff often has very different
affinities for different kinds of fibre. Whilst the majority
of soluble dyestuffs dye animal fibres (wool and silk)
under suitable conditions, there are only a comparatively
small number which dye vegetable fibres (cotton, linen,
jute, etc.) with equal facility. When the affinity of a
dyestuff for a certain fibre is not sufficient to give fast
CLASSIFICATION AND APPLICATION 79
shades the material is " mordanted." Mordanting
consists of fixing on the fibre a substance, known as a
mordant, which is capable of forming an insoluble
coloured compound, called a lake, with the dyestuff
at the time of dyeing, which hence remains fixed on the
fibre. The insolubility of these lakes renders them very
stable to the various mechanical and chemical treatments,
and hence shades obtained by the use of mordants are
very fast, and they are used whenever fast shades
are required. The natural colouring matters, such as
logwood, madder, and cochineal, which were used even
in the earliest civilisations, are mordant dyestuffs.
Mordants may be divided into " metallic mor-
dants " and "organic mordants." The former are the
hydroxides of certain metals, of which the most impor-
tant, owing to their frequent use, are ferric, aluminium,
and chromium hydroxides. These are the common
mordanting agents, others being the special mordants,
such as the oxides of zirconium, lanthanum, glucinum,
titanium, etc., studied by A. Scheurer and Brj^linski.
The same dyestuff gives very differently coloured lakes
with different mordants ; thus madder (Alizarin) gives a
red lake on aluminium mordant, a garnet-coloured lake
on chromium mordant, and a violet lake on iron mordant.
Hence, the name " polygenetic dyestuffs " is sometimes
given to those dyestuffs which are fixed by metallic
mordants.
The organic mordants include the different tannins, and
also fatty mordants, e.g. Turkey red oii, the exact action
of which in fixing the dyestuff is not as yet definitely
established. The principal organic mordant is tannin,
which is used for mordanting vegetable fibres. Tannin
possesses the property of forming lakes with a large
number of dyestuffs which themselves have no affinity
for vegetable fibres. It is therefore sufficient to mor-
dant the fibre with tannin, and then dye it in order
to cause the uniform precipitation of the coloured
lake. If vegetable fibres are immersed in an aqueous
80 ORGANIC DYESTUFFS
solution of tannin for a sufficient time, the cells become
impregnated with tannin. ; on subsequent immersion
in the bath containing the dyestuff, this penetrates
into the cellular membranes, forming an insoluble
lake inside the fibre, which will then be dyed. The
lakes so obtained are only comparatively insoluble, but
very fast coloured lakes may be obtained by combining
the dyestuff with both tannin and antimony oxide. For
this purpose the fibre is passed through a tannin bath
and then into tartar emetic ; after washing, the antimony
tannate remains on the fibre and acts as a mordant.
Soluble dyes tuffs may be divided into two groups :
those which dye textile fibres without the addition of
mordants, the " substantive " dyestuffs, and those
for which the use of mordants is essential, the " adjec-
tive " dyestuffs. The name " direct " or wt substantive "
dyestuffs has been reserved for dyestuffs which dye
cotton and vegetable fibres without the use of a mordant.
Whilst the dyeing of mordanted fibres is undoubtedly
due to a chemical combination, the dyeing of the same
fibres by means of substantive dyestuffs is a much more
complex phenomenon. In this case, the physical
phenomena of adhesion, capillarity, absorption and
contact electrification, are to be taken into account in
addition to the chemical phenomenon of combination
between the dyestuff and the fibre.
With regard to insoluble dyestuffs, their use necessi-
tates special methods which will be described when they
are being considered. (See Indigo, Sulphur colours,
Aniline black.)
The conditions which must be satisfied before a
coloured substance will act as a dyestuff will now be
considered. If the various dyestuffs which are soluble
in water are examined, it will be found that they are
all of the nature of salts ; some are produced by the
combination of an organic base with a mineral, or some-
times an organic, acid ; others consist of a coloured
organic acid combined with inorganic bases. The
CLASSIFICATION AND APPLICATION 81
first-named are called " basic dyes tuffs/' the latter are
termed " acid dyestuffs." In all dyestuffs one or other
of these two characters is invariably more or less
pronounced, and as a general rule it may be said that
the tinctorial properties of a dyestuff will be the greater
the more decided the acid or basic character. On the
other hand a neutral compound, in which these two
tendencies are balanced, will be a dyestuff of inferior
character. Hence, if suitable groups are introduced
into a coloured molecule, that is a chromogen, in order
to give it an acid or basic character, the product may be
expected to be a dyestuff. This has been found to be
the case, and Witt has given such groups the name
" auxochromes." Briefly : The introduction of a chromo-
phore into an organic molecule yields a coloured compound,
a chromogen, and this will yield a dyestuff if suitably chosen
auxochromes are introduced into certain positions in its
molecule.
The auxochromes are groups which are capable of
salt-formation, such as OH, S0 3 H, COOH, which are
acidic, and NH 2 , NHR, NR 2 , which are basic. Of these
auxochromes, the COOH and SO 3 H groups introduced
into a chromogen generally give it tinctorial properties
without altering its shade. It has, however, been shown
by Friedliinder that the S0 3 H group causes a great change
in the shade of Indigoid dyestuffs if present in a certain
position. On the other hand, the presence of the acidic
OH group, or of the basic NH 2 , NR 2 groups, has a very
decided effect on both the tinctorial properties and on
the shades of the product.
After what has been noted above, it does not seem
impossible that textile fibres should also have a certain
affinity for organic substances which are not coloured ;
in other words, it is possible to imagine that colourless
substances might just as well be fixed on the fibre by
" colourless dyeing/' It has actually been found that
cotton and vegetable fibres possess a very decided affinity
for tannin, and also for the anilide of /i-oxynaphthoie
82
ORGANIC DYESTUFFS
acid ; on immersion in a warm, dilute solution of
chromotropic acid, wool absorbs this compound as it
would a dyestuff.
Chromophores.
The chromophores are very numerous, and have a more
or less pronounced effect on the colour. They are almost
all unsaturated groups and consequently polyvalent ;
only the nitro-group, NO 2 , is monovalent, and reduction
completely destroys it without giving a leuco-compound.
One of the commonest chromophores is the carbonyl
group, CO, present in quinone. Quinone, C 6 H 4 2 , is a
yellow compound which on reduction gives the colourless
hydroquinone, C 6 H 6 O 2 ; the reaction is a reversible one,
hydroquinone yielding quinone on oxidation in acid
solution : jf o
C 6 H 4 2 ^_ C 6 H 6 O 2
These reactions are supposed to be accompanied by a
change in the linking of the atoms, expressed by :
o OH
ii i
o c
H 9 =
OH
Thus hydroquinone is the " leuco-derivative "of quinone.
An attempt has been made to classify the reduction
of dyestuffs to leuco-compounds, and their production
again on oxidation of the leuco-compounds, according to
a method similar to the above example. That is to say,
a group identical with or very similar to that in quinone
is supposed to be present in coloured molecules. Two
types of quinones are known : or/Ao-quinones and para-
CLASSIFICATION AND APPLICATION 83
quinones, dyestuffs being termed or/io-quinonoid or para-
quinonoid, according to the grouping which is present.
KG
o-Benzoquinone. >-Benzoquinone.
The Quinonoid theory of dyestuffs was suggested by
Nietzki, but was first applied to coloured organic sub-
stances by Armstrong. It has the advantage of illustrat-
ing clearly the difference between the structure of a dye-
stuff and that of its leuco-derivative ; it also illustrates
the unsaturated character of the chromophores, and the
influence exerted by the position occupied by the auxo-
chromesinthemolecule, these being generally or tho or para.
The recent researches of Willstatter, however, have
shown that certain dyestuffs owe their colour to the
combination of the quinonoid molecule with its reduction
product, and hence belong to the " quinhydrones."
Quinhydrone is the product obtained by the addition
of one molecule of quinone to one of hydroquinone ;
it is highly coloured, and, admitting the tetravalence
of oxygen, may be represented by the formula :
HO
OH
(Richter, Ber., 1910, 43, 3603).
84
ORGANIC DYESTUFFS
The various dyestuffs have been classified according
to the chromophore present :
Chap. X. Nitro-dyestuffs.
XI. Nitroso-dyestuffs or Quinone-oximes.
,, XII. Azo-dyestuffs.
,, XIII. Hydrazones.
XIV. Stilbene dyestuffs.
XV. Diphenylmethane dyestuffs.
,, XVI. Triphenylmethane dyestuffs.
XVII. Xanthene dyestuffs.
XVIII. Acridine dyestuffs.
,, XIX. Anthracene dyestuffs.
XX. Quinone-imide dyestuffs (Indamines, Inclo-
phenols, Oxazines, Thiazines, Azines).
XXI. Indigo and indigoid dyestuffs.
XXII. Thiazol dyestuffs.
XXIII. Sulphur dyestuffs.
f> XXIV. Aniline black.
CHAPTER X.
NITRO-DYESTUFFS.
THE iiitro-dyestuffs contain the chromophore NO 2 ;
the niononitro-derivatives of the hydrocarbons are
colourless or slightly coloured, but the intensity of the
colour increases with the number of nitro-groups intro-
duced. In order to convert these chromogens into dye-
stuffs, it is necessary to introduce auxochrome groups.
The character of the groups to be introduced is readily
decided by the following considerations.
The nitro-chromophore gives an acid character to mole-
cules in which it is present, and it has been seen that the
tinctorial properties of a dyestuff will be better the more
pronounced its acid or basic character. Hence, it is
preferable to introduce auxochromes such as OH, SO 3 H,
whose acid character will then be added to the effect of
the chromophore itself. On the other hand, basic auxo-
chromes, such as NH 2 , NHR, NR 2 , will have their
influence opposed by the acidity of the NO 2 group, and
the tinctorial power of the product will be diminished.
In this case it is necessary to increase the acidity by
introducing a sufficient number of nitro-groups. It is
for this reason that the majority of the nitro-dyestuffs
are iiitro -derivatives of the phenols or naphthols, or their
sulphonic acids. The mono-nitrophenols give coloured
salts, but they do not behave as dyestuffs, tinctorial
powers only appearing with the di- or tri-nitrophenols.
The relative position of the OH and NO 2 groups has a
great influence, being most favourable when they are in
86 ORGANIC DYESTUFFS
ortho- or jpara-position ; thus these dyestuffs may be
considered as derivatives of ortho- or^ara-nitrophenol.
Victoria orange is a mixture of the potassium salts
of dinitro-o-cresol and dinitro-j>-cresol, obtained by the
nitration of the cresol sulphonic acids. It dyes wool
and silk a yellow colour.
Flavaurine or New yellow is the 1:2:6: 4-dinitro-
phenol sulphonic acid, obtained by the nitration of
o-nitrophenol ^p-sulphomc acid.
Picric acid is the 1:2:4: 6-trinitrophenol :
OH
It is the oldest of the artificial dyestuffs. It is obtained
by treating a large number of organic substances, such
as hide, skin, aloes, etc., with nitric acid. Woulfe
prepared it in 1771 by the action of nitric acid on Indigo,
and noticed that it had the property of dyeing silk
a yellow colour. In 1799, Welter prepared it in a
crystalline condition by the action of nitric acid on wool
and on silk. Its very bitter taste caused it to be given
the name " Welter's bitter yellow " or " picric acid "
(from TrtK-pos, meaning "bitter"). Laurent showed
in 1842 that it is a trinitrophenol.
Picric acid may be prepared by the nitration of phenol
and of a large number of its derivatives, such as o-nitro-
phenol, p-nitrophenol, dinitrophenol, and phenolsul-
phonic acid. The last mentioned has been employed
by Schmidt and Glutz (Mon. Sci. 9 1878, 1115), and is
used commercially. The apparatus employed is similar
to that used in the manufacture of nitrobenzene. Equal
parts of phenol and sulphuric acid (sr. GR. 1-84) arc
mixed and heated to 100. Under these conditions,
phenol p-sulphonic acid is produced, and to this an
JNITKO-JWYJUSTUJ^S 87
excess of nitric acid is added with constant stirring.
On cooling, the product forms a crystalline mass, which
is separated, washed with water, and purified by re-
crystallisation. The action of nitric acid on phenol
sulphonic acid is as follows :
OH OH
C 6 H 4 / + 3HN0 3 = C 6 H 2 <^ + H 2 S0 4 + 2H 2 0.
S0 3 H (N0 2 ) 3
Picric acid crystallises in yellow plates of M.P. 122-5,
which are slightly soluble in cold water, but are more
soluble in warm water and in alcohol. It forms coloured
salts, the potassium salt being remarkable for its slight
solubility in water. On treatment with alkaline reducing
agents, such as ammonium sulphide, picric acid readily
gives picramic acid, dinitro-amidophenol, which is used
for the manufacture of certain azo-dyestuffs.
OH
On treating potassium picrate with a solution of
potassium cyanide, an intense red coloration is pro-
duced, due to the % formation of isopurpuric acid. The
ammonium salt of this acid was for some time used under
the name of Orenat soluble for dyeing wool and silk
a reddish brown. Picric acid may also be used for
dyeing wool and silk yellow, but the shades obtained
are not very fast to washing or to light Hence, picric
acid is rarely used except in small quintities in ad-
mixture with other dyestuffs. On the o t :her hand, its
explosive properties make it an important raw material
for the preparation of explosives. It is introduced into
shells in the molten state, being termed "' melinite " ;
" lyddite," " roburite," etc., are similar products.
88 ORGANIC DYESTUFFS
Martins yellow, or dinitro-a-naphthol,
on
This dyestuff has also been called Manchester yellow,
Naphthylamine yellow, or Naphthalene yellow, and was
prepared commercially by Martins (E.P. 2785 (1864) ),
by treating a-naphthol or a-diazonaphthalene with
nitric acid. It is also formed on the nitration of
a-naphthylamine, nitrosonaphthols, and 1:2: 4-naphthol
disulphonic acid. This last-mentioned process is the
method used in commerce (Darmstatter and Wichelhaus,
Ann., 1869, 152, 299) ; the snlphonic groups are replaced
by nitro-groups, giving the dinitro-a-naphthol.
Martius yellow crystallises in yellow needles of M.P.
138 ? . Its alkali salts are very stable, as it is a strong
acid, even decomposing carbonates. It dyes wool and
silk a bright yellow, which is not very fast to washing or
to heat on account of its volatility. Its main use was
in the colouring of edible pastes (vermicelli and macaroni),
for which purpose Naphthol yellow S is now used.
Naphthol yellow S.
OH
S0 3 H
NO 2
This dyestulf is also known as Acid yellow, Citronine A,
etc. It is tb3 sulphonated derivative of Martius yellow,
and is obtained by the nitration of a-naphthol tri-
sulphonic acid (1:2:4:7), when the sulphonic groups
occupying positions 2 and 4 are replaced by nitro groups
(B.A.S.F., DM.P. 10,785, Dec. 28th, 1879). Another
NITRO-DYESTUFFS 89
method of preparation is to sulphonate a-naphthol in
such a manner as to give a mixture of the 1:2:7 and
1:4:7 naphthol disulphonic acids, which is then
treated with nitrous and nitric acid (D.R.P. 20,716).
The salts of Naphthol yellow S have been described by
Knecht and Hibbert (Ber., 1904, 37, 3475). The
commercial product is the potassium salt, which dyes
wool and silk a brilliant yellow.
Aurantia is the hexanitro-derivative of diphenyl-
ainine :
(N0 2 ) 3 C 6 H 2 NH C 6 H 2 (N0 2 ) 3 .
Hexanitro-diphenylamine was discovered in 1873 by
Kopp, who called it c * Kaisergelb." It crystallises from
acetic acid in lemon yellow prisms of M.r. 238.
The basic character of the diphenylamine is overcome
by 1he acidity of the six nitro-groups present in the
molecule, and hence hexanitro-diphenylamine behaves
as an acid in which the hydrogen attached to nitrogen
is replaceable by metals to form salts. Its salts are
highly coloured. The commercial product is the am-
monium salt, which crystallises in brownish red needles.
Aurantia dyes wool and silk an orange colour, but has
not been used since the discovery of the azo-dyestuffs.
Constitution of the Nitro-Dyestuffs.
It is known that the introduction of a mtro-group into
a hydrocarbon molecule gives acid properties to the
atoms of hydrogen attached to the same carbon atom.
It is for this reason that nitromethane, nitroethane,
phenylnitromethane, etc., dissolve in alkalies to form
true salts. V. Meyer first stated that in these salts the
metallic atom is substituted for hydrogen and hence
directly linked to carbon :
CH 3 CH 2 NO 2 -> CH 3 CHNa NO 2 .
The study of these derivatives showed that the alkali
90
ORGANIC DYESTUFFS
salts are related to an isomeric form of the nitro-com-
pound, which is formed when salt-formation occurs.
These tautomeric forms were called " iso-nitro-" com-
pounds, and a certain number of iso-nitro-compounds
have since been isolated whose constitution is expressed
by:
R . GEL NO,
Nitro.
R CH = N
O
OH
Jso-nitro.
The nitrophenols form two series of salts with alkalies,
a colourless series and a coloured series. Hantzsch
(Ber., 1906, 39, 1084, 3072) has explained this fact by
regarding the coloured salts as derivatives of iso-nitro-
compounds, called " aci-nitrophenols."
OH
o
HC
HC
CH
CH
HC
CH
HC
CH
O N OH
As will be seen from the third formula (quinone),
aci-nitrophenols are derivatives of quinone. The same
holds good for all the dyestuffs of this group.
CHAPTER XL
NITROSO-DYESTUFFS OR QUINONE-OXIMES.
WHEN nascent nitrous acid acts on phenol, a nitroso-
derivative is formed in which the nitroso-group occupies
the para- or ortJio-po&ition :
o
OH OH
HNO 2 = H 2 O -f
(I.) NO
The nitrosophenols are also obtained by the action
of hydroxylamine on the quinoiies, and hence nitroso-
phenols may be considered as oximes of the quinoiies ;
hence the name quinone-oximes. The true nitroso-
phenol (I.) can change immediately into the oxime of
quinoiie (II.). The fact that nitrosophenols are con-
verted into dioximes by hydroxylamine, constitutes
another proof in favour of formula II. There are, how-
ever, jp-quinone oximes and o-quinone oximes ; these are
coloured substances the salts of which possess an even
more intense colour. The o-quinone oximes have the
property of forming insoluble lakes with metallic oxides,
i.e. they are dyestuffs which dye on metallic mordants,
the commonest mordant being ferric hydroxide, which
gives intense green shades. The most important dye-
stuffs of this group are :
92
ORGANIC DYESTUFFS
Dinitroso-resorcinol, obtained by treating an aqueous
solution of resorcinol with nascent nitrous acid. It
crystallises in brown plates of M.P. 115, and has the
following constitution :
NOH
It gives olive green shades on iron mordant, and
comes into commerce under the names Fast green,
Russian green, Alsace green.
Nitrosonaphthols are produced on treating naphthols
with nascent nitrous acid : /2-naphthol gives a-nitroso-
/3-naphthol (I.) ; a-naphthol gives two nitroso-com-
pounds, /?-nitroso-a-naphthol (II.) and a-nitroso-a-naph-
thol (III.).
NOH
O
= NOH
NOH
(III.)
Compound I. is called Gambin G or Y, and compound
II. is known as Gambin R ; they are commercial in
the form of pastes, and both give green shades on iron
mordant. On treatment with nitrite, 2 : 7-dihydroxy-
naphthalene gives Dioxin. Naphthol green is obtained
in a similar mariner from Schaffer's /3-naphthol mono-
sulphonic acid.
NITROSO-DYESTUFFS 93
p 'Nitrosodimethylaniline, NO C (; H 4 N( CH 8 ) 2 .
Tertiary amines also react with nascent nitrous acid
to give nitroso -derivatives, which are not dyestuffs, but
are important intermediate products. Nitrosodimethyl-
anilirie is prepared as follows : 200 grms. of dimethyl aniline
are dissolved in 500 cc. of ^hydrochloric acid diluted with
500 or 600 cc. of water, and a concentrated aqueous solution
of 115 grm. of sodium nitrite added slowly from a tap;
funnel immersed in the liquid. The vessel in which the
reaction is carried out is immersed in a freezing -mixture
of ice and salt, and it is advisable that the temperature
should not rise above 5 to 10. Nitrosodimethylaniline
hyclrochloride is precipitated in small yellow needles, which
are separated, washed with a small amount of water, and
dried at a low temperature. For almost all purposes, the
hydrochloride may be used instead of the free base, which
is obtained on decomposing with an alkali, and forms green
crystals of M.P. 85.
Dimethyl -p -phenylen ediamine, NH C 6 H 4 N( CH 3 ) 2 .
The hydrochloride of the above compound may be
used directly for the preparation of this important
diamiiie. Fifty grm. of nitrosodimethylanilinQ hydro -
chloride are added to a cooled mixture of 150 cc. of con-
centrated hydrochloric acid and 50 grm. of granulated tin.
The nitrosodimethylaniline dissolves, and the solution,
wliich is slightly coloured, or even colourless if the tempera-
ture has been kept sufficiently low, is left for twenty-four
hours. The stannichlorido of the diamine is precipitated
in dense crystals, which are separated, decomposed with
concentrated caustic soda, and allowed to cool. The
diamine separates as an oil wliich rapidly turns brown on
exposure to air ; it is extracted with benzene, the benzene
solution separated, washed, and concentrated. The residue
is then distilled in vacuo, and yields dimethyl ->-phenylene-
diamine as a colourless liquid which solidifies to a white
crystalline solid of M.P. 41, B.P. 262-3.
CHAPTER XII.
AZO-DYESTUFFS.
THE azo-compounds contain the chromophore
N=N .
On treating the salt of a primary aromatic amine with
nascent nitrous acid, a " diazo-compouiid " is formed,
as follows :
R NH 2 .HC1 + HNO 2 = 2H 2 O + R N=N Q.
The diazo-compounds are generally colourless ; they
combine with amines and phenols derived from benzene
and naphthalene or their substitution products (nitro-,
sulphonated, halogenated, etc., compounds), giving rise
to numerous intense dyestuffs of various shades.
Historical. The action of nitrous acid on primary
amines is called " diazotisation " and was discovered by
P. Griess, who showed, in 1864, that diazo-compounds
combine with amines. Later it was shown by Kekul6
and Hidegh that they also combine with phenols. Before
Griess had recognised the wide application of his method,
amidoazobenzene, Aniline yellow, had already been
prepared by the action of nitrous acid on aniline (1859).
In 1865 Martius applied the diazo-reaction to diamines,
particularly ra-phenylenediamine, which gives a brown
dyestuff, Bismarck brown, which has been prepared
commercially since 1866. In 1875, Caro and Witt
combined the diazo-compounds of primary amines with
diamines, and obtained the Chrysoidines. About the
same time, Roussin in France, and Griess and Witt in
AZO-DYESTUFFS 95
England, prepared Orange I. and //., in which the
naphthols, which were then much more difficult to
obtain, were used for the first time.
From this time the number and variety of azo-
dyestuffs rapidly increased ; the sulphonic acids of
various amines were diazotised and combined with the
numerous isomeric sulphonic acids of the naphthols
and naphthylamines. Thus, in 1878, there appeared
the Ponceaux of the Hochst Farbwerke (Meister, Lucius
and Bruning), the Orchil substitutes of Roussin and
Poirrier, etc.
Azo-dyestuffs which contain an amido-group may
be diazotised to yield new dyestuffs containing two
N=N chromophores ; these are called " disazo-
compounds," the first of which, Biebrich scarlet, was
prepared by Nietzki in 1879. In this manner the
possible number of compounds was considerably in-
creased. A notable discovery was made in 1884 by
Boettiger, who tetrazotised benzidine (produced by the
molecular change of hydrazobenzene in presence of acid :
C 6 H 5 -NH-NH-C 6 H 5 -> NH 2 . C 6 H 4 -C 6 H 4 .NH 2 ),
and combined with naphthionic acid, when a red
dyestuff was obtained which dyed cotton directly,
whereas all the azo-dyestuffs known previously only
dyed animal fibres. This dyestuff, called Congo red,
was prepared by the Berlin Aktiengesellschaft. Benzi-
dine and its various homologues yield innumerable
dyestuffs on combining with naphthol sulphonic acids.
In 1887 Green discovered a new series of substantive
dyestuffs derived from Primuline. Certain of these dye-
stuffs may even be prepared directly on the fibre. This
resulted in the introduction of a new practical process
in dyeing, that of the " Ingrain " dyestuffs, which led
to the direct production of insoluble azo-dyestuffs on
the fibre, such as Paranitr aniline red, a-Naphthylamine
bordeaux, etc. By still further complicating the molecule
of the azo-compound, trisazo- and polyazo-eompounds,
96 ORGANIC DYESTUFFS
containing the chromophore three or four times, are
obtained. Brown and black dyestuffs for wool and for
cotton have also been prepared.
At present these complicated methods are being
abandoned and the monoazo-derivatives of substituted
o-amidophenols are again being largely used ; these yield
mordant dyestuffs, which are applied in a particular
manner. The wool is dyed as usual, and then treated
with a solution of potassium dichromate, when the shade
undergoes a remarkable change ; it darkens, and becomes
very fast ; very resistant blacks may be obtained in
this way. They are termed "" chrome-developed " or
" after-chromed " Azo-dyestuffs.
The azo-dyestuffs known at present number many
thousands, but they only represent a small fraction of
the number possible according to theory, Biilow having
calculated that about 3,160,000 may exist.
Preparation of Azo-compounds.
The production of azo-compounds includes several
operations :
1 . The diazotisation of the primary amine ;
2. The combination of the diazo-compound with an
amine or a phenol, often called coupling ;
3. The precipitation of the dyestuff from the solution
in which it has been formed.
The conditions under which the various operations
should be carried out were described in the English
patent taken out by Griess on October 4th, 1877 (identical
with D.R.P. 3224).
1. Diazotisation.
In this process the salt of an amine is converted into
the corresponding salt of the diazo-compound by the
action of nascent nitrous acid, produced by the decom-
position of sodium nitrite with dilute hydrochloric acid :
K_NH 2 .HC1 + NaNO 2 + HC1
= NaCJ + 2H 2 + R . N = N . 01.
AZO-DYESTUFFS 97
Compounds which are true salts contain pentavalent
nitrogen, and are called tfc diazonium salts " :
R N Cl
N
This reaction is generally quantitative and rapid,
often instantaneous. When a simple amine, such as
aniline or o-toluidine, is being diazotised, it is essential
to add a large excess of mineral acid. If this precaution
is not taken, a secondary reaction occurs, due to the
combination of the diazo-compound produced with a
portion of the original amine. In the case of aniline,
diazoamidobenzene would be formed, thus :
C 6 H 5 .N=N.C1 + H 2 N.C 6 H 5
= HC1 + C 6 H 5 . N =N . NH . C 6 H 5 .
The presence of this compound is shown by the yellow
colour of the solution and the formation of a yellow
precipitate. This secondary reaction is avoided by
keeping the solution sufficiently acid, by adding three or
four equivalents of hydrochloric acid instead of the two
theoretically necessary.
Diazotisation should take place at a low temperature,
about 0, as diazo-compounds are more or less decomposed
on heating their solutions. Certain diazo-compounds
decompose even at several degrees above ; others,
on the other hand, are stable up to about 100 (e.g.
the diazo-compound of Primuline). The decomposition
takes place with liberation of nitrogen, and phenol is
produced :
C 6 H 5 .N=N.C1 + H 2 O = HC1 + N 2 +C 6 H 5 OH.
Hence this constitutes a method for preparing a
phenol from an amine.
In actual practice, the dilute solution of the amine
to be diazotised in the necessary amount of mineral acid
(two, three or four equivalents) is poured into a tank
O.D. G *
98
ORGANIC DYESTUPFS
fitted with a mechanical stirrer (Fig. 4). This solution is
cooled with ice, or in more perfect plants by the circula-
tion of brine, cooled to - 10 by an ice-machine, in a
coil immersed in the tank. When the temperature
is low enough, the sodium nitrite solution is run in
slowly, thQ process being followed by means of starch-
iodide paper (zinc iodide is preferable to potassium
A. Sodium nitrite.
(7. Diazotising vessel.
E. Compressor.
B. Gauge for measuring the nitrite.
1). Vessel for coupling.
F. Filter press.
iodide, as its antiseptic properties prevent the alteration
of the starch). Excess of nitrite is detected by the
production of a deep violet colour when a drop of the
solution is placed on the paper.
When amines , of which the salts are only slightly soluble ,
are to be diazotised, such as naphthylamines, benzidine,
etc., they are finely powdered, and then suspended in
dilute acid ; addition of nitrous acid causes their solu-
tion, owing to the formation of the diazo-compound.
AZO-DYESTUFFS 99
2. Coupling.
This process is carried out somewhat differently
according to whether it involves combination with a
phenol, a naphthol, or orie of their sulphonic acids, or with
an amine. In the first case (phenols, naphthols, and their
sulphonic acids) coupling is carried out in alkaline
solution. For this purpose the product is dissolved in
an excess of caustic soda or sodium carbonate, arid the
diazo-solution prepared as above is added, the excess
of alkali being sufficient to keep the liquid alkaline. In
the case of an amine, it is dissolved in dilute acid, and
coupling is effected in neutral or acid solution ; amido-
sulphonic acids are dissolved in alkalies, and the reaction
is carried out in neutral or acetic acid solution.
In commerce, the product to be coupled is dissolved
in a suitable manner, and its solution placed in a vat-
situated at a lower level than that which contains the
diazo-solution, to which it can be added. The vat is
fitted with a mechanical stirrer which stirs the liquid
throughout the process. The formation of the dyestuff
commences immediately at a more or less rapid rate, and
is often accompanied by the evolution of a considerable
amount of heat. The mixture is allowed to stand for some
time, and the reaction then completed by warming gently.
3. Precipitation of the Dyestuff.
The dyestuff does not often separate of itself, but is
precipitated by addition of salt, the method recommended
by Griess. Sometimes, when the free acid of the dyestuff
is insoluble in water, it is precipitated by addition of
mineral acid. These methods are general, and may
be applied in all cases. In commerce, common salt
is added to the warm solution of the dyestuff, and is
dissolved rapidly by stirring ; the dyestuff soon separates
in a more or less dense granular powder. The progress
of the reaction is followed by spotting the liquid on
filter-paper, when the precipitate is surrounded by a more
100 ORGANIC DYESTUFFS
or less coloured ring ; when the intensity of this colour
no longer decreases, the addition of salt is stopped. The
stirring is continued until the liquid is quite cold, and
then the liquid is treated in a filter-press as for the
separation of the sulphonic acids (see p. 27). The
cakes obtained are then placed in a drying-oven. These
ovens are brick chambers, heated by steam coils ; in
them are placed the trays containing the dyestuff to
be dried. This method of drying is rather long, and the
use of vacuum ovens is now preferred. The trays
containing the precipitate are placed in a pile in a hori-
zontal cylinder, which can be hermetically sealed. Steam
pipes arranged at the bottom may be used for raising
the temperature of the inside of the vessel, which is
evacuated by means of a pump.
After drying, the dyestuff is powdered in mills, of
which there are many types. One of the simplest
consists of a horizontal cast-iron cylinder, which can be
rotated round its axis, and in which the dyestuff to be
ground is placed. After rotating for one or two days,
the dyestuff is reduced to an mpalpable powder. The
final process consists in bringing the dyestuff to the
" commercial standard," that is to say, the concentration
desired for the market. For this purpose, comparative
dye-trials are made, and the necessary dilution is made
by adding the necessary amount of salt, sodium sulphate,
dextrine, etc.
CLASSIFICATION OF AZO-DYESTIWS.
According to whether an azo-compound contains one
or more N =N chromphores, it is called a monoazo-,
disazo-, trisazo- or polyazo-compound.
MONOAZO-DYESTUFFS.
The simplest monoazo-compourid is azobcnzene :
t C 6 H 5 -N=N-C 6 H 5 .
AZO-DYESTUFFS 101
This is a red substance, but has no dyeing properties.
It is a chromogeii of great importance, and it is
only necessary to introduce salt-forming groups (auxo-
chromes) to obtain dyestuffs. Its sulphonic acid is
a weak dyestuff, possessing a slight affinity for wool.
The ainido-, alkylamido- and hydroxy-derivatives of
azobenzene are dyestuffs ; they are prepared by the
action of any diazo-compouncl on an amido- or hydroxy-
compound. The monoazo-dyestuffs may hence be repre-
sented by the general formula :
X N-NY
in which X represents the radicle of the amine used for
the preparation of the diazo -compound and Y the radicle
of the amine or phenol which has been coupled with
this diazo-compound.
Properties. The monoazo-compounds have an acid
or basic reaction according to the nature of the auxo-
chromes present ; those derived from phenols or their
sulphonic acids are soluble in alkalies. The alkaline
solution often has a different colour from that of the
original substance ; this property is applied in the use
of indicators, e.g. Methyl orange. Concentrated sulphuric
acid dissolves azo-compounds, yielding coloured solu-
tions. Concentrated nitric acid decomposes azo-com-
pounds, and this has been used to ascertain their con-
stitution (Schmidt, Ber., 1905, 38, 3201). Thus :
S0 3 H . C 6 H 4 . N =N . C 6 H 4 . N(CH 3 ) 2 + 2HN0 3
S0 3 .C 6 H 4 .N-N + (N0 2 ) 2 C 6 H 3 . N(CH 3 ) 2 + 2H 2 O.
Chlorine, bromine and hypochlorous acid also de-
compose azo -dyes tuffs. In aqueous solution hydroxyazo-
benzeno gives with chlorine 2:4: (5-trichlorphenol
and benzene diazonium chloride (Schmidt, J. prakt.
Chem., 89, 239).
One of the most important reactions is that of reducing
102 ORGANIC DYESTUFFb
agents, which completely destroy the dyestuff, as
follows :
X N =N Y + 4H = X . NH 2 + NH 2 . Y.
The amine from which the diazo-compound was pre-
pared is regenerated, and the compound Y, which was
coupled with the diazo-compound, is converted into an
amido-derivative. This reaction may serve for the
determination of the composition or even the constitution
of azo-dyestuffs (Witt, Her., 1886, 19, 1719 ; 1888, 21,
3471). The most convenient reducing agents are : zinc
and hydrochloric acid, zinc and ammonia, zinc and
caustic soda, tin and hydrochloric acid, stannous chloride,
titanous chloride (Knecht and Hibbert,. Ber., 1905, 38,
3318), and sodium hydrosulphite (Grandmougin, Ber.,
1906, 39, 2494, 3561, 3929).
The monoazo-dyestuffs will be considered in two
groups :
1. Those formed by the combination of the diazo-
compound of any amine, X . NH 2 , with a hydroxy- or
amido-derivative of a benzene hydrocarbon. In this
case Y will represent an amine, a phenol, or one of their
derivatives.
2. Those formed by the combination of any diazotised
amine with a hydroxy- or amido-derivative of naphtha-
lene ; in this case Y will represent a naphthylamine, a
naphthol, or one of their sulphonic acid or other deriva-
tives.
When Y is a hydroxy-compound, the azo-compound is
called a hydroxyazo-compound ; when Y is an amine,
the azo-compound is called an amidoazo-compound.
Monoazo Derivatives of Benzene.
Constitution. The combination of a diazo-compound
\vith a# amine is governed by a certain number of rules :
I. Coupling takes place in the" /jam-position to the
auxochrOme groups, OH, NH 2 , NR 2 , when this is free.
AZO-DYESTUFFS 103
II. If the ^ara-position is occupied, coupling occurs
in the ortho -position.
III. If both ortho- and para- positions are occupied,
coupling does not occur.
Note. These rules have several exceptions. Cases
are known in which the ^&ra-position is occupied, but
coupling will not take place, although the ortho-position
is free. Thus, dimethyl-^-toluidine, dirnethyl-^-brom-
aniline, and dimethylsuiphanilic acid do not combine with
diazo-compounds (Scharwin and Kaljanow, Ber., 1908,
41, 2058). In other cases, when the ^ara-position is
occupied by an unstable group, this group may be
eliminated during coupling, which then takes place in
2>ara-position. For example, p-hydroxybenzoic acid, di-
methyl-^-amidobenzoic acid, and even tetramethyl-
diamidodiphenylmethane, combine in ^ara-position with
diazo-compounds, with elimination of carbon dioxide
and formic acid (Limpricht and Fitze, Ann., 1891, 263,
236).
Hydroxyazo-compounds .
The simplest compound of this class is hydroxyazo-
benzene : ^ N =N (j^ . OH
It is prepared by combining a diazonium salt with
phenol in alkaline solution, or by condensing aniline
with nitrosophenol. It crystallises in orange needles
of M.P. 151. On treatment with fuming sulphuric acid,
it gives a monosulphonic acid :
S0 3 H.C 6 H 4 .N-N.C 6 H 4 .OH,
which may also be obtained by coupling diazo-sulph-
anilic acid with phenol. Its sodium salt is called
Tropceolin 7, which dyes wool a rather dull brownish
yellow.
Diliydroxyazobenzenes. Sy in metrical dihydroxyazo-
benzene is known, being obtained by oxidation of the
corresponding hydrazo-compound, but it is not of any
104 ORGANIC DYESTUFFS
importance. The asymmetrical dihydroxyazobenzene is
obtained by combining a diazonium salt with resorciiiol ;
fuming sulphuric acid converts it into the
acid :
OH
which is also obtained by coupling diazo-sulphanilic
acid with resorcinol. The sodium salt is called Tropceolin
or Eesorcin yellow. It dyes wool a reddish yellow
shade.
A midouzo -compounds .
AMIDOAZOBENZENE, the first member of this series, is
obtained by a peculiar reaction, namely the molecular
change of diazoamidobenzene in presence of an excess
of aniline. One equivalent of aniline hydrochloride is
dissolved in five or six equivalents of aniline ; to this
mixture, warmed to about 30-40, is added a concentrated
solution of a little more than one equivalent of sodium
nitrite. After standing for two hours at 40, and then
for twelve hours at the ordinary temperature, an excess
of hydrochloric acid is added. Amidoazobenzene hydro-
chloride is precipitated in black needles. It was used
under the name of Aniline yellow from 1861-3 for dyeing
wool. It is now used as the raw material for the pre-
paration o/jp-phenylenediamine, which is obtained by
reduction (see Schultz, Chemie des /Steinkohlenteers, i., 87) :
C 6 H 5 . N =N . C 6 H 4 . NH 2 + 4H
= C 6 H 5 NH 2 + C 6 H 4 (NH 2 ) 2 .
On treatment with fuming sulphuric acid, this com-
pound gives a mixture of the mono- and di-sulphonic
acids, the sodium salts of which are known as Acid
yellow G, New yellow 9 or Fast yellow (for details see
Wiirtz, Dictionnaire de chimie, article on " Colorantes
(matieres)," p. 1313 in 2nd supplement).
AZO-DYESTUFFS 105
Dimethylamidoazobenzene,
C 6 H 6 N =N-C 6 H 4 -N(CH 3 ) 2 ,
is obtained by combining a diazonium salt with di-
methylaniline ; the free base crystallises in yellow plates,
and is used for colouring butter ; the hydrochloride
forms violet needles. The sulphonic acid, produced by
the combination of diazosulphanilic acid with dimethyl-
aniline, is called Helianthin. Its alkaline salts are
called Orange III. [P.], Tropceolin D, and Methyl
orange. They dye wool yellow, and are used as indi-
cators.
Phenylamidoazobenzene,
C 6 H 5 -N =N-C 6 H 4 -NH-C 6 H 5 .
The sulphonic acid of this compound was discovered
almost simultaneously by Witt, Griess and Roussin
(1870-7), by coupling diazo-sulphanilic acid with
diphenylamine. The alkali salts have the names
Orange IV. [P.], Diphenylamine orange, Neiv yellow, etc.
In the same manner, diazometanilic acid yields Metanil
yellow, the shade of which is more yello\v. By nitrating
Diphenylamine orange, Knecht has obtained the nitro-
derivatives : Azo yellow, Azoflavine ti, Indian yellow,
Citronine, etc.
DIAMIDOAZOBENZENE. Symmetrical and asymmetrical
derivatives are known, the latter being the more impor-
tant.
Chrysoidine,
C.H 8 -N = N-C 6 H 3
was discovered by Caro and Witt in 1875-6 by coupling
diazobenzene chloride with ra-phenylcnediamine. The
free base crystallises in yellow needles, and forms two
series of salts, of which those containing one molecule
of acid are stable. Commercial Chrysoidine is the
hydroehlorido, which forms octahedral crystals, and
dyes wool, silk, and cotton mordanted with tannin,
orange shades.
106 ORGANIC DYESTUFFS
TEIAMIDOAZOBBNZENE,
NH 2 -C 6 H 4 -N =N-C 6 H 3
was first prepared by Martius in 1864 by treating
w-phenylenediamine with nascent nitrous acid, and was
manufactured in England by Dale in 1866. This reaction
yields a mixture of triamidoazobenzene and a much
larger amount of a disazo -compound (Tauber, Her., 1897,
30, 2111, 2899; Mohlau' and Meyer, ibid., 2203) which
forms the commercial product Bismarck brown, Vesuvine,
Phenylene brown, or Manchester brown. It is a basic
dyestuff, which gives brown shades on wool, leather,
and cotton mordanted with tannin, and is still used. It
has since been found (Tauber, Ber., 1900, 33, 2116) that
nitrosophenylenediamine is also obtained on treating
m-phenylenediamine with nitrous acid.
Monoazo Derivatives of Naphthalene.
Constitution. These dyestuffs are formed by the
combination of any diazo-compound with a naphthol, a
naphthylamine, or one of their derivatives. Here again
this combination is governed by rules which are as
follows :
I. In the case of a-naphthol, a-naphthylamine and
their sulphonic acids, coupling takes place in para-(a)
position to the OH or NH 2 groups, providing this position
and the adjacent /^-position are both free. If either of
these positions is occupied, coupling occurs in ortho-(/3)
position to the OH or NH 2 groups. In case this last-
named position is itself also occupied, no coupling will
occur. Examples of this are :
(a) Diazobenzcne chloride combines with a-naphthol
to give benzene azo a-naphthol (I.).
(6) Diazobenzene chloride unites with Neville-
Winther's a-naphthol sulphonic acid to give
the azo-compound (II.)-
AZO-DYESTUFFS 107
N -N C 6 H 5 ' OH
OH
(I-)
(c) Diazobenzene chloride gives with chromotropic
acid the dyestuff
OH OH
S0 3 H
II. In the case of /J-naphthol, /3-iiaphthylamine and
their sulphonic acids, coupling occurs in the a-position
adjacent to the OH or NH 2 group, and never in the
/^-position. If the adjacent a-position is not free,
combination does not occur. Thus /3-naphthylarnine
combined with diazobenzeno chloride gives :
N-N c 6 H 5
It follows that derivatives of a-naphthol and of
a-naphthylamine can give rise to yarn-hydro xy- or ortlio-
amidoazo-com pounds, according to whether the azo-
group is placed in para- or or^o-position to the auxo-
chromes ; the derivatives of /3-naphthylamine and
/ft-naphthol will always be or^o-azo-compounds. The
or^7io-derivatives generally have greater tinctorial pro-
perties.
Hydroxydzo-cowpounds.
The azo-compounds which are formed by the com-
bination of non-sulphonated diazo-compounds with
108
ORGANIC DYESTUFFS
naphthols are insoluble in water. Some have been used
for colouring fats and soaps, and some may be fixed on the
fibre by a special process. In order to obtain soluble dye-
stuffs, it is necessary to introduce into the molecule one
or more sulphonic acid groups. Direct sulphonation
gives mixtures of complex isomers, and it is preferable
to proceed according to one of the following processes :
1. Combination of a diazo -sulphonic acid with a
naphthol.
2. Combination of a diazo -compound with naphthol
sulphonic acids.
3. Combination of a diazo-sulphonic acid with naph-
thol sulphonic acids.
Derivatives of a-naphthol.
DYESTUFF.
AMINE DIAZOTISED.
COUPLED WITH
SHADE ON WOOL.
Tropwolin 3O
or Orange I.
Tropceolin 4O
or Azococcinc.
Azococcine 2R.
Soudan brown.
Azorubine S.
Azoeosine.
Sulphanilic acid.
Aniline.
Xylidine.
a-Naphthylamino.
Naphthionic acid.
o-Anisidine.
a -Naphthol.
N.W. acid.
N.W. acid.
a-Naphthol.
N.W. acid.
N.W. acid.
Orange.
Brick red.
Red.
Red.
Reddish purple.
Certain insoluble azo-derivatives of /i-naphthol have
become of great importance ; they are p-mtrobenzene-
azo-/i-iiaphthol or Paranitr aniline red, and naphthalene-
azo-/3-naphthol or a-Naphthylamine bordeaux. Dyeing
with these insoluble dyestuffs is carried out by first
impregnating (padding) the cotton with a solution of
/?-naphthol in caustic soda, and then, after drying,
immersing the material in a solution of diazo-jp-nitrani-
line or diazonaphthalene, when the dyestuff develops
immediately. In place of /3-naphthol, Naphthol AS.
[Grieshcim Elektron], the anilido of /^oxynaphthoic acid
is now used to produce more brilliant shades of general
fastness.
AZO-DYESTUFFS
109
To obtain soluble products, the monosulphonic
acid, crocein acid, and more frequently the disulphonic
acids R and G are used. It is to be noted that the
same diazo-com pound gives dyestuffs of very different
shades when combined with R acid or G acid, although
these two derivatives only differ in the position of one
sulphonic acid group (seep. 41). Generally, the shades
obtained with R acid are more towards the violet portion
of the spectrum ; whilst G acid yields orange shades
with diazo-eompounds of the benzene series, R acid
gives red shades. (This is the reason that these are
called R and G acids, from the German words Rot
(red) and Gelb (yellow)).
The dyestuffs so obtained are very numerous ; to
this group belong the Ponceaux, Scarlets, etc.
Derivatives of fi-naphthol.
DYESTTJFP.
AMINE DIAZOTISED.
COUrLEI) WITH
SHADE ON WOOL.
Ponceau 4GB
[B.A.S.F.].
Crocein orange,
Aniline.
Schaffer's
Orange.
Brilliant orange.
acid.
Orange G[A.},[M.L.B.]
,,
G acid.
Orange.
[B.A.S.F.].
Ponceau 20 [ A.],
R acid.
Reddisli orange
[M.L.B.], [B.A.S.F.].
Orange No. 3.
w-Ni tramline.
R acid.
Orange.
Ponceau G.
Toluidine.
G acid.
>
Ponceau HT.
R acid.
Orange.
Scarlet GR.
Xylidino.
Schaffer's
Yellowish red.
acid.
Poncrau 2E [A.].
R acid.
Red.
Ponceau G.
G acid.
Orange.
Ponceau Mt[M.L.H.'].
i//-Cumidine.
R acid.
Red.
Bordeaux B [M.L.B.J.
a-Naphthylamino.
tt
Crystal Scarlet [C.J.
a-Naphthylamine.
G acid.
99
Orange II.
Sulphanilic acid.
j3-Naphthol.
Oranee.
Roccelline.
Naphthionic acid.
>>
Red/
Brilliant Ponceau.
?
G acid.
99
Azorubine 2B.
99
R acid.
Crocein 3/?X [By.].
Crocein acid.
>
110 ORGANIC DYESTUFFS
Preparation of Crystal Rcarlet.
S0 3 Na
a-Naphthylamine may be diazotised by suspending
it in dilute hydrochloric acid and adding a solution of
sodium nitrite, but, if it is considered preferable to have
the a-naphthylamine in solution before diazotising,
a-naphthylamine hydrochloride must first be prepared.
For this purpose, 100 grams of the base are dissolved in
400 to 500 grams of warm alcohol, and an excess of con-
centrated hydrochloric acid added ; the hydrochloride is
deposited in silver plates which are separated when
cold. 18 parts of this hydrochloride are dissolved
in 500 parts of water, to which have been added 200
parts of dilute hydrochloric acid (1 : 10), and, when all
of it has dissolved, the solution is cooled to with ice and
diazotised by adding a solution of 7 parts of sodium
nitrite in 50 parts of water. After about ten to fifteen
minutes, the liquid is poured into a solution of 40
parts of G salt dissolved in 700 parts of water, to which
8 parts of caustic soda have been added. The dyestuff
forms slowly, and is precipitated in a crystalline condition.
a-Naphthylamine hydrochloride may also be diazotfced
by suspending in 200 parts of dilute hydrochloric acid
(1 : 10), cooling to 0, and adding 100 parts of a solution
of sodium nitrite (7 grams per litre), when the naphthyl-
amine salt dissolves slowly, the remainder of the process
being carried out as above.
Dihydroxyazo-compounds.
These compounds are obtained by coupling diazo-
compounds with the dihydroxynaphthalenes or their
AZO-DYESTUFFS 111
sulphonic acids. The most important dihyd roxy naphtha-
lenes for this purpose are the 1 : 5 and 2 : 7 isomers ; the
sulphonic acids most frequently used are those in
which the OH groups are in the 1 : 8 or peri-position
(pen'-dihydroxynaphthalene sulphonic acids). Of the
monosulphonic acids, " S acid," and of the disulphonic
acids, chromotropic acid, are the most interesting.
OH OH OH OH
JS0 3 H
SO 3 H
S acid. Chromotropic acid.
S acid is prepared from naphthalene a-sulphonic
acid, which is nitrated and the product reduced, giving
a mixture of 1:5 and 1 : 8 a-naphthylamine sulphonic
acids, which are separated. The 1:8 or " Schollkopf
acid " is sulphonated, when it gives 1-naphthylamine-
4 : 8-disulphonic acid (D.R.P. 40,571). The sodium salt
of this acid is heated at 180 with water in an autoclave ;
or diazotised, and the diazo-compound boiled with
water (D.R.P. 57,388, 74,644). Finally, the a-naph-
thol-4 : 8-disulphonic acid so obtained is fused with
caustic soda (D.R.P. 54,116).
On combining S acid with diazobenzene or diazo-
toluenes, or their sulphonic acids, it gives a series of
dyestuffs called Azomagentas. Chromotropic acid gives
the Chromotropes ; these dyestuffs dye wool, and the
dyed fibre may be developed by chroming. The shade,
which is at first red or violet, becomes an intense black
or bluish black on treating with dichromate.
Amidoazo-compounds.
These are only of secondary importance, the only
interesting one being the red dyestuff called Orchil
112 ORGANIC DYESTUFFS
substitute, prepared by Roussin and Poirrier in 1878
by combining diazo-p-nitraniliiie with naphthionic acid.
Hydroxy -amidoazo-compounds.
The mono-azo-dyestuffs derived from H acid and
Gamma acid do not dye cotton, but some of the mono-
azo-dyestuffs from J acid are direct dyestuffs ; whereas
the azo-compounds from amines of the benzene series
do not possess any affinity for cotton, on coupling with
a-naphthylamine, J acid gives a good direct colour.
The use of N-substituted J acid derivatives containing
an external amido-group, or an amido-group attached
to a heterocyclic nucleus, has led to a large number of
valuable dyestuffs, mostly dyeing orange to red shades,
the amido-group of which can be diazotised and developed
with /3-naphthol for the production of bright red colours.
The Rosanthrene dyestuffs were the first of this series.
The simplest one, Rosanthrene [C.I.B.], is prepared
by combining diazobenzene with the reduction product
of the condensation of ra-nitrobenzoyl chloride with
J acid, and has the following constitution :
SO :} Na ( Y I NH- CO
6 H 5 N = N
OH
Thiazol derivatives of a similar character have been
obtained by condensing J acid with nitrobenzaldehydes,
and boiling the compound obtained with sodium poly-
sulphide, for example :
|N =HO.C 6 H 4 .N0 2
OH OH
Benzylidene compound Thiazol derivative.
AZO-DYESTUFFS 113
On combination with simple diazo-compounds, these
substances give Azo-dyestuffs which form a part of the
Diazo Brilliant scarlet series [By.].
Mordant Monoazo-dyestuffs.
The combination of the diazo-derivatives of amido-
carboxylic acids with amines and phenols, as well
as the combination of diazo-compounds with these
acids, yields monoazo-compounds which dye chrome-
mordanted wool. This property of dyeing on mordants
is possessed to a high degree by dyestuffs derived from
salicylic acid. Alizarin yellow R and GG [M.L.B.]
are produced by the combination of salicylic acid with
p- and ra-nitrodiazobenzene respectively ; the Diamond
yellows are obtained by coupling the diazobenzoic acids
with salicylic acid. Diamond Flavine [By.] has the
following constitution :
HO . C 6 H 4 . C 6 H 4 N = N
and is prepared by tetrazotising benzidine, coupling
with one molecule of salicylic acid, and boiling with water.
The property of dyeing on a mordant may be attributed
to the proximity of the OH group to the carboxyl group ;
it is met with again in the monoazo -derivatives of a-naph-
thol-/?-carboxylic acid and /J-naphthol-a-carboxylic acid.
Chrome-developed Monoazo-dyestuffs. These dyestuffs
are now of great importance for dyeing wool. They
include the hydroxy -monoazo-compounds prepared from
o-amidophenol or naphthol, or their substitution pro-
ducts. These dyestuffs dye wool rather dark shades
from an acid bath, but are converted inlo very rich
tones of fast deep brown, blue, or black, on treating the
dyed fibre with a dilute solution of potassium dichromate,
and heating. These dyestuffs are prepared by diazotising
an ortho- or para-substituted o-amidophenol or o-amido-
O.D.
114 ORGANIC DYESTUFFS
naphthol, and coupling, preferably with /J-naphlhol. In
a similar manner there have been prepared the disazo-
compounds of dihydroxydiamidophenol, which are ob-
tained by a rather unexpected process discovered by the
B.A.S.F. (D.RJP. 138,268, 139,327 ; E.P. 16,811, 20,551
(1901) ). If diamidochlorbenzene sulphonic acid is
diazotised and the tetrazo-compound obtained treated
with an alkali, its chlorine atom is replaced by a hydroxyl
group ; coupling will then take place as usual.
Cl N= N Cl N = N
-N = N Cl A ) N = N Cl
S0 3 H S0 3 H
The following are chrome-developed monoazo-com-
pounds. (From Nietzki, Chemie der org. Farbstoffe, 1906
(5th edition), p. 69) :
Acid Alizarin black R
[M. L.B.I.
Diamond black P.V. [By.].
Anthracene Chrome black [C.]
Palatine Chrome black
[B.A.S.F.].
Nitro-o-amidophfinolsulphonic
acid -f /3 -naphthol.
o-Aniidophenol snlphonic acid
-f- dihydroxynaplithulene.
Amidonaphthol sulphonic acid
R -f /3-naphthol.
o-Amidophenol ^-sulphonic acid
-f /3-naphthol.
The chrome-fixed azo-dyestuffs appear on the mar Let
under numerous names, such as Eriochrome [G.],
Salicin [K.], Erachrome [Lev.], Chromanthrene, [Lev.],
Alizadine [H.], and Mercerol [H.] colours.
Pigment Colours.
The majority of the artificial pigments are insoluble
salts of monoazo-dyestuffs. The value of a pigment
colour depends upon its brilliancy, its fastness to
AZO-DYESTUFFS
H5
light, its covering power, and the insolubility of its
calcium, aluminium, barium, etc., salts. It must also
not be affected by lime, must be quite insoluble in water
and in oil, and must not sublime at too low a temperature.
Very few pigments completely satisfy all these require-
ments, but the number has recently been considerably
extended, although the range of colour is still rather
restricted.
The following are examples of Azo-dyestuffs which are
being manufactured for pigments :
AMINE.
COUPLED WITH
Lithol red R [B.A.S.F.]
2-Naphthyl-
/3-Naphthol.
aminc 1-sul-
phonic acid.
Lake bordeaux B.
do.
-Hydroxy-
naphthoic acid.
Lake red D.
Anthranilic acid.
p-Naphthol.
Pigment orange R [M.L.B.].
p-Nilro-o-tolui-
do.
dine.
Pigment Fast red HL.
}
Helio Fast red RL [By.].
(^ m-Nitro-p-
do.
Lithol Fast scarlet R
{ toluidine.
[B.A.S.F.].
J
Piqinent purple [M.L.B.].
o-Anisidino.
do.
Lake redP [M.L.B.].
p-Nitraniline-o-
do.
sulphonic acid.
Lithol Rubin B [B.A.S.F.].
}p-Toluidine-0-
/3-Hydroxy-
Permanent red 4 B.
sulphonie acid.
naplilhoir acid.
Pigment scarlet 3 B [M.L.B."
Anihranilic acid.
R salt.
DISAZO-DYESTUFFS.
The disazo-compounds contain two azo-groups,
N = N , as chromophores in their molecule. Those
formed by the combination o| two molecules of a diazo-
compound with only one molecule of an amine or phenol
are known as " primary " disazo-compounds. The
characteristic feature of these compounds is that the
two ehromophores are linked to the ring to which the
auxochromes are attached.
116 ORGANIC DYESTUFFS
The " secondary" disazo-compoimds have thechromo-
phores and the auxoehronios attached to different rings.
They may be obtained : (a) by diazotising an amidoazo-
compound and combining with a molecule of an amine
or of a phenol, giving an asymmetrical secondary disazo-
compound ; (b) by tetrazotisirig a diamine and com-
bining with two molecules of an amine or of a phenol,
giving a symmetrical secondary disazo-compound.
Primary Disazo-compounds.
Phenolbisazobenzene .
OH
N = N C 6 H 5
This compound was discovered by Griess in the
products obtained by the action of sodium or barium
carbonates on diazobenzene nitrate. Later Griess ob-
tained it by combining diazobenzene nitrate with benzene
azophenol. It forms yellow plates of M.P. 131.
The diazotoluenes give homologous compounds.
Resorcinol, a-naphthol, and chrysoidine may all
be combined with two molecules of a diazo-compound ;
these two molecules may be identical or different. Thus,
resorcinol combined with one molecule of diazoxylene
and one molecule of diazosulphanilic acid gives Resorcin
brown [A.] :
/ OTT
S0 3 H-C 6 H 4 -N =, N-C 6 H 2 -N = N-C 6 H 3 < p 3
\^ <^"3
OH
The jpm'-dihydroxy- and ^m : amido-naphthol sul-
phonic acids give rise to an enormous number of disazo-
compounds. Thus, chromotropic acid may be combined
AZO-DYE8TUFFS 117
with two molecules of a diazo-compound to give dye-
stuffs of the type :
on OH
N = N X
H acid behaves in a peculiar manner. When coupling
is carried out in alkaline solution, the azo -group enters
the naphthalene nucleus in the /^-position adjacent to
the hydroxyl-group ; whereas, if coupling takes place
in acid solution, the azo-group goes into the /^-position
adjacent to the amido-group. Hence the same diazo-
compound yields different dyestuffs with H acid accord-
ing to whether the combination takes place in acid or
alkaline solution.
NK 2 OH NH 2 OH
X N = "S/ \ N ( \/ \N = N X
S0 3 Hl x A ;S0 3 H
In acid solution. In alkaline solution.
Each of these monoazo-compounds may be combined
with a fresh molecule of a diazo-compound, the first hi
alkaline solution, the second in acid solution. Hence two
isomeric disazo-compounds may be obtained according
to the order in which the groups are introduced :
or
118 ORGANIC DYESTUFFS
The shades of the isomers so obtained differ from one
another.
Amidonaphtliol sulphonic acid G behaves in a similar
manner to H acid ; in acid solution coupling occurs in
ortho-position to the NH 2 , in alkaline solution in ortho-
position to the OH.
on
Naphthol blue-black [C.] is an important dyestuff of
this class. It is obtained by coupling H acid with
diazotised-p-nitraniline in acid solution, and then with n
molecule of diazobenzene in alkaline solution :
OH
N0 2 . C 6 H 4 N = Nf Y|N = N C 6 H 5
'SO 3 H
The ortho-Bulphonic acid of this dyestuff is a black
dyestuff, which is exceedingly fast to light.
The most important compound for the production of
direct dyestuffs is the 2:5: 7-amidonaphthol sulphonic
acid, the so-called J acid. Like H acid it combines with
two diazo-compounds, one in acid and the other in
alkaline solution :
N=N B! (acid)
(alkaline) K 2 N =
OH
Many of the products are, however, too soluble or not
soluble enough to be absorbed by cotton. The Benzo
Fast scarlets [By.], introduced in 1900, are prepared
A20-DYESTUFFS 119
from the urea derivative obtained by the action of
carbonyl chloride on two molecules of J acid, a product
which is capable of combining with two molecules of the
same or different diazo-compounds, and has the con-
stitution :
S0 3 Naf Y | NH C0 NH |
OH OH
The Azidine Fast scarlets [ Jager] are prepared from the
more complex urea obtained by passing phosgene into
one molecule of m-toluylenediamine-4-sulphonic acid and
two molecules of J acid.
Asymmetrical Secondary Disazo-Compounds.
These compounds are obtained by diazotising an
amidoazo-compound and combining as usual with amines
or phenols. The amidoazo -compounds of the benzene
series yield reds, scarlets and bordeaux ; those of the
naphthalene series give very intense browns, blues and
blacks. It is to be noted that, of the amidoazo-com-
pouncls, only those which have the amido-group in the
^para-position can be diazotised ; the amido-group of
o-amidoazo-compounds cannot bo diazotised. All these
dyestuffs are sulphonic acids of type of Biebrich scarlet,
which was discovered by Nietzki in 1879, and was first
manufactured by Kallc & Co. at Biebrich (Nietzki, Ber.,
1880, 13, 1838 ; D.R.P. 18,027). This is produced by
diazotising amidoazobenzene disulphonic acid and com-
bining the product with /3-naphthol :
S0 3 H-C 6 H 4 -N = N-C 6 H 3 -N = N-C 10 H 6 . OH (j8)
SO 3 H
It dyes wool and silk bright scarlet shades.
120
ORGANIC DYESTUFFS
Amidoazobenzone or its sulphonic acids may be
replaced by other amidoazo-compounds, and /3-naphthol
by its sulphonic acids. In this manner an enormous
variety of dyostuffs is obtained.
The azo-blacks are very important substances for the
dyeing of wool ; they are used in place of logwood, which
was previously used exclusively for dyeing wool black.
The first dyestuff of this class was the Blue-black B of
the B.A.S.F. (1883), the next dyestuff prepared being
the Naphthol black of Cassella.
DYESTUFF.
AMINE DIAZOTISED.
COUPLED WITH
RE-DIAKOTISKD
ANJ)
COUPLED WITH
Soudan III. [A.].
Amidoazobonzene.
/3-Naphthol.
Cloth red [By.].
,,
N.W. acid.
Brilliant Crocein fC.].
G acid.
Cloth red B [By.]."
Amidoazo tol uen o.
R acid.
Orchil red A [By.].
Amidoazoxyleno.
Cloth scarlet G [K.].
Amidoazobenzeno
j8-Naphthol.
monosulphonic
acid.
Biebrich scarlet [K.].
Amidoazobenzene
tt
disulplionic acid.
Orcelline [By.].
Amidoazotolueno
N.W. acid.
sulphonic acid.
JVap/< /i f/Zam me 6Zac&
a-Naphthylamine
a-Naphthyl-
a-Naphthyl-
>[C.l.
disulplionic acid.
amine.
amine.
Naphthol black [C.].
/3-Naphthylamine
,,
J{ acid.
disulphonic acid
G.
Je* 6fac& [By.].
Amidobenzene di-
5)
Phonyl-
sulphonic acid.
a-naphthyl-
amine.
Patent Biebrich black
Naphthionic acid.
Oleve's acids.
a-Naphthyl-
4NA [K.].
amine.
Naphthalene Acid
Metanilic acid.
9t
,,
black [By.].
(CH 3 . CO)NH
|
Diaminogen black
so^-AA
a-Naplithyl-
Amido-
[0.].
amine.
naphthol
sulphonio
\A J
acid G.
jjii 2
AS50-DYESTUFF8 121
Symmetrical Secondary Disazo-Compounds.
These compounds are formed by combining two
molecules of an amine or a phenol with the product
obtained by diazotising a molecule of a diarnine. Whereas
a monainine yields a diazo-compound on diazotising,
a diamirie yields a tetrazo -compound.
The first rfisazo-compound known was the one which
occurs with triainidoazobenzeno in Bismarck brown,
formed by coupling tetrazo-m-phenylenediamine with
two molecules of ra-phenylenediamine :
NH
Iii case difficulty is experienced in tetrazotising a
diamine, it may be avoided as follows : a nitro-moiiamine
is diazotised and coupled with an amine or phenol, the
nitro-monoazo-compound treated with an alkali sul-
phide, which only attacks the nitre-group, yielding an
amido-group, and this is then diazotised and coupled
with a further molecule. Another process is to diazotise
the monoacetyl-compound of the amine, couple the diazo-
compound with an amine or a phenol, and treat the
monoacetylamidoazo-derivative so obtained with an
alkali ; the acetyl group is saponified, and coupled
vylth an amine or a phenol. These processes have the
advantage that they can give " mixed " compounds,
that is to say, the two molecules coupled with the
tetrazo-compound are different ; the general formula
for these products is :
X N = N Diamine N = N Y.
Direct Cotton Dyestuffs. Up to 1883, no azo-dyestuff
was known which was capable of dyeing cotton or other
vegetable fibres without mordanting. In this year,
122 ORGANIC DYESTUFFS
Bottigor discovered that on tetrazotising benzidino and
combining with naphthionic acid, a red was obtained
which dyed cotton direct ; it is known as Congo red.
The property of giving substantive or direct cotton
dyestuffs belongs to all azo-derivatives of benzidine and
some of its substitution products such as : tolidine,
obtained from o-nitrotoluene as benzidine is obtained
from nitrobenzene ; dianisidine, derived from o-nitro-
anisol ; diphenetidine, derived from o-nitrophenetol.
Their constitutional formulae are as follows :
NH 9
NTI 2 NH 2
Benzidine. Tolidine. Dianisi- Diphorieti- m-Dichloro-
dine. dine. benzidine.
It is very remarkable that meto-substituted derivatives
of benzidine, such as w-dichlorbeiizidine, etc., yield
disazo-compounds which are not substantive dyestuffs.
NH
Benzidine Diamido- Diamido-
sulphone carbazol. fluorene.
AZO-DYESTUFFS 123
On the oilier hand, all dyestuffs prepared by means
of orJ/ao-substituted derivatives are substantive to
cotton. The substantive character reappears if the
raeta-substituted group is divalent, as in benzidine
sulphone, diamidofluorene, carbazol, etc. The bases are
all ^p-diamines derived from diphenyl. It has been
found that a large number of other ^-diamines, such
as the following, can also yield direct cotton colours :
p-Phenylenediamine (D.R.P. 42,011, 42,814) :
NH 2 C 6 H 4 NH 2 .
Diamidostilbene (Bender, Ber., 1886, 28, 3234;
D.R.P. 39,756) :
NH 2 C 6 H 4 CH = CH C 6 H 4 NH 2 .
Diamidostilbene disulphonic acid (D.R.P. 38,736) :
NH 2 C 6 H 3 CH = CH C 6 H 3 NH 2
S0 3 H S0 3 H.
Diamidodiphenylamine :
NH 2 C 6 H 4 NH C 6 H 4 NH 2 .
Diamidodiphenylurea (D.R.P. 46,737) :
NH 2 C 6 H 4 NH CO NH C 6 H 4 NH 2 .
Diamidodiphenylthiourea :
NH 2 C 6 H 4 NH CS NH C 6 H 4 NH 2 .
All the jp-diamines do not yield substantive dyestuffs,
for example, j9-diamido-diphenylmethane and ^-diamido-
dibcnzyl do not give them. On the other hand, 1 : 5
naphthalene diamine :
124 ORGANIC DYESTUFFS
and its sulplumic acids give direct cotton colours. The
factors which decide the substantive character are not
thoroughly understood even at the present time ; thus
the dyestuffs obtained by combining J acid :
S0 3 1I/ Y ! NH 2
on
or its derivatives with diazo-compounds also have the
property of dyeing cotton directly. The urea derivative
obtained by condensing this acid with phosgene gas, thus
SO 3 H ( V ^iNIIH HHNf V ] SO 3 H
OH OH
is the base of a numerous series of dyestuffs, among
which are Fast Benzo orange S, the Benzo scarlets, etc.
(Mliller, Zeitsch. angew. Chem., 1910, 23, 1489).
Coupling of Tetrazo-compounds. Tetrazobeiizidirie,
and the majority of the other ^-diamines (such as
diamidostilbene), do not immediately combine witli
two molecules of the amine or phenol with which they
are mixed. In alkaline solution or in presence of acetic
acid or sodium acetate, tetrazobenzidine first combines
with one molecule of the amine or phenol ; it is neces-
sary to warm somewhat to obtain combination with
the second molecule. Hence a large number of mixed
disazo-compounds may be prepared of the type :
X N =N C 6 H 4 C 6 H 4 N =N Y.
It is necessary to remember that coupling with ainido-
naphthol sulphonic acids takes place in a different
AZO-DYESTUFFS
125
manner according to whether the reaction occurs in
alkaline or acid solution ; this has been used principally
in the case of symmetrical secondary disazo-compounds.
DYESTUFF.
BASE TETRAZOTISED.
COMBINED WITH
Congo red [A.].
Benzidino .
2 inol. naphthionic acid.
( 1 inol.
Congo Corinth [A.].
( 1 mol. N.W. acid.
Diamine violet N [C.J.
)?
2 mol. amidonaphthol sul-
phonic acid G (in acid
solution).
1 1 mol. amidonaphthol sul-
Diamine brown V [C.].
1 phonic acid G (in alka-
line solution)-!- 1 niol.
\ m-phenylenediarnine.
C 1 mol. G acid.
Diamine scarlet [C.].
fj
J 1 mol. phenol, and then
( ethylatod.
Benzo orange R [By.].
,>
( 1 mol. salicylic acid.
\ 1 mol. naphthionic acid.
Diamine black RO [C.].
3-
2 mol. amidonaphthol sul-
phonic acid G (in alka-
line solution).
DiamineblackBH [C.].
(1 mol. 7-acid.
1 mol. H acid.
Diamine blue 2B [C.].
f>
2 mol. H acid (in alkaline
solution).
^1 mol. salicylic acid.
Diamine brown [M.L.B.]
f>
I 1 mol. amidonaphthol sul-
1 phonic acid G.
Benzopurpurine 4B
Tolidine.
^2 mol. naphthionic acid.
[By.], [Lev.].
Diamine blue W [C.].
^
2 mol. H acid.
( 1 mol. H acid (in alkaline
Diamine blue BX [C.].
%)
\ solution).
U mol. N.W. acid.
Dianil blue Q.
Dianisidino.
2 mol. chromotropic acid.
Diamine black 30 [C.].
Ethoxybenzi-
2 mol. amidonaphthol sul-
dine.
phonic acid G (in alka-
line solution).
Benzopurpurine IOB.
Dianisidine
2 mol. naphthionic acid.
[By.], [Lev.].
Diamine sky blue.
99
2 mol. II acid.
Pyramine orange [By.].
Benzidino
2 mol. nitro-m-phenylono
disulphonic
diamino.
acid.
126 ORGANIC DYESTUFFS
TRISAZO-DYESTUFFS.
These compounds contain three N = N groups in
the molecule. They are generally very intense dyestufl's
of blue, dark green, or black shades, and may be
obtained by several processes :
(1) A symmetrical secondary disazo-compound is pre-
pared containing an NH 2 group which can be diazotised,
that is not in or^o-posit ion to the N = N chromo-
phore ; this is diazotised and the diazo-disazo-compound
so obtained coupled with a suitable compound. For
example :
Diamine bronze G [C.]. Tetrazobenzidine is combined
with one molecule of salicylic acid, and one molecule of
amidonaphthol disulphonic acid H in alkaline solution,
the product diazotised and coupled with /w-phenylene-
diamine, giving :
coon
C 6 H 4 N = N
[ SO 3 H
A large number of these dyestuffs are obtained by
replacing the benzidino by other diamines, and H acid
by a-naphthylamine or Clevc's acids.
(2) A mixed symmetrical secondary disazo-compound
is prepared by combining a tctrazodiamine with a suit-
able compound in one part of the molecule, and also, in
another part, with a phenol or an amine which can bo
coupled with another diazo -com pound. For example :
Diamine green [C.]. Tetrazobenzidine is coupled with
one molecule of salicylic acid and one molecule of H acid
in alkaline solution. When the reaction is complete,
the dyestuff produced is combined with a nioloculo of
diazo-p-nitraniline in acid solution, giving :
AZO-DYESTUFFS 127
It has already been mentioned that, if difficulties are
experienced in the preparation of the necessary tetrazo-
diaminc, an indirect method is used, which consists of
diazotising the monoacetyl-derivative of the ^-diamine,
coupling with an amine, diazotising, and again coupling,
and finally saponifying the acetyl group. The amido-
disazo-compound obtained is then diazotised and suitably
coupled. This method yields the Diaminogens. The
acetylnaphthalenediamine sulphonic acids are diazotised,
aii( 1 coupled with a-naphthylamine ; the dyestuff produced
is diazotised, and combined with a naphthol sulphonic
acid or an amidonaphthol disulphonic acid. With R
acid, tho following disazo-compound is obtained :
OH SO 3 H
. NH< >N = N< >N = N<
SO 3 H SO 8 H
Elimination of the acetyl group gives Diaminogen
blue [C.], which may be diazotised, and again coupled.
Dyestuffs of the Diaminogen class which contain a
p-diamine are direct cotton colours, and these may be
diazotised on tho fibre and combined with phenols or
naphthols, giving trisazo-dyestuffs. As a trisazo-com-
pound still contains an NH 2 group which can be
diazotised, it will yield a tctrakisazo-compound on
diazotising and coupling. This last coupling process is
often effected on the fibre.
128
ORGANIC DYESTUFFS
The following table gives some of the more important,
trisazo-dyestuffs :
DYESTUFF.
Bcnzo olive [By.].
Benzo blue-black R [By.]
Diamine green B [C.].
Azocorinth [O.].
COMPOSITION.
T) -j- ^salicylic acid.
Benzldlne <a-naphthyIamino-Hacid.
, acid.
rp i-i- .xl 1 * . VV , ilClU.
loiiame <. a . naph thylainine N.W. acid.
1 . 1
salicylic acid.
rp j.j. ^resorcinol naplithionic acid.
^amidohenol sulhonic acid.
amidophenol sulphonic acid.
CHAPTER XIII.
HYDRAZONES.
THKSK compounds are produced by the action of
hydrazine or substituted hydrazines on aldehydes and
kot ones. The most important are the phcnylhydrazoncs
obtained by using phenylhydrazine and its nitro- and
sulphonated derivatives ; these are. coloured substances,
certain of which are true dyestuffs. There is a very close
relationship between the phenylhydra zones and the azo-
dvestuffs ; thus benzene azo-u-naphthol (I.), is identical
with the phenylhydrazone of a-naphthaquinone (II.),
obtained by treating this quinone with pheiiylhydrazine.
= o
(II.)
The identity of these two substances shows that in
one case the reaction has been accompanied by a mole-
cular change, either from left to right in the above
formulae, or vice versa. At first it was thought that
the azo-compounds had a quinonoid constitution. The
differences which had been proved to exist between the
o-hydroxy- and o-amidoazo-compouiids and 'their para-
isomers, had caused the or/*o-derivatives to be classed with
O.D. i
130 ORGANIC DYESTUFFS
the hydrazones, whilst the ^-hydfoxy- and y)-amidoazo-
dyestuffs were considered to be true azo-compounds
(Goldschmidt and Low-Beer, Ber., 1905, 38, 1098).
However, the researches of Goldschmidt and Low-Beer,
MacPherson, Willstiitter and Veraguth, and R. Auwers,
to mention only the most recent publications, have shown
that the ortho- and 2?ara-hydroxyazo-compounds have
a similar constitution, and in all probability are not
quinonoid.
The hydrazones used as dyestuffs generally have a
cyclic formula :
Isatin yellow is the sodium salt of the jp-sulphonated
phenylhydrazone of isatin.
Phenanthrene red is the sodium salt of ^-sulphonated
diphenylhydrazone of phenaiithraquinone.
Tartrazine.
This compound is the most interesting member of the
Hydrazones. It was first prepared in 1884 by Ziegler and
Locher (Ber., 1887, 20, 834 ; D.R.P. 34,294) by treating
dioxytartaric acid with phenylhydrazine _p-S!il phonic
acid. At first this dyes tuff was considered to be a
diphenylhydrazone, but the researches of Anschutz (Ann.,
1896, 294, 219), and of Gnehm and Benda, have shown it
to be a pyrazolone. It is prepared by heating phenyl-
hydrazine sulphoiiic acid with sodium dioxyt art rale
and a small amount of water.
HOOC CO CO
+ 2NH 2 NH C 6 H 4 3 H
HOOC C C =N NH C 6 H 4 SO,H
+ 3H 2
ii T
N CO
N
C 6 H 4 -S0 3 H
Tartrazine may also be obtained by commencing with
HYDRAZONES 131
oxalacetic ether, and treating with phenylhydrazine
sulj>honic acid to give a pyrazolono, which is then treated
with diazosulphanilic acid, and the ethyl ester produced
saponified :
C 2 H 5 OOC C CH 2 N=N C 6 H 4 SO,
N CO +
\/
N
C H 4 SO 3 Na
H OOC CC = N X H C 6 H.,S( ) 3 T I
N CO
\/
-> N
i 6 H 4 S0 3 H
The azo-compound obtained apparently gives the
isomcric hydra zone.
Commercial Tartrazine is the sodium salt, an orange
yellow powder which (lyes wool a brilliant greenish
yellow shade, which is extremely fast to light.
If the phenylhydrazine sulphonic acid is replaced by
other derivatives and the oxalacetic ester by similar
compounds, other dyestuffs of this group are obtained,
such as the Ffavazines [M.L.B.], the Hydrazhie yellows
[Grieslieim], and the Light Fast yellows [By.]. They
dye wool and silk, and are also used in the manufacture
of pigment colours.
The Xylcne yellows (Sandoz, E.P. 3373 (1908)) are
dichlor-sulphonic acids of l-phenyl-3-methyl-5-pyrazo-
lonc: PW IL\
L/xl 2 (4)
(3) CH 3 .C ./NcO(5)
N-N-C tf H 8 (i)
(2)
132 ORGANIC DYESTUFFS
which is obtained by condensing phenylhydrazine with
ethyl acetoacetate. Radial yellows [B.A.S.K.] are closely
allied dyestuffs.
Eriochrome red B [G.] contains the or^o-hydroxy-
azo-group essential for a chrome colour, and is produced
by the combination of diazotised l-amido-2-naphthol-
4-sulphonic acid with the above phenylmethylpyrazo-
lone : Oil X N v
CH 3 . C CO HO,
N N . C H,
SO.",NJI
It gives dull red shades on wool, which change to bluish-
red on after-chroming.
CHAPTER XIV.
STILBENE DYESTDFFS.
STILBENE or diphenylethyleno, C 6 H 5 ( 1 H=CH C H 5 ,
is the parent substance of a number of dyes tuffs which
have been known for a considerable time. In 1883
Walter (Bull. Soc. ind. Mulliouse, 1887, 99) obtained
an orange dyestuff by heating 2> -nit-rot oluene sulphonic
acid with caustic soda. Bender showed that this
product is derived from stilbene, as on reduction it
gives diamidostrilbene disulphonic acid :
SO 3 H /S0 3 H
;C 6 H g -CH = CH-C g H 8 <;
NH/ X NH 2 .
According to the conditions under which the p-nitro-
toluene sulphonic acid is treated with caustic soda the
products are different. Dilute boiling caustic soda
gives Sun yellow or Heliochrysin (G. Schultz and Bender.
J3er., 1886, 19, 3234), whereas concentrated caustic
soda at 80 gives Direct yellow G. [K.] (O. Fischer and
Hepp, Ber., 1893, 28, 2233 ; 1895, 28, 2281). All these
products dye cotton directly an orange shade ; by the
action of oxidising agents, greener shades are produced,
such as Mikada golden ijellmv ; whereas on reduction
the shade becomes redder, Mikado orange [L.], etc.
(D.R.P. 46,252, 48,528). According to Fischer and Hepp,
f^un yellow should be azoxystilbene disulphonic acid, and
the Direct yellow dinitrosostilbene disulphonic acid.
They result from the condensation of two molecules of
#-nitrotolrone sulphonic acid by intramolecular oxidation:
134
ORGANIC DYESTUFFS
CH- CHo
CH = CH
SO 3 H SO 3 H
SO 3 H
4- 2H,,0
NO
NO
NO
Oxidation should convert this derivative into dinitro-
stilbene disiilphonic acid, and this should be Mikado
yellow. This constitution is, however, incorrect, as the
true dinitrostilbene disiilphonic acid has been prepared
by Green and Wahl (Ber., 1897, 30, 3101 ; 1898, 31,
1078) by oxidising jj-nitrotolueiie sul])honic acid with
sodium hypochlorite ; it is a pale yellow substance which
does not dye cotton. In addition to dinitrostilbene
disiilphonic acid, oxidation in alkaline solution gives
more or less dinitrodibenzyldisulphonic acid, according
to the conditions, and both these oxidation products give
dyestuffs with alkaline reducing agents. These dycstufTs
appear to be identical with the Mikado colours, and are
called Stilbcne yelloiv and Stilbene orange. The con-
stitution of these products has been established by
Green and his co-workers (Green, Marsden and Schofield,
J.C.8., 1904, 85, 1424, 1432 ; Green, Davies and Horsfall,
ibid.. 1907, 91, 2070 ; Green and Baddiley, ibid., 1908,
93, 1721) by the study of the various aldehydes formed
by oxidising with permanganate. Stilbene yellow 80
contains two st ilbene residues linked by an azo-group :
CH=OH
S0 8 H C 6 H 3 C 6 H 3 S0 3 TI
4H 2
NO 2 N
NO, N
S0 8 ir (J fl
CH = CII
SO.JI
STILBENE DYESTUFFS 135
Direct yellow RT, Afghan yellow, and Sun yellow are
considered to have the constitution :
CH . C,.H H (SO,H) . N==N . C G H 3 (S0 3 H) . CH
H . C 6 H 3 (S0 3 H) . N N . C,H 3 (SO 3 H) . CH
Curcumin S is identical with Sun yellow, and is not
to be confounded with true Curcumin, the colouring
matter of turmeric, which, according to Mitobedzka,
Kostanecki and Lampe (Ber., 1910, 43, 2163) probably
has the formula :
OCH
X CO.CII:CH<; ;OH
/
Clio
>co . cii :
OCH 3
which would explain, by the symmetrical position of the
two chromophores, the property of Curcumin of dyeing
unmordanted cotton.
When p-nitrotoluene sulphonic acid is treated with
caustic soda in presence of amido-compounds, such
as j)-amidophenol, p-phenylenediamine, benzidine,
dehydrothiotoluidino, etc., new dyestulTs are obtained
which are named respectively: Polychromin Arnica
yellow, Chicago orange, Curcuplienin, etc.
Preparation of Direct Yellow.
p-Nitrololucne Sulphonic acid.
2 kilograms of fuming sulphuric acid containing
30 per cent, of SO 3 are heated to 00-05, and 500 grams
of p-nitrotolueno added slowly with constant stirring,
136 ORGANIC DYESTUFFS
the heating being continued until a drop of the liquid
dissolves completely in water, and the smell of the
original nitro-compound has disappeared. The mass is
then poured slowly into 8 or 10 litres of cold water, and
common salt added until the sodium salt of the smlphonic
acid is precipitated. After cooling, the salt is separated,
and dried. In order to obtain the pure sodium salt,
it is necessary to recrystallise from water, but for con-
version into the dyestuff this is unnecessary. The
amount of pure salt in the product must be known, and
this is determined by igniting a known weight of the
product with concentrated sulphuric acid, and weighing
the sodium sulphate formed.
"Direct yellow. Five parts of caustic soda solution
(27 Tw.) are heated to 80, and one part of the above
sodium sulphonate added ; the mass thickens and
becomes an orange brown colour, and after some time
is poured into twenty times its weight of water, allowed
to settle, and filtered.
CHAPTER XV.
DIPHENYLMETHANE DYESTUFFS.
A CONSIDERABLE number of dyestuffs are more or less
directly related to diphenylmethane :
C 6 H 5 CH 2 C G H 5 .
On oxidation this hydrocarbon gives a ketone, benzo-
phenone : C 6 H 5 CO C 6 H 5
and this on reduction first yields a secondary alcohol,
diphenylcarbinol or benzhydrol, which, on further
reduction, gives diphenylmethane :
C 6 H 6 CHOH C 6 H 5
CJI 6 niOH 6 H 5
These compounds are colourless, the dyestuffs being
obtained from their amido- or alkylamiclo-derivativcs,
which can undergo the above series of reactions. The
only amido-derivatives of interest are those in which
the amido- or alky lam ido-groups are in para-position,
as, for example, tetramethyldiamidocttphenyhiiethane,
tetramethyldiamidobenzophenono, tetrainethyldiamid*-
diphenylcarbinol.
138 ORGANIC DYESTUFFS
Tetramethyldiamidodiphenylmethane y
(CH 3 ) 2 N-C 6 H 4 -CH 2 -C 6 H 4 -N(CH 3 ) 2 ,
is prepared by a very simple reaction, a solution of
dimethylaniline in dilute hydrochloric acid being treated
with formaldehyde, when one molecule of aldehyde
condenses with two molecules of the tertiary amine,
combination taking place in ^para-position :
CH 2 O 4- ^ = H 2 O + CH 2
The product is purified by recrystallisatioii from
alcohol, and forms plates of M.P. 90-91.
Tetramethyldiamidobenzophenone, " ketone base,"
(CH 3 ) 2 N-C 6 H 4 -CO-C 6 H 4 -N(CH 3 ) 2 ,
was prepared in 1876 by treating dimethylaniline with
carbonyl chloride (W. Michler, Ber., 1876, 9, 715;
Michler and Dupertuis, ibid., 1900), and is still known
as " Michler's ketone." The process is used at the
present time, the gas being absorbed in dimethylaniline
until the increase in weight corresponds to one molecule
of carbonyl chloride for two molecules of dimethyl-
aniline ; the product is then heated in an autoclave,
poured into water, and the excess of dimethylaniline
separated by steam distillation.
COC1 2 + 2C 6 H 6 N(CH 3 ) 2 = 2HC1
Condensation only takes place in ^para-position to the
nitrogen ; there are also formed as secondary products
dimethylamidobenzoic acid and hexamethyltriamidodi-
benzoylbenzene :
(CH 3 ) 2 N-C 6 H 4 -CO-C 8 H3-CO-C G H 4 -N(CH 3 ) 2
N(CH 8 ),
DIPHENYLMETHANE DYESTUFFS 139
Michler's ketone crystallises in greyish plates of M.P.
179. It is soluble in acids to a yellow solution, and
gives light yellow shades on wool, silk, and cotton mor-
danted with tannin.
Tetramethyldiamidobenzhydrol.
(CH 3 ) 2 N C 6 H 4 CHOH C 6 H 4 N(CH 3 ) 2
This is often called " Michler's hydrol." It may be
obtained by the oxidation of tetramethyldiamidodi-
phenylmethane, or by the reduction of Michler's ketone
in alkaline solution. The first process has the advantage
of avoiding the preparation of Michler's ketone, and hence
the use of the poisonous carbonyl chloride. The oxida-
tion of tetramethyldiamidodiphenylmethane is carried
out in acetic acid solution by the theoretical amount of
lead dioxide (D.R.P. 79,250). Michler's ketone is readily
reduced by sodium amalgam in boiling alcoholic solution
(Michler and Dupertuis, loc. cit.), by zinc powder and
caustic soda in boiling amyl alcohol solution (B.A.S.F.,
D.R.P. 27,032) ; more recently calcium and alcohol have
been suggested (Marschalk and Nicolajewski, Ber., 1910,
43, 641, 1701).
IMichler's hydrol dissolves readily in alcohol and
ether, and forms prisms of M.P. 96 ; on heating in
alcoholic solution, it is dehydrated. It dissolves in
acids to give a magnificent bluish purple colour, which
is unstable, and dyes wool and silk fugitive blue shades.
Auramine, C 17 H 21 N 3 .
This is the only important diphenylmethane dycstuff.
It was discovered by Kern and Caro in 1883 by fusing
Michler's ketone with ammonium chloride and zinc
chloride (B.A.S.F., E.P. 29,060, 31,936, 38,433 (1886)).
C 6 H 4 -N(CH 3 ) 2 C 6 H 4 N(CH 3 ) 2
CO + NH, C = NH + H 2 O
! 6 H 4 -N(CH 3 ) 2 C 6 H 4 -N(CH 3 ) 2
140 ORGANIC DYESTUFFS
In order to avoid the use of carbonyl chloride, Walter
in 1887 (Butt. Soc. ind. Mulhouse, 1895, 82) and Sand-
meyer in 1893 (Geigy, D.B.P. 53,614, 58,277) pre-
pared Auramine by passing a current of ammonia into
a fused mixture of dimethyldiamidodiphenylmethane
and sulphur, when the thioketone formed reacts with
the ammonia. Auramine is also prepared by treating
the product obtained by the action of phosphorus
oxychloride on ^-dimethylbenzoylmethylaniline with
dimethylaniline (Hochst Farbwerke, D.R.P. 41,751,
44,077).
The free base of Auramine is colourless, but its salts
are coloured, and are easily crystallised ; the commercial
product is the hydrochloride. It is a basic dyestuff,
dyeing wool, silk and tannin-mordanted cotton a yellow
shade ; it is also used for colouring paper. It is reduced
with difficulty to leuco- Auramine, C J7 H 23 N 3 .
A series of Aur amines is obtained from the homologues
of Michler's ketone or the amidotolylmethane ; for
example, Auramine G is obtained by using dimethyl-
clitolylmethane, sulphur, and ammonia (B.A.S.F., D.R.P.
67,478).
The constitution of the Auramines has been the subject
of a number of researches (Graebe, Ber., 1887, 20, 3260 ;
Fehrmann, ibid., 2844 ; Stock, Journ. f. prakt. Chem.,
1893, 47, 401 ; Semper, Ann:, 381, 244) ; at the present
time one or other of the following formulae is considered
to express the constitution of ordinary Auramine :
C - <^ ^> = N(CH 8 ) 2
I I
NH 2 Cl
Stock's formula.
Nil . IIC1
Graobe's formula.
DIPHENYLMETHANE DYESTUFFS 141
If Graebe's formula is correct, Auramine is the hydro-
chloride of tetramethyldiamidodiphenylimine. This
formula appears to be correct by the readiness with
which the dyestuff is hydrolysed on standing in aqueous
solution, and more rapidly on boiling or by dilute acids,
into ketone base and an ammonium salt. There are,
however, certain reasons for which certain authors have
considered it necessary to attribute to Auramine a
quinonoid structure (see Nietzki, Chemie der organ.
Farbstoffe, 5th edition, p. 131). There is perhaps still
another method of representing the constitution of
Auramine ; it has been stated that Michler's ketone is
a weak dyestuff which becomes an intense yellow on
addition of acids. It is, hence, probable that, in the case
of the hydrochloride, this salt has the constitution (I.),
and by analogy (II.) should represent the constitution
of the corresponding imine, that is, of Auramine :
(CH 3 ) 2 N-C 6 H 4 -CO-C 6 H 4 -N(CII 3 ) 2
(I.) 01 H
(CH 3 ) 2 N-C 6 H 4 -C-C e H 4 -N(CH 3 ) 2
(11.) NH Cl H
CHAPTER XVI.
TRIPHENYLMETHANE DYESTUFFS.
TRTPHENYLMETHANE and its higher homologues, di-
phenyltolylniethane, phenylditolylmethane, etc., are
colourless, crystalline hydrocarbons which yield a large
number of dyestuffs. These are derived from the pro-
ducts obtained by oxidising the hydrocarbons, which
were called carbinols by Kolbe. Triphenyhn ethane (I.)
yields triphenylcarbinol (!!.)> that is, methyl alcohol
(carbinol) in which the three hydrogen atoms of the
methyl group have been replaced by phenyl groups :
C 6 H 6 C C II 5
H C C 6 H 5 HO C C 6 H 5
\ (I.) \ (ID
C 6 H 5 C C H 6
Like the hydrocarbons, the carbinols are colourless
substances, and in order to obtain dyestuffs it is necessary
to introduce auxochromes into the carbinol molecule
in para-position to the carbon atom of the methane
residue. Hence there are two groups of these dyestuffs :
(1) The amido- or alkylamido-derivatives, in which
the auxochromes are NH 2 and NR 2 groups ;
(2) The hydroxy-derivatives, in which the auxo-
chromes are OH groups.
The amido -derivatives include : Malachite green,
the Magenta series, and their substitution products.
The hydroxy-derivatives include the Aurines.
Finally, there are the dyestuffs derived from phthalic
acid, the Phthaleins and RJwdamines, which are also
derived from triphenylmethane.
TRIPHENYLMETHANE DYESTUFFS 143
AMIDO-DERIVATIVES OF TRIPHENYLMETHANE.
If an amido-group is introduced into the triphenyl-
carbinol molecule in #ara-position to the carbon atom
of the methane residue, ^-amidotriphenylcarbinol is
obtained :
OH
This compound is colourless, but with mineral acids,
gives salts of an orange red colour which have a very
feeble tinctorial power. These coloured salts are formed
by the action of a molecule of the base on a molecule
of acid, with elimination of a molecule of Avater. This
reaction may be regarded in two ways, the simplest
being represented by the following equation :
nH 5 > C C 6 H 4 NH 2 + HC1
^6 X1 5 I
OH
6 H 4 NH 2 + H 2
1
01
1
in which it will be seen that the hydroxyl group of the
carbinol has been replaced by an atom of chlorine. This
explanation was proposed by Roseiistiehl for all the
coloured salts derived from tripheiiylmethane, but has
been opposed and is now practically abandoned in spite
of its apparent simplicity, on the grounds that the
formulae of the hydrochlorido, the carbinol and the
hydrocarbon would be very similar :
P G U 5 > C C 6 H 4 NH 2 6 2 5 > C C 6 H 4 -NH 2
^-"S I ^B^S I
H OH
Colourless hydrocarbon. Colourless carbinol.
Cl
l
Coloured hydrochloric! (Rosenstiehl).
144 ORGANIC DYESTUFFS
Thus, the colour of the hydrochloride would appear
to be dependent merely on the replacement of hydrogen
by chlorine, whereas if one or more hydrogen atoms of
a hydrocarbon are replaced by chlorine, the derivative
obtained is generally still colourless. Thus, benzene and
toluene give colourless chlorine derivatives ; methane
is a colourless gas, and its mono-, di-, and tri-chloro-
derivatives are colourless. Hence Rosenstiehl's formula
appears to be insufficient.
Triphenylcarbinol and triphenylchloromethane, ob-
tained by tke action of dry hydrochloric acid on
triphenylcarrbinol ,
CftMir^,
65 | = H 2 + CH 5>C ~ C H *
iOH HJC1 6 5 I
Ol
are both colourless substances, and the colour only
appears when there is an amido-group in the molecules
in the para-position. It would, therefore, appear that,
as the amido-group is necessary for the formation of a
coloured salt, it should take part in the reaction. It may
be considered that the acid first combines with the
basic amido-group to give a normal salt which then loses
a molecule of water :
/"I TT **^
The coloured salt should then bo the hydrochloride
of a base C 10 H 15 N, differing in formula from carbinol
by one molecule of water, but the base has not yet been
TRIPHENYLMETHANE DYESTUFFS 145
isolated. This base has been called fuchsonimine by
Baeyer and Villiger (Ber., 1904, 37, 597, 2848). This
formulation (p. 144) was proposed by Fischer for all
the amido-triphenylmethane dyestuffs, and has the
advantage that these dyestuffs are considered to be
derivatives of quinone. Since the researches of Fischer,
the view held with regard to the constitution of quinone
itself has been modified, and at present the formula B is
accepted in place of the older formula A.
o
CH
CH
(A.)
CII
CH
CH
CH
(B.)
CH
CH
O
Nietzki has modified the constitutional formulae
used to represent the triphenylmethane dyestuffs in a
similar manner, and at the present time fuchsonimine is
considered to be represented by (II.) in place of the older
formula (I.), and its hydrochloride is called fuchsoni-
monium chloride (III.).
CII K
NH
H N H
(I.) (II.) . ci (III.)
This quuionoid notation represents the carbinols and
their salts by entirely different formulae. It appears
natural that, with the conversion of the colourless
O.D, K
146 ORGANIC DYESTUFFS
carbinol into a coloured salt, a very groat change
should occur in the linking of certain of the atoms and
their relative positions in the molecule. This modi-
fication of the linkages is represented by the new
formulae, which have the further advantage of bringing
this group of dyestuffs into agreement with the quinonoid
theory. (See Wahl, Revue gdnfrale des Sciences, 1905,
p. 558 : " Les iclees actuelles sur la constitution des
colorants du triphenylmethane.")
Diamido-derivatives of Triphenylmethane.
Fuchsonimonium chloride is a very feeble dyestuff,
but it is a chromogen, as, on introducing a further amido-
group in 2?ara-position to the carbon atom of the methane
residue, there is produced Dobner's violet, or amido-
fuchsonimonium chloride :
H Cl
This is the simplest diamido-derivative of triphenyl-
methane, and was discovered by Dobiior in 1878 by
heating benzotrichloride with aniline and nitrobenzene
(Ber., 1882, 15, 234). It is no longer of any importance,
but its tetramethyl derivative, MalacJnte green, is of
very great interest.
Malachite green.
This dyestuff was first prepared by O. Fischer in 1877
by heating benzaldehyde with dimethylanilirie and zinc
chloride, and oxidising the product obtained (E. and O.
Fischer, Ber., 1877, 10, 1625 ; 1878, 11, 950 ; 1879, 12,
791, 796, 2348). In 1878 Dobner obtained the same
dyestuff by heating benzotrichloride with dimcthylaniline
and zinc chloride (Ber., 1878, 11, 1236, 2274 ; D.R.P.
4322, 4988, 18,959). This last process has been replaced
by the benzaldehyde process, which has itself been
slightly modified.
TRIPHENYLMETHANE DYESTUFFS 151
(CH 3 ) 2 N C 6 H 4 C = C 6 H 4 = N<^"
HO 1
CH
Patent blue is an acid dyostuff which dyes wool and
silk from an acid bath, giving greenish blue shades which
are fast to soap and alkalies. Cyanol, or Acid blue 6 G,
is obtained by using monoethyl-o-toluidine, and Patent
blue A from ethylbenzylaniline.
At first, the fastness to alkalies and the change of
shade was considered to be due to the presence of the
hydroxy-group in the raeto-position. In the years 1896-7,
Suais in France and Sandmeyer in Switzerland showed
independently, by different methods, that the fastness
to alkalies is really due to the presence of a sulphonic
acid group in orJAo-positioii to the carbon atom of the
methane residue (Sandmeyer, J. Soc. Dyers and Col.,
1896, 154). Suais condensed tetramethyldiamidobenz-
hydrol with metanilie acid, when combination occurs
in ^para-position to the amido-group, giving (I.) :
(CH 3 ) 2 N - C 6 H 4 CH C 6 H 4 N(CH 3 ) 2
I S0 3 H
(II.)
152 ORGANIC DYESTUFFS
Compound (I.) is diazotised, boiled with alcohol to
eliminate the amido-group, and then oxidised to give
the dyestuff (II.), which is the o-sulphonic acid of
Malachite green. This dyestuff differs in shade from
Malachite green, being more bluish, and in its great
fastness towards alkalies.
Sandmeyer condensed benzaldehyde o-sulphonic acid
(obtained by heating o-chlorbcnzaklehyde with sodium
sulphite under pressure) with dimethylaniline, and after
oxidation obtained the dyestuff (II.)- This process was
patented by the firm of Geigy (Basle), and is used in
the preparation of Erioglaucine by condensing benz-
aldehyde o-sulphoiiic acid with ethylbenzylaniline or
its sulphonic acids. This dyestuff has the formula :
SO 3 H.C H 4 .(C 2 H 5 )N C C H 4 C =C 6 H 4 = N(CoH & ).C H. t .SO 3 n
-SO 2
More recent researches have shown that the sulphonic
group in the ortho-position may be replaced by other
acid or negative groups, such as Cl, Br, N0 2 , CN,
COOCH 3 , etc. The dyestuffs Eriochlorine, Setoglaiicine,
Setocyanine and Eriocyanine [Geigy], apparently belong
to this series.
Amongst the other substituted derivatives of Malachite
green may be mentioned Glacier blue (D.R.P. 71,370
(1892) ) and Victoria green 3B (D.R.P. 25,827), which are
derivatives of dichlorobenzaldehyde.
The influence of substitution in the Malachite green
scries has been studied systematically by Nolting and
Gerlinger (Ber., 1906, 39, 2041).
Attempts to condense tetramethyldiamidobenzhydrol
with naphthalene disulphonic acid have been successful,
giving the Naphthalene greens [M.L. B.] which are fast
to alkali.
TPJPHENYLMETHANE DYESTUFFS 153
Triamido-derivatives of Triphenylmethane.
Historical. To this class belongs Magenta, the
first synthetic dyestuff known, the study of whose
properties and chemical composition has largely contri-
buted to the rapid development of the aniline colour
industry.
In 1856 Nathanson noticed that on heating crude
aniline with ethylene chloride at 200 C., a red dyestuff
was formed ; in 1858 Hoffmann also obtained a red
dyestuff by treating aniline with carbon tetrachloride.
It was, however, the French chemist, Verguin, of Lyons,
who, in 1859, discovered the process, employed com-
mercially for> some time, of heating commercial aniline
with stannous chloride. This discovery was patented on
8th April, 1859, by Renard Bros. & Franc, of Lyons,
and the dyestuff was sold under the name of iw Fuchsi-
asine " or " Fuchsine." Shortly afterwards the manu
facture of this substance became the property of the
Fuchsine Company with a capital of four million francs.
At first the profits made were enormous ; about the year
1860, Magenta (Fuchsine) was sold at 1,500 francs per
kilogram, an amount which is at present worth five to six
francs. About the same time Durand and Gerber-Keller
obtained a red dyestuff called Azalem by heating aniline
with mercury nitrate ; their French patent was annulled
and their works taken into Switzerland. The Verguin
process gave a very small yield (only 15-5 per cent.).
In January, 1860, the use of syrupy arsenic acid for oxi-
dising was patented about the same time by Medlock (E.P.
18th Jan., 1860) and Nicholson (E.P. 26th Jan., 1860) in
England, and by Girard and de Laire (B.F. 26th Jan.,
1860) in France. This arsenic acid process was gradually
abandoned because the Magenta so obtained frequently
contained arsenic acid, which rendered it poisonous. It
was replaced by the nitrobenzene process discovered by
Coupier in his works at Creil, where pure nitrobenzene
and nitrotoluene were manufactured. He noticed that
154 ORGANIC DYESTUFFS
by heating a mixture of toluidine and nitrotoluene with
iron and hydrochloric acid, there was produced a red
dyes tuff similar to or identical with Magenta. When the
Fuchsine Company instituted proceedings against
Coupler, Rosenstiehl succeeded in showing that Coupler's
pure toluidine contained two isomors, ortho- and para-
toluidine, and that the red obtained was different from
Verguin's Magenta. Coupler's nitrobenzene process is
the one generally used at the present time ; homologues
of Magenta are, however, obtained by the synthetic
formaldehyde process.
Constitution of Magenta.
The detailed study of the Magenta obtained by oxidis-
ing commercial aniline, containing toluidines, was under-
taken by Hofmann in 1862, and it was found by him to
consist of the hydrochlorido of a base C 20 H 19 N 3 H 2
which he called rosaniline. Pure aniline did not
yield this red dyestuff on oxidation, and, in order to
obtain the dyestuff, it was necessary to mix it with
toluidine. The only toluidine known at that time was
the solid ^pam-toluidine, but, like pure aniline, this by
itself did not give a red dyestuff on oxidation. Hofmann
concluded that Magenta is formed by the oxidation of a
mixture of two molecules of p-toluidino and one molecule
of aniline :
C 6 H 5 NH 2 + 2C 7 H 7 NH 2 + 30 = 2H 2 O +C 20 H 21 N 8 O.
This equation proved to be insufficient when Coupier
succeeded in preparing a red dyestuff by oxidising tolui-
dine free from aniline, which he had obtained from pure
toluene. Coupler's discovery appeared to contradict
Hofmann's statement that pure toluidine does not
give a red on oxidation. Rosenstiehl repeated Coupler's
experiments, and confirmed his results, but found that
the pure toluidine obtained by reduction of pure nitro-
toluene was a mixture of the solid ^-toluidine previously
TPvIPHENYLMETHANE DYESTUFFS 155
known, and an isomeric liquid o-toluidine. Coupler's
red was hence obtained by oxidising a mixture of o- and
'/j-toluidine, whereas that of Hofmann was produced by
oxidising a mixture of _p-toluidine and aniline, and hence
they could not be identical. The constitution of these
red dyes tuffs still remained unknown. Hofmann, Paraf
and Dale, Caro and Wanklyn, acted on rosaniline with
nitrous acid, and obtained a true diazo-coinpound which
on boiling with water evolved nitrogen and gave a product
similar to rosolic acid. In the course of a notable research
E. and 0. Fischer (Ann., 1878, 194, 242) established the
constitution of Magenta in the following manner :
The dycstuff obtained by oxidising a mixture of p-toluid-
ine and aniline, C 19 H 17 N 3 HC1, was treated with alkali,
and gave the base C 19 H 17 N 3 H 2 or C 19 II 19 N 3 O, called
pamrosaniline, which loses its oxygen on reduction to
give a leuco-base, C 10 H 19 N 3 , paraleiicaniline. Paralenc-
anilino is a triamino, C 19 IF 13 (XH 2 ) 3 , as on diazotising
and boiling with alcohol, the NH 2 groups are replaced
by three atoms of hydrogen giving a hydrocarbon,
C 19 H 16 , which is really triphenylmetliane CH(C 6 H 5 ) 3 .
In the same manner, tlio Magenta formed by oxidising
one molecule of p-toluidino, one molecule of o-toluidine
and one molecule of aniline, having the composition
C 20 H 19 N 3 HC1, gives a base rosaniline, C 20 H 21 N 3 O, which
on reduction ^yields leucaniline, C 20 H 21 N 3 . After diazo-
tisation this compound yields on boiling with alcohol the
hydrocarbon C 20 H 18 , which is dipheuyltolyl methane :
H-O r C r> H 5
\3 6 H 4 CH 3
Having detormiued the constitution of the original
hydrocarbons by this degradation process, they com-
pleted their research by conducting the synthesis of the
dyestuffs. On treatment with nitric acid, triphenyl-
metliane (I.) gives a trinitrotriphenylinethane which is
!5C ORGANIC DYESTUFFS
converted by reduction into triumidolriphenylmothauo,
(II.), mid this is identical \rith paraleucaniline :
a.) ,c 6 H 4 xo, (ii.) cyi 4 NH, (in.)/ i 6 rr 4 NH.
OH C 6 H 4 XO,-> CH CJ I 4 NH 2 -> C C 6 H 4 XI I.,
\ \ I \
V P H NO M 1 H NH ^P T-T IVH
<^ 6 n 4 rNU 2 ^0^4 ^-"2 OH ^8-"-4 i>(1! 2
On oxidation this gives the carbinol pararosaniline
(III.), the hydroehloride of which has the following
formula :
C C 6 H 4 NH 2 O-CH
\ \
C 6 H 4 = NHoCl C 6 H 4 = NH,C1
l j ararosaiiiline hydrochlorido. Rosaiiiline hydrochlorido.
Hofmami's commercial Magenta, containing C 20 , was
hence the higher homologue of pararosaniline, viz. rosani-
line, and Coupler's Magenta was the next higher homologue.
This idea of homologues of the rosanilines was developed
by the researches of Rosenstiehl and Gerber (Ann. da
chem. et phys. (5) 8, 176) and of Nolting. These homo-
logues possess almost identical shades and very similar
properties. To definitely establish the constitution of the
rosanilines, it only remains to determine the position of
the amido-groups in the phenyl rings, In the prepara-
tion of the rosanilines, ^p-toluidine is essential, as it is
its methyl-group which yields the carbon atom of the
methane residue. Hence, it follows that in rosaniline
at least one NH 2 group should be in ^-position to the
methane carbon atom. The numerous syntheses of the
rosanilines and their derivatives have shown that in these
dyestuffs all three amido-groups are in ^-position to the
central carbon atom. The formulae of pararosaniline and
rosaniline are as follows, being, according to Baeyer's
nomenclature, diamidofuchsonimonium chloride and
diamidomethylfuchsonimonium chloride.
TRIPHENYLMETHANE DYESTUFFS 157
/> c <
Pararosaniline
hydrochloride.
> c
Rosamline
hydrochloride.
Manufacture of Magenta.
Magenta is manufactured by three processes :
(1) Oxidation of a mixture of aniline and toluidine
by means of arsenic acid.
(2) Oxidation of the same mixture \>y nitrobenzene.
(3) The synthetic formaldehyde process.
(1) Arsenic Acid Process. (See Ch. Lauth, Diet, de
Wurtz, and Mulhauser, Dingier, 1887, 266, 455, 503,
54T.) The mixture of aniline and toluidines used for
the manufacture of Magenta is called " aniline oil for
rod." It is obtained by mixing one part of aniline with
t\\v> parts of toluidine containing 36 per cent, of para-
and C4 per cent, of or^o-toluidine. The average
158
ORGANIC DYESTUFFS
composition of aniline oil for red is : aniline 33 per
cent., jp-toluidine 23 per cent., o-toluidine 44 per
cent. The theoretical proportions necessary are those
of an equimolecular mixture, containing aniline
30 per cent., o-toluidine 35 per cent., p-toluidine
35 per cent., but an excess of o-toluidine increases
the yield.
570 kilograms of syrupy arsenic acid (SP. GR. 2-05)
and 340 kilograms of aniline oil for red are placed in
a cast-iron vessel fitted in the lower portion with a large
FIG. 5.
inclined pipe for emptying. The vessel is closed by a
cover carrying several openings (Fig. 5) for the axis
of the stirrer, a tube for the thermometer, an inclined
pipe leading to a condenser, and an opening for taking
samples. The apparatus is heated by direct fire or
in an oil bath first to 120 and then with constant
stirring to 180-190 in seven hours. Water distils off,
carrying oil with it, and this is called Magenta echappfa.
When half of the oil has distilled off, and a sample
solidifies on cooling, the product is run off into wooden
tanks.
TRIPHENYLMETHANE DYESTUFFS 159
The Magenta echappes are separated from the water,
and are used for the manufacture of azo -compounds
and of Safranine : they contain very little ^-toluidine
and can no longer be used for the manufacture of
Magenta. Their composition id : about 70 per cent,
o-toluidine, 29 per cent, aniline, and a small amount
of 2>-toluidine.
The mass resulting from the oxidation contains, in
addition to Magenta, other soluble and insoluble pro-
ducts. It is crushed and placed in an extractor con-
sisting of a horizontal cylinder fitted with a stirrer and
covered with a round lid. 2500 litres of water are
introduced into the extractor containing the crushed
mass, the stirrer set in motion and the vessel sealed ;
steam under pressure is then passed in to raise the
temperature to 120-130. After some time, the passage
of steam is stopped, and the liquid allowed to stand
until the pressure in the apparatus has fallen to one-third
that of the atmosphere. The liquid is then passed
through filter presses, which retain insoluble products,
and the filtered liquid is placed in tanks ; it contains the
arsenate and arsenite of rosaniline in addition to other
soluble dyestuffs, such as Chrysaniline. Twelve kilograms
of hydrochloric acid are added to keep the Chrysaniline in
solution, fifty kilograms of common salt added to convert
the arsenate and arsenite into the chloride, and the
liquid allowed to cool. Magenta is deposited in crystal-
line cakes, and this crude product must be purified.
The mother liquors are heated to 40 and neutralised
with sodium carbonate, which precipitates a dyes tuff,
Cerise, as a resinous mass, which is separated, and the
liquid which contains echappds in solution is made
alkaline with lime and the bases separated by steam
distillation. The crude Magenta is dissolved in 2500
litres of water, and the solution heated to the boiling
point in the course of half an hour. Ten kilograms of
calcined sodium carbonate are added in small portions
to precipitate the Mauveines, which are deposited in the
160 ORGANIC DYESTUFFS
form of resins arid may bo separated. The solution
will now only contain Magenta and Chrysaniline, and is
heated for one hour, decanted, filtered, and then eighteen
kilograms of hydrochloric acid and twenty-five kilograms
common salt added, the whole being transferred to the
crystallising tanks. On the surface of these are placed
wooden sticks, on which the Magenta is deposited in large
crystals ; after standing for two days and three nights,
the mother liquor is run off and the crystals sorted and
dried. The largest crystals form Diamond Magenta or
Magenta 00. The yield of Magenta crystals is not
more than 35 per cent, of the weight of aniline oil for
red used.
(2) Nitrobenzene Process. The apparatus used is
similar to that of the preceding process, except that the
vertical portion of the pipe leading to the condenser
is somewhat longer, in order to allow the condensed
liquid to flow back into the heating vessel. Two -thirds
of the amount of aniline oil for red to be used are first
neutralised with hydrochloric acid, the salt dried, and
heated to 130-140. The remaining third of the aniline
oil for red is added and then an amount of nitrobenzene
equal to one-half the total amount of aniline oil for
red used. The liquid is gradually heated to 190 with
addition of a quantity of iron filings amounting to 5 per
cent, of the weight of the aniline oil. Water and
echappes, consisting of nitrobenzene and a mixture of
aniline and o-toluidine, distil from the end of the
condenser. The progress at the reaction is followed by
taking samples, and when it 'is finished, a current of
steam is passed in through the axis of the stirrer to
separate the remainder of the oils. The pasty mass is
allowed to run into boiling water, to which has been added
hydrochloric acid and salt, when the bases in the product
dissolve as hydrochlorides, but the Magenta remains
insQ v V1 The liquid is decanted, neutralised with lime,
^AlAlifieS On T i MI -i rrn nr i T.J l
, i distilled. The Magenta is obtained as an
mass with bronze reflex, which is purified as
TRIPHENYLMETHANE DYESTUFFS 161
in the arsenic acid process. It is naturally freo from
arsenic, and the yield is somewhat higher, being about
42 per cent. In the commercial process, nitrotoluene is
used, larger yields being obtained.
In the two processes outlined above, a mixture of
pararosaniline and rosaniline is obtained, the former by
oxidation of one molecule of ^-toluidine and two mole-
cules of aniline,
C ' H 4<NH 3 2 + 2C 6 H 5 NH 2 +30 = 3H 2 0+C 19 H 17 N 3 ,
and the latter from one molecule of ^-toluidine, one
molecule of aniline, and one molecule of o-toluidine.
2 2) + 3
= 3H 2 + C 20 H 19 N 8 .
The necessary oxygen is obtained either by the con-
version of the arsenic acid into arsenious acid, or from
the nitrobenzene. In the latter case, the reaction is more
complex, as the iron salts act as oxygen carriers, the
ferrous chloride formed being oxidised by the nitro-
benzene to give ferric chloride, which is the active agent
in the oxidation of aniline oil for red. It would appear
that the aniline formed from the nitrobenzene does not
itself enter into the composition of the Magenta pro-
duced, for if the nitrobenzene is replaced by chloro-
nitrobenzene or a sulphonated derivative, chlorinated
or sulphonated rosanilines are not obtained.
Rosenstiehl and Nolting have found that all the higher
homologucs of ^)-toluidine yield rosanilines on oxidation
in presence of primary amines in which the meta- and
2?ara-positions are free.
3. Formaldehyde Process. By this process any of the
rosanilines may bo prepared in the pure state, and further,
it is easy to obtain the rosaniline derived from tritolyl-
methane, New Magenta, containing C 22 .
By the action of an aqueous solution of formaldehyde
on a primary base such as aniline or toluidine there is
O.D. L
162 ORGANIC DYESTUFFS
first formed a methylene derivative. Thus in the case
of aniline the following reaction occurs :
C 6 H 5 . NH 2 + OCH 2 = C 6 H 6 N : CH 2 +H 2 O,
dehydro -formaldehyde aniline or methylene aniline being
produced. On heating with an excess of aniline and
its hydrochloride, these methylene derivatives first form
the isomeric dehydro -amido-benzyl alcohols, which then
combine with a further molecule of aniline to give
diamidodiphenylmethane or its homologues (DM. P.
53>937, 54,848, 55,565, 87,934 (Hochst), 96,762 (Kalle) ).
NH
Homolka in 1882 and Walter in 1887 obtained Magenta
by oxidising a mixture of p-diamidodiphenylmethane
and aniline. In the Hochst Farbwerke (D.E.P. 61,146)
this oxidation is carried out by means of nitrobenzene
and iron* The dehydro-bases may also be converted
into dyestuffs directly by heating with an excess of
aniline or another base or their hydrochloride, nitro-
benzene and ferric chloride, the oxidation being repre-
sented by the following equation :
= C C 6 H 4 NH 2 + 2H 2
\3 6 H 4 NH 2
By entirely or partly replacing the aniline by o-tolui-
dine, homologous Magentas containing C 20 , C ai , C 22 , etc.,
may be obtained.
TRIPHENYLMETHANE DYESTUFFS 163
Other Synthetic Mdhods. Leuco-bases of the Magenta
series may be obtained by condensing ^-nitrobenzalde-
hyde with aniline or o-toluidine in presence of zinc
chloride, the nit ro -compound produced being then
reduced. Another method is to act on aniline with
jp-nitrobenzylchloride, jp-nitrobenzo trichloride, or^-nitro-
benzyl alcohol.
General Properties of the Rosaniline Series.
Most of the reactions of the Magenta series are common
to all the amido- and alkylamido-tripheny line thane
dyestuffs.
Action of Reducing Agents. Reduction converts the
dyestuffs into the colourless leuco-bases, but these yield
the dyestuff again on oxidation ; the action of the air
is not sufficient to cause the reappearance of the original
colour.
Action of Oxidising Agents. The triphenylmethane
dyestuffs are destroyed by oxidising agents. According
to Georgievics, pararosaniline yields diamido-benzo-
phenone. It is for that reason that it is essential not
to use more than the theoretical amount of lead dioxide
in oxidising leuco-bases.
Action of Acids. The colour bases (carbinols) give
the mono-acid salts with acids, these forming the dye-
stuffs, whereas excess of acid gives yellow salts. Warm
dilute acids bring about the hydrolysis of the dyestuffs.
Concentrated sulphuric acid acts as a sulphonating agent,
but this process occurs best with the leuco-bases. On
treatment with nitrous acid the rosanilines give diazo-
compounds, and these on boiling with water give rosolic
acids.
Action of Alkalies. The dyestuffs derived from tri-
amidodiphenylmethane are decolourised by alkalies
owing to the formation of the carbinol bases. This
conversion is not instantaneous, and has be'
164 ORGANIC DYESTUFFS
to agree with the quinonoid theory, a coloured quinonoid
ammonium base being first produced, which is slowly
converted into the colourless carbiuol :
C 6 H 4 NH 2 C 6 H 4 NH 2
C 6 H 4 NH 2 -* C C 6 H 4 NH 2
^ W % H
C 6 H 4 = N< C 6 H 4 =N<g
Cl OH
/ C 6 H 4 -NH 2
-> C C 6 H 4 NH 2
I H \C 6 H 4 -NH 2
This has been found by Homolka, and proved more
exactly by a study of the conductivity of the salts in
presence of caustic alkali by Hantzsch and Osswald
(Ber., 1900, 33, 278, 753).
Action of Ammonia. This has been shown by Villiger
and Kopetschni (Ber., 1912*, 45, 2910) to yield, not
carbinols, as was previously considered, but amines of
the type R 3 =C . NH 2 , which are not much different
from the carbinols, being stable to alkalies, but yielding
ammonia on treatment with alcohols, thus :
R 3 =C NH 2 + C 2 H 5 OH - R 3 ^C OC 2 H 5 + NH 3 .
Action of Light. The triphenylme thane dyestuffs are
not very resistant to the action of light, and hence the
shades obtained are not fast.
Pararosaniline hydrochloride has the formula :
C 6 H 4 NH 2
G-0 6 H 4 NH 2
C 6 H 4 =NH. HC1
TRIPHENYLMETHANE DYESTUFFS 165
It is slightly soluble in water, from which it forms
crystals with a metallic reflex, which contain 4H 2 O
(Schultz, Die Chemie des Steinkohlenteers, 3rd edition,
vol. ii., p. 165). It is present in ordinary Magenta.
Magenta. The hydrochloride crystallises in large
octahedra with a metallic reflex
C 6 H 4 -NH. HC1
S
C C 6 H 4 -NH 2
C 6 H 3 (CH 3 )NH 2
New Magenta is the hydrochloride of triamidotritolyl-
carbinol, and is obtained by the formaldehyde process
(D.E.P. 59,775).
C 6 H 3 (CH 3 )-NH 2
G-C 6 H 3 (CH 3 ) NH 2
C 6 H 3 (CH 3 )=NH. HC1
It is a crystalline powder which differs from the
preceding dyestuffs in its greater solubility in water.
The Rosanilines are red basic dyestuffs which dye wool
and silk direct, and also dye cotton mordanted with
tannin. The sulphonic acids obtained by sulphonating
Magenta, or, better, rosaniline, are acid dyestuffs which
dye wool and silk from an acid bath. The sodium and
ammonium salts have the names Magenta S, Acid
Magenta, etc.
Alkylated Derivatives of the Rosanilines.
The substitution of a methyl group for one or more
hydrogen atoms of the rings yields higher homologues
of pararosaniline without changing the shade of the
product. This is not the case, however, if one or more
alkyl radicles are substituted for the hydrogen atoms
166 ORGANIC DYESTUFFS
of the amido-gyoup ; the shade is considerably modified
and it becomes more violet the greater the number of
hydrogen atoms replaced. Thus hexamethylpararos-
aniline hydrochloride, Crystal violet, gives pure violet
shades.
C 6 H 4 -NH 2 C 6 H 4 -N
/ /
C C 6 H 4 NH 2 -v C C 6 H 4 N
I
01
Cl
Pararosaniline. Crystal violet.
General Methods of Preparation. The alkylated deri-
vatives are obtained by methods which can be applied
generally :
(1) The oldest method, used by A. W. Hofmann for
first preparing the Aniline violets, consists of heating
the rosaniline with alkylogens, for example :
C 6 H 4 -NH 2
HO C C 6 H 4 NH 2 + 3CH 3 C1 + SNaOH
C 6 H 4 -NH 2
C 6 H 4 NHCH 3
= HO C C 6 H 4 NHCHL + 3NaCl + 3H 2
C 6 H 4 NHCH 3
Using methyl iodide or bromide, the substitution may
be carried as far as the hexamethyl-derivative, and with
ethyl esters, tri- or tetra-alkylated derivatives may
be obtained.
(2) Tetraalkyldiamidobenzophenones are condensed
with tertiary amines in presence of phosphorus oxy-
TRIPHENYLMETHANE DYESTUFFS 167
chloride or carbonyl chloride. In the latter case, the
carbonyl chloride may be allowed to act directly on a
tertiary base.
C 6 H 4 -NR 2
C0< + C G H 5 NR 2 + COC1 2
C 6 H 4 NR 2
C 6 H 4 -NR a
= C0 2 + HC1 + C C 6 H 4 NR 2
C 6 H 4 =NR 2
i,
(3) Tetraalkyldiamidobenzhydrols are condensed with
tertiary bases, the leu co-bases so obtained being oxidised :
C 6 H 4 -NR 2
HC iOH + HC,H 4 NR a
C 6 H 4 NR a
C 6 H., NR 2
= HC C 6 H 4 NR 2 + H 2 O
CH 4 -NR 2
This process may be modified by oxidising a mixture
of a tertiary base and a tetraalkyldiamidodiphenyl-
methane.
(4) A dialkyl-p-amidobenzaldehyde is condensed with
two molecules of a tertiary amine and the leuco-base
oxidised.
(5) Ethyl oxalate is condensed with secondary or
tertiary amines in presence of aluminium chloride
(A. Guyot, Bull. Soc. chim., 1907, 1, 937).
168 ORGANIC DYESTUFFS
Methyl tiolet.
The formation of violet dyestuffs by alkylation of
rosaniliiie was observed by Kopp in 1861, and studied
in 1864 by A. W. Hofmann, who obtained Iodine violet
or Hofmann's violet by the action of ethyl iodide on
rosaiiiline. As the rosaniline which he used contained
pararosaniline, the dyestuff obtained \vas a mixture of
triethyl-rosaniline and triethyl-pararosaniline. This pro-
cess was soon afterwards replaced by the one discovered
by Lauth in 1866 and carried out by the firm of Poirrier
at Saint-Denis, which consisted of oxidising dimethyl-
aniline in presence of copper salts. In this manner the
use of the very expensive iodine is avoided, and it is not
necessary to first prepare rosaniline.
A mixture is made consisting of a copper salt (nitrate,
sulphate or chloride), common salt, sand, dimethyl-
aniline, and an acid, and heated to about 40-60, when the
formation of the dyestuff commences immediately and
the mass assumes a metallic lustre. When the reaction
is finished, the mass is extracted with water and the
dyestuff precipitated by addition of salt. The yield
obtained is from 70 to 75 per cent, of the weight of
dimethylaniline used.
Fischer has shown that, during the oxidation of the
dimethylaniline, formaldehyde and formic acid are also
produced (E. and 0. Fischer, Ber. 9 1878, 11, 2098 ;
1883, 16, 2909), and hence the formation of the violet
dyestuff may be explained by one of the methyl groups
of the dimethylaniline yielding formaldehyde, whilst
monomethylanUine remains :
C 6 H 3 N< 3 + = C 6 H 6 NH CH 9 + CH 2 0.
The formaldehyde then condenses with the dimethyl-
aniline and the monomethylaniline, giving derivatives
of diphenylrnethane, and these are oxidised in presence
of an excess of base, forming mixtures of tri-, tetra-,
penta-, and hexa-methyl-pararosaniline. According to
TRIPHENYLMETHANE DYESTUFFS 169
the proportions of the various products, a more or less
violet dyestuff is obtained.
Crystal violet (hexamethyldiamidofuchsonimonium
chloride). This dyestuff is prepared by one of the general
methods. It forms brilliant green crystals containing
9H 2 0, and on reduction it gives hexamethyl paraleuc-
aniline, which forms white plates of M.P. 173.
By the action of methyl chloride on an alcoholic
solution of Methyl violet, the liquid being kept neutral,
the methyl chloride compound of hexamethyl-pararos-
aniline is obtained. It is a green dyestuff, which was
discovered by Hofmann, and manufactured by Lauth
and Baubigny in 1871. It is called Methyl green^ and
has the following constitution :
C 6 H 4 ~N(CH 3 ) 2
C 6 H 4
I CH 3
Cl
Benzylated Derivatives. By the action of benzyl chloride
on Methyl violet, Lauth, in 1868, obtained Benzyl violet.
The dyestuffs containing benzyl groups are easily
sulphonated, and to the class of substances so
obtained belong Acid violet 65, 105, etc., and the
Formyl violets, one of which is prepared by condensing
formaldehyde with ethylbenzylaniline sulphonic acid and
oxidising in presence of dicthylaniline.
Phenylated Derivatives of the Rosanilines.
In 1861 Ch. Girard and de Laire prepared the first
phenylated derivatives of Magenta by heating the salts
of rosaniline with aniline to 160, when violet and blue
dyestuflk were obtained which they patented in France
and in England (B.F. 2nd January, 1861). Their manu-
facture was undertaken by the Fuchsine Company at
170 ORGANIC DYESTUFFS
Lyons, and by Simpson, Maule, and Nicholson in London.
The process was slightly modified by the addition of
various condensing agents, such as acetic acid, benzoic
acid, etc. Later in 1867, Girard and de Laire succeeded
in converting diphenylamine directly into Aniline blue
by heating with oxalic acid at 110-120. It was, how-
ever, Hofmann who established the constitution of these
dyestuffs by showing that the formation of these violet
and blue compounds from rosaniline is due to the
substitution of one, two, or three phenyl groups for
the hydrogen atoms of the amido-groups. Whereas the
monophenyl-derivative is violet, the diphenyl-derivative
is bluish violet, and the triphenyl-derivative is a slightly
greenish blue dyestuff. As the rosanilino used for its
preparation is mixed with pararosaniline, the blue dye-
stuff obtained is really a mixture of the phenyl deriva-
tives of the two bases. The action of aniline on
rosaniline may be represented by the equation :
,C 6 H 4 NH 2 HNH-C 6 H G
HO (>-C 6 H 4 NH 2 HNH C 6 H 5
\2 6 H 8 -NH 2 + HNH-C 6 H 6
CH 3
/ C 6 H 4 -NH-C 6 H 5
= HO C-C 6 H 4 NH C 6 H 5 + 3NH 3
\C 6 H 3 -NH C 6 H 5
CH 3
The shade of blue obtained is much purer than that of
the original dyestuffs. It is essential to use aniline free
from toluidines, as the dyestuffs obtained from the
toluidines have a redder shade, and it is for this reason
that pure aniline is sometimes still termed at the present
time " aniline oil for blue " to distinguish it fron\ " aniline
oil for red."
Up to the present, it has not been found possible to
TRIPHENYLMETHANE DYESTUFFS 171
introduce more than three phenyl groups into rosaniline.
The salts of the bases so obtained are blue dyestuffs
which are insoluble in water but soluble in alcohol.
In order to make these dyescuffs soluble it is necessary
to sulphonate them ; the free sulphonic acids are coloured
and are insoluble in water but soluble in alkalies, giving
colourless solutions of the alkali salts of the sulphonic
acids of the carbinols. These are coloured in contact
with acids, and constitute the Alkali blues of commerce.
Derivatives of Pararosaniline.
The monophenyl- and monotolyl-derivatives occur
together with the diphenyl- and ditolyl-derivatives in
the dyestuffs known as Phenyl violet, Imperial violet,
Regina violet, Lyons blue, etc., being also mixed with the
corresponding derivatives of rosaniline. They are ob-
tained by heating rosaniline prepared by the arsenic
acid method with the Magenta echappes formed at the
same time, at 120 in presence of acetic acid.
Diphenylamine blue, triphenylpararosaniline hydro-
chloride : .C 6 H 4 NH C 6 H 5
C-C 6 H 4 -NH-C 6 H 5
is considered to be present, together with its higher
honaologue, in Aniline blue. It is obtained by heating
aniline with pararosaniline and a condensing agent (an
organic acid), by heating diphenylamine with perchlor-
ethane (C,,C1 ) or by heating diphenylamine with oxalic
acid at 120. In the last reaction, the oxalic acid yields
the carbon atom for the methane residue by a process
which is still unknown ; the yield is very small, being
about 10 per cent. Baeyer and Villiger (Ber., 1904, 37,
2870) have been able to detect the presence of triphenyl-
pararosaniline in Diphenylamine blue.
172 ORGANIC DYESTUFFS
Diphenylamine blue is also known under the name of
Spirit Sky blue or Bavarian blue. It is insoluble in water,
and only slightly soluble in alcohol. Its sulphonic acids
were prepared by Nicholson in 1862, and were the first
sulphonic acid dyestuffs known. The trisulphonic acid
is called Soluble Sky blue,. Cotton blue, or Helvetia blue, and
was prepared by Sandmeyer by condensing diphenyl-
amine sulphonic acid with formaldehyde, and oxidising
the diphenylmethane derivative produced in presence of
a further molecule of the sulphonic acid (D.li.P. 73,092,
73,178, 76,072, 77,318).
Whereas Alkali blue XG, the monosulphonic acid of
/3-naphthyl-pararosaniline, was not of great importance,
Soluble blue XG, the trisulphonic acid, is valuable owing
to the brilliancy and purity of its shade, and is com-
mercial as the Titan Comos [H.], Isamine blue [C.],
Benzo Brilliant blue [By.], etc. Unfortunately, as is the
case with all the Triphenylmethanes and Phthaleins,
this dyestuff is not very fast to light.
Derivatives of Rosaniline.
The most important dyestuffs of this group are
Aniline blue, also known as Spirit blue, Gentian blue,
Opal blue, or Light blue, and its sulphonic acids.
It is prepared by heating 250 kilograms of aniline,
25 kilograms of rosaniline, and 3 kilograms of benzoic
acid in a cast-iron vessel fitted with a stirrer and
heated in an oil-bath or by direct fire. The aniline,
rosaniline and five-sixths of the benzoic acid are first
introduced and heated to 180, and then the remainder
of the benzoic acid added. An energetic reaction
occurs, ammonia is liberated and aniline distils off.
When samples taken show that the reaction is complete,
the mass is run into dilute hydrochloric acid, which
dissolves the excess of aniline and rosaniline, the Aniline
blue remaining insoluble, and this is filtered off, washed,
and dried. A small amount remains in the mother
TRIPHENYLMETHANE DYESTUFFS 173
liquors, which are treated with lime and distilled to
obtain the aniline. (See Schultz, Chem. des titein-
kohlenteers.) Thirty-four to thirty-five kilograms of
Aniline blue (theoretical 44-3) are obtained from twenty-
five kilograms of rosaniline. In this reaction the exact
part played by the benzoic acid is not known.
In the pure state, Aniline blue forms green crystals
which are soluble in alcohol to a blue solution.
This dyestuff was supposed to be triphenylrosaniline
hydrochloride, but Baeyer and Villiger (Ber., 1904, 37,
2870) have shown that the Aniline blue of commerce
consists of almost pure diphenylrosaniline, and that
triphenylrosaniline cannot be prepared by the action of
aniline on rosaniline ; this has been confirmed by Knecht
(J. Soc. Dyers and Col, 1907, 119).
Aniline blue is easily sulphonated even by ordinary
sulphuric acid, and as rosaniline can only be sulphonated
with difficulty, the sulphonic groups are supposed to enter
the substituted phenyl radicles. The sulphonation was
first carried out by Nicholson, and the sodium salt of the
rnonosulphonic acid is known as Alkali blue or Nicholson \s
blue. The free acid is blue and insoluble in water, whereas
the alkali salts are colourless, probably being carbinols :
C 6 H 4 -NH-C 6 H 4 -S0 3
v \ - - VM* 3 -fNaOH
XH 4 -NH-C 6 H 5
Blue acid anhydride.
,C 6 H 4 NH C 6 H 4 S0 3 Na
/
Colourless sodium salt.
The alkali salt dyes wool from a bath containing
sodium borate or phosphate, but the fibre so treated is
only of a slightly bluish grey colour, and must be
174 ORGANIC DYESTUFFS
developed by passing through a bath of a dilute mineral
acid, to convert the carbinol into the free acid, or, better,
into its coloured anhydride.
More energetic sulphoiiation gives the disulphonic
acid, or Soluble Silk blue, and then trisulphonic or
tetrasulphonic acids, the Soluble Cotton blues, which are
soluble in water and are used for dyeing wool and silk
from an acid bath, and for dyeing cotton mordanted with
tannin or alumina.
Triamido-derivatives of Diphenylnaphthylmethane.
The general methods used for the preparation of the
alkylated derivatives of triphenylmethane may be
extended to those of diphenylnaphthylmethane. To
this group belong the following dyestuffs :
Victoria blue, obtained by condensing tetramethyl-
diamidobenzophenone chloride with phenyl-a-naphthyl-
amine.
Night blue. Ketone base is condensed with y-tolyl-
a -naphthylam ine .
Both these basic dyestuffs dye wool and tanned cotton
a pure blue (Kern and Caro, D.R.P. 29,060 ; Nathansohn
and Miiller, Ber., 1889, 22, 1891).
New Victoria blue is produced by the condensation
of Michler's hydrol with othyl-a-naphthylamine.
HYDROXY-DERIVATIVES OF TRIPHENYLMETHANE.
Just as fuchsonimine is the chromogen of amidotri-
phenylmethane dyestuffs, fuchsone is the chromogen
of the hydroxy-derivatives. It is readily prepared by
heating p-methoxytriphenylmethane to 180-200, when
methyl chloride is split off :
I
01
CH 3 C1
TRIPHENYLMETHANE DYESTUFFS 175
Bistrzycki and Herbst, who first isolated this product,
called it diphenylquinomethane (Ber., 1903, 36, 2333).
Baeyer, Villiger and Hallensleben (Ber., 1903, 36, 2791)
prepared it by heating ^-hydroxytriphenylcarbinol in
a current of hydrogen, when it loses a molecule of water.
Baeyer has suggested the name fuehsom for this com-
pound. It forms brown crystals of M.P. 167-168.
The hydroxy-dyestufls are derived from fuchsone by
the introduction of further hydroxy-groups in para-
position. The simplest is Benzaurine or hydro xyfuchsone,
discovered by Dobner (Ber., 1879, 12, 1462 ; 1880, 13,
610) by heating benzotrichloride with phenol. It has
the following constitution :
Benzaurine dissolves in alkalies, forming an intense
red solution.
A new series of dyesluffs which are very fast to alkali,
due to the presence of a substituted group in ortho-
position to the methane carbon atom, has been prepared
by A. Conzetti, by the condensation of or^o-substituted
benzaldehydes with salicylic or eresotinic acid by means
of sulphuric acid, and then oxidation by means of
nitrosyl sulphate. From benzaldehyde o-sulphonic acid
and o-cresotinic acid, there is produced Erio Chrome,
cyanine B : CH
HOf
Hoool k A X COOH
176 ORGANIC DYESTUFFS
which gives a brick -red shade on wool, which turns to
a violet-blue on after-chroming.
Erio Chrome Azurol B is prepared from o-chlorobenzal-
dehyde, and Chromazurol 8 from o-chlorobenzaldehyde
sulphonic acid. The Chromoxan colours are similar
dyestuffs derived from aldehydes of the naphthalene
series.
The most important compounds are the :
Trihydroxy-derivatives.
Historical. In 1834 Bunge obtained a red dyestuff,
by oxidising crude phenol, to which he gave the iiamo
rosolic acid. Later Kolbe and Schmidt, in 1859, pie-
pared a similar red dyestuff by treating phenol with
oxalic acid in presence of warm sulphuric acid ; they
considered this product to be different to rosolic acid
and called it Aurine. In 1866, Caro and Wanklyn
showed the relationship of these dyestuffs to Magenta.
By decomposing diazo-rosaniline with water, they
obtained a red dyestuff which they believed to be
identical with Runge's rosolic acid, and hence different
from Aurine. In 1887, however, Dale and Schorlommer
succeeded in converting Aurine into rosaniline, which
seemed to show that rosolic acid was identical with
Aurine. It was only when the researches of Fischer
had established the constitution of rosaniline, and the
idea of homologues of rosaniline had been suggested
by Rosenstiehl, tkat the difference between Aurine and
rosolic acid was recognised. This difference is the same as
that which exists between pararosaniline and rosaniline,
rosolic acid being the higher homologue of Aurine.
Diazotisation of pararosaniline gives Aurine, and diazo-
tisation of rosaniline gives rosolic acid. The trihydroxy-
carbinols are not known, as they immediately lose a
molecule of water to give the dyestuffs :
TRTPHENYLMETHANE DYESTUFFS 177
HO C C 6 H 4 NH 2 +HNO 2
\C 6 H 4 -NH a
Pararosaniline.
/C 6 H 4 OH /C 6 H 4 OH
HO C C 6 H 4 OH = C C 6 H 4 OH +H 2 O
\C 6 H 4 OH V) 6 H 4 =
Aurine.
Aurine, pararosolic acid, or Yellow corallin is formed
together with rosolic acid and many other products by
heating phenol with a mixture of sulphuric and oxalic
acids for twenty-four hours at 120-130. As has been
described, it is also obtained by decomposing diazo-
pararosaniliiie with water. It forms red crystals which
are soluble in alcohol and acetic acid to a yellowish-red,
and in alkalies to a magenta coloured solution. Reduc-
ing agents convert it into leuco-Aurine or trioxytri-
phenylmethane.
By heating crude Aurine under pressure with ammonia,
Guinon, Manias, and Bonnet of Lyons obtained a red
dyestuff, Paeonine or Red corallin ; by heating Aurine
with aniline, a blue dyestuff, Azuline, is produced.
Rosolic acid is obtained by oxidising a mixture of
cresol and phenol in presence of sulphuric acid by means
of arsenic acid. A simpler method is to diazotise
rosaniline and boil the diazo-compound with water.
Rosolic acid crystallises in red prisms, which are soluble
in alkalies to an intense red solution. All these com-
pounds are now almost entirely used in the form of lakes
in printing wall-papers.
PhenolphtJialein * is a hydroxy-carboxylic acid dye-
stuff which may be compared with Aurine. Baeyer has
*Most authors place pheiiolphthalem among the phthalems,
derived from fluorane ; it is convenient to consider it imme-
diately after the hydro xy -derivatives of triphenylmethane,
O.P. * w
178 ORGANIC DYESTUFFS
given the name " phthaleins " to the compounds which
are formed when phthalic anhydride is condensed with
phenols. In the case of phenol the reaction is :
/ co \
6 H 4 O + 20 6 H 6 OH
XKT
OH
OH
Phenolphthaleiri is the hydroxy-derivative of phthalo-
phenone, which is obtained by condensing phthalyl
chloride with benzene in presence of aluminium chloride.
C 6 H / \0 + 2C 6 H 6
CO
C fl H 4 + 2HC1
Phenolphthalein and most of the phthaleins derived
from it are colourless ; on reduction they yield phtha-
lines, which are hydroxy-carboxylic acids derived from
triphenylmethane :
CTT HIT
6 ri 4 un
C C 6 H 4 OH C 6 H 4 -
Cf{ \ + H, - I
V COOH
TRIPHENYLMETHANE DYESTUFFS 179
The phthaleins dissolve in alkalies to form very intense
reddish- violet solutions, which are decolorised even by
very weak acids, such as carbonic acid. The salts formed
contain two atoms of a monovalent metal, and their
colour has been explained by the quinonoid theory. The
alkali first breaks the lactone ring, then giving a salt of
the carbinol, as follows :
C 6 H 4 -OH
C^CgH, OH
C 6 H 4 +NaOH
C 6 H 4 OH
= C 6 H 4 C C 6 H 4 OH
OH
C0(
)ONa
In the same manner that trihydroxytriphenylcarbinol
loses water to form Aurine, this o-carboxylic acid of the
carbinol loses water, thus :
C 6 H 4 OH
C 6 H 4 C C 6 H 4 OH
COONa OH
/ C 6 H 4 -OH
= C 6 H 4 C=C 6 H 4 =0 +H 2
C001
)Na
and at the same time the remaining hydroxy-group
is converted into the salt. Kober and Marshall (Journ.
Amcr. C.S., 1912, 1424) have recently prepared the mono
sodium salt of phonolphthalei'n :
COONa
I C 6 1I 4 OH
OH
180 ORGANIC DYESTUPFS
Phenolphthalein should have a different constitution
in the free state than in the form of a salt, and this
tautomerism has been made the subject of a number of
researches which can only be mentioned. They include
the work of Haller and Guyot (Compt. rend., 1893, 116,
479 ; 1895, 120, 297), and of Friedlander, Meyer, etc.
The recent researches of Green and King (J3er., 1906, 39,
2365 ; 1907, 40, 3724), K. Meyer and Hantzsch (Ber.,
1907, 40, 3484), R. Meyer and Marx (Ber., 1907, 40,
3603 ; 1908, 41, 2446), have advanced very good argu-
ments in favour of the quinonoid theory. Green and
King have been able to show that the phthaleins give
coloured esters, in which the carboxyl group is esterified,
and which should hence have a quinonoid structure,
similar to that of the coloured salts ; thus :
Colourless esters of the lactone form have been known
for a long time. In addition a coloured ethyl ether of
tetrabromophenolphthalein is known which has a quino-
noid structure.
CHAPTER XVII.
XANTHENE DYESTUFPS.
THE name xanthene has been given to the internal
anhydride of o-dihydroxydiphenyhnethane :
H 2 -I- CH 2
The o-dihydroxy-derivatives of di- and of tri-phenyl-
methane easily lose a molecule of water, being converted
into xanthene derivatives. On oxidation xanthene
yields a ketone, xanthone, which is converted into
xanthhydrol by reducing agents. Xanthhydrol gives
salts with acids, and according to present ideas of the
basic properties of oxygen the halogen is considered to
be attached to the oxygen, which becomes tetrayalent.
^ ,
Xanthene.
^
><
6 H 4
Xanthone.
01
/O
H OH
Xanthhydrol.
CH'/
Xanthonium salt.
182 ORGANIC DYESTUFFS
This last compound is called xanthonium chloride, and
the formula given, which is in accordance with the
" oxonium theory," represents the oxygen atom as basic
and tetravalent. From the following it will be seen
that numerous analogies exist to the Thiazines, in which
the sulphur atom is tetravalent, and the compounds are
called thiazonium or azthionium derivatives. These
ideas were first suggested by A. G. Green (J.C.S. Proc.,
1892 and 1895) and have been developed by the
researches of Kehrmaim (Ann., 1902, 322, 1 ; 1910, 372,
287), Fosse, etc.
To obtain dyestuffs it is only necessary, as in the case
of di- or tri-phenylmethane, to introduce auxochromes in
y-position to the carbon atom of the methane residue
in xanthene, and to oxidise the leuco bases so obtained.
The general method for preparing these dyestuffs is to first
obtain a j5-disubstituted o-dihydroxy-derivative of di-
or tri-phenylmethane, dehydrate this product, and oxidise
the resulting compound ; thus tetramethyl-j9-diamido-
o-dihydroxydiphenylmethane first gives a xanthene
derivative :
OH
which on oxidising in acid solution gives the dyestuff.
Two constitutional formulae may be assigned to this
dyestuff, one, the ^pam-quinonoid formula, similar to that
of the triphenylmethane dyestuff :
XANTHENE DYESTUFFS iss
and the other, in which oxygen has become tetravalent,
giving an orJAo-quinonoid formula :
H ci
The formula according to the oxonium theory appears to
be the one most favoured.
Whichever formula may be adopted, there is present a
particular structure of carbon and oxygen atoms known
as the pyrone ring :
184 ORGANIC DYESTUFFS
hence these dyestuffs are often called Pyronines. The
Pyronines form fluorescent solutions.
Derivatives of Xanthene.
These compounds are of little importance. They
are obtained by condensing formaldehyde with two
molecules of a dialkyl-w-amidophenol, and dehydrating
the product by heating with concentrated sulphuric acid :
the diluted solution is then oxidised by means of ferric
chloride or nitrous acid (Biehringer, Journ. f. prakt.
Chem., 1896, 54, 217). Another method is to condense
formaldehyde with two molecules of an asymmetrical
dialkyl-w-phenylenediamine, cliazotise, boil with water,
and convert the o-dihydroxy-derivative into a xanthene
compound and into a dyestuff as previously described.
Pyronine G. [L.] was discovered by Bender in 1889
(D.R.P. 58,955 and 59,003) by condensing dimethyl-ra-
amidophenol with formaldehyde, dehydrating, and then
oxidising. Its constitution is as follows :
XANTHENE DYESTUFFS
185
It is a crystalline powder which is soluble in alcohol and
water to form a red solution with a yellowish fluores-
cence. It dyes silk and tanned cotton pink. On oxidis-
ing with permanganate it yields a new dyestuff called
Acridine red 5, of which the constitution is unknown.
Pyronine B is obtained by condensing formaldehyde
with diethyl-m-amidophenol.
Derivatives of Phenylxanthene.
In the preparation of the Pyronines, if the formalde-
hyde is replaced by an aromatic aldehyde, benzaldehyde
or its substitution derivatives, similar dyestuffs are
obtained, which are derivatives of phenylxanthene
(Farb. Bayer, D.R.P. 62,574). These dyestuffs were
discovered by Heumann and Rey (Ber., 1889, 22, 3001)
by heating benzotrichloride with dialkyl-m-amidophenol :
OH C 6 H 8 NR 2
CH.CC1
= C 6 H S .C
2HC1
6 H 3 -NR 2
These compounds are called Rosamines ; they are
basic dyestuffs which are more bluish than the Pyronines,
but are not of practical importance. The most important
dyestuffs are those which are related to both xanthene
and phthalophenone, that is to say, to the compound :
186 ORGANIC .DYESTUFFS
This compound has been called fluorane, and is formed
to a small extent together with phenolphthalein on
condensing phenol with phthalic anhydride. Its forma-
tion is explained by condensation in the ortho-position
due to dehydration, thus :
C =
+
Hi OffiD
o H ^ IOH =
C 6 H 4
/ >0
^ C-C 6 H 4
~ C 6 H 4 + 2H 2
0=0
Fluorane is a colourless crystalline substance of
M.P. 180. Its solution in sulphuric acid has a green
fluorescence.
Dyestuffs are obtained by introducing auxochromes
into the fluorane nucleus in the para-position. They
may be divided into hydroxy -derivatives or Phthaleins,
and amido- or alkylamido -derivatives, known as Rhod-
amines.
Phthaleins.
These are obtained by condensing phthalic anhydride
with phenols. Whereas phenol yields phenolphthalein,
which is a triphenylmethane derivative, m-dihydroxy-
benzenes give dyestuffs which are related to phenyl-
xanthene, fluorane, and triphenylmethane.
Fluoresce'in was discovered by Baeyer in 1871 by
heating phthalic anhydride with resorcinol to 200. For
XANTHENE DYESTUFFS
187
its commercial preparation, a mixture of resorcinol and
phthalic anhydride is heated in a cast-iron vessel to
180 and powdered zinc chloride added, when an ener-
getic reaction takes place ; the heating is continued
for ton hours at 190-200. The mass is dissolved in
caustic soda, and the dyestuff precipitated by means
of mineral acid. Fluorescein forms an orange powder
which decomposes at about 300, and dissolves in
alkalies, giving a solution with a strong green fluor-
escence ; its sodium salt is called Uranine [B.A.S.F.].
Reducing agents coiivert fluorescein into the colourless
fluorescine.
The constitution of fluorescein is given by its mode
of formation :
OH
+ 2H 2
As in the case of phenolphthalein, its salts have a
quinonoid constitution ; alkalies cause the hydrolysis
of the lactone ring, and the carbinol loses water as
follows :
ORGANIC DYESTUFFS
Nietzki and Schrotter (Ber., 1895, 28, 44) have been
able to show that both the isomeric esters exist, one
series being coloured and corresponding to the quinonoid
formula ; the others colourless, and related to the lactono
structure.
Uranine dyes wool yellow from an acid bath, and it
is used for printing wool.
Eosine is the tetrabromo-derivative of fluorescein, and
was discovered by Caro in 1874 at the Badische Anilin
und Sodafabrik, the process being kept secret. Its
constitution was established by Gnehm and Hofmann, arid
confirmed by Baeyer (Ann., 1876, 183, 1). It is obtained
by treating an alcoholic solution of fluorescein with
bromine, when the tetrabromo-derivative is precipitated
in a crystalline form, or by adding an alkaline solution
of bromine to an alkaline solution of fluorescein and
sodium chlorate. Eosine is commercial in the form of
XANTHENE DYESTUFFS
189
its sodium and potassium salts as Soluble Eosines. Their
constitution has been established by the following
reactions : on heating with caustic soda, Eosine gives
dibromoresorcinol and dibromodihydroxybenzoylbenzoic
acid, which has the following constitution :
CO Br
OH
CO OH
as on dehydrating it yields dibromoxanthopurpurin.
On the other hand, this dibromodioxybenzoylbenzoic
acid is converted by heating into Eosine and phthalic
anhydride. Hence in the form of its salts, Eosine has
the constitution :
NaOi
Br 1
fTO"
V\ // \}-
Cr
'Br
ONa
or
COONa
Eosine contains a carboxyl group which can be
esterified, the dyestuffs so obtained being of a purer and
more bluish shade, but their alkali salts are insoluble
in water. These are the Spirit Eosines or Eryihrines.
The ethyl ester is prepared by brominating fluorescein
190 ORGANIC DYESTUFFS
in alcoholic solution and heating under pressure. The
potassium salt is Spirit Primrose :
OK
C
c 8 H 4 <
COOC 2 H 5
It is a red dyestuff used for dyeing silk.
Erythrosines . These are iodo -derivatives of fluores celn ,
and were discovered by Nolting in 1875 by treating an
alkaline solution of fluorescein with an alkaline solution
of iodine. Di-iodo-fluorescein is called Dianthine or
Orient yellow, the alkali salts of tetra-iodo-fluorescein
form Soluble Primrose, Erythrosine B, etc.
By replacing the phthalic anhydride used in the pre-
paration of fluorescein by its halogen derivatives di- or
tetra-chlorphthalic anhydrides, di- or tetra-chlor-fluor-
escem is obtained. On treatment with bromine or
iodine, these compounds yield the corresponding Ery-
thrines or Erythrosines : thus di-chlor-fluorescein
yields on bromination Phloxine, of which the methyl
ester is Cyanosine :
eHBra ONa
C1 2 -C 6 H 4
COOCHg
Treatment with iodine yields Rose Bengal. Tetra-chlor-
fluorescein gives similar dyestuffs.
Oalleine is obtained by condensing phthalic anhydride
with gallic acid or pyrogallol ; thus it is a dioxy-
fluoresceln. It is a crystalline powder which dissolves
in alkalies to form a red solution, due to the proximity
XANTHENE DYESTUFFS 191
of the two hydro xy-groups. Galleme dyes on metallic
mordants, giving a beautiful violet on chrome mordant.
It is used in the form of a paste for calico-printing.
If Galleme is heated with concentrated sulphuric acid
at 200 it is converted into a new dyestuff, Cwrukine,
the salts of which are green ; this is also a mordant
dyestuff used in the printing of calico. Ccerulei'ne is a
derivative of anthracene, being formed as follows :
OH
Cceruleine S. is the bisulphite compound.
Rhodamines.
The name Rhodamines has been given to the alkyl-
amido-derivatives of fluorane. Symmetrical and
asymmetrical Rhodamines are known ; in the latter the
alkyl groups R and R' are different in the two benzene
nuclei, thus :
01
NB '
C 6 H 4 OOOH
192 ORGANIC DYESTUFFS
The symmetrical Rhodamines were obtained by
Ceresole in 1887 by condensing phthalic anhydride with
dialkyl-w-amidophenols. They can also be prepared by
converting fluorescem into the dichloro -derivative by
the action of phosphorus pentachloride, and acting on
this compound with dialkylamines.
no
The asymmetrical Rhodamines are produced by first
condensing a molecule of phthalic anhydride with a
molecule of a dialkyl-m-amidophenol, when a dialkyl-
amidohydroxybenzoylbenzoic acid is obtained :
COOH H
These acids may then be condensed with a further
molecule of a dialkyl-m-amidophenol different from the
first one used.
The Rhodamines are basic red dyestuffs of a remark-
ably pure shade, and with a strong fluorescence. They
dye wool and silk, and cotton mordanted with tannin.
Rhodamine B is obtained by condensing phthalic
anhydride with diethyl-w-amidophenol It dyes wool
and silk a fluorescent bluish red, and dyes tanned cotton
red.
XANTHENE DYESTUFFS 193
Violamines B, R, 2R, G are the hydrochlorides of the
phenyl- or tolyl-diamidofluoranes, obtained by the
action of aromatic amines, such as aniline, toluidine,
phenetidine, etc., on fluorescein chloride. Certain of
these dyestuffs are the sulphonic acids of such products.
Anisolines. The Anisolines are the esters of the
Rhodamines, just as the Erythrines are the esters of
the Eosines. In 1891, Momiet of Lyons (Bull. Soc. chim.,
1892, 523) obtained new dyestuffs, to which he gave
the name Anisolines, by treating the Rhodamine bases
with alkylogens. This nomenclature led to an erroneous
conception of the reaction, as it would appear that on
treating Rhodamines with alcoholic potash the pyrone
ring would be broken and the potassium salt of a di-
hydroxy-compound formed, which would be converted
by the alkylogen into a phenolic ester ; hence the name
Anisoline (from anisole) given to these compounds.
I \P TJ ^OK / |
^tt^ > \
,
C 6 H 4 a C C H 4
\l
CO
\J
CO
Bernthsen (Chem.-Ztg., 1892, 1956), of the Badische
Anilin und Sodafabrik, showed that Anisolines could be
obtained by heating Rhodamines with alcohol and a
mineral acid, and that the dyestuffs so obtained are
esters of the Rhodamines. There resulted the famous
lawsuit in London, in 1898 (Hon. sci., 1897, 1898 and
1899) between the Societ6 chimique des usines du Rhone
and the Badische Anilin und Sodafabrik, which ended
in the annulling of the two patents. That of Monnet,
of the Soci6te, was annulled because it claimed the
alkylation of a phenol which did not exist ; that of the
B.A.S.F. was annulled, due to the insufficient description
of the process, as experts found that the esterification of
194 ORGANIC DYESTUFFS
the Rhodaminc only proceeds satisfactorily in an iron
autoclave, being incomplete if the vessel is enamelled or
silvered.
The Anisolines are dyestuffs which are more basic than
the Rhodamines, and have the property of dyeing cotton
direct, but give much better results on tannin mordanted
cotton.
Rhodamine 3B or Anisoline is the ethyl ester of
Rhodamine B :
C 6 H 4 COOC 2 H 6
Rhodamine 6G is the most important of the Aniso-
lines, being the ethyl ester of the symmetrical diethyl
Rhodamine which results from the condensation of
phthalic anhydride with mono-ethyl-rft-amidophenol. It
dyes wool and silk a fluorescent red shade, and dyes
cotton direct, but better if mordanted with tannin.
Succineins. These dyestuffs are obtained by con-
densing succinic anhydride with dialkyl-m-amido-
phenols. Rhodamine S is the succinem of dimethyl -
ra-amido-phenol :
ci
\
C 2 H 4 COOH
In the same way saccharin (o-benzoic sulphinide)
vields Saccharems (Kotschet).
CHAPTER XVIII.
ACRIDINE DYESTUFFS.
The name hydroacridine has been given to the com-
pound obtained by tho loss of a molecule of ammonia
from a molecule of o-diamidodiphenylmethane by the
action of heat (I.) :
CH
NH
Nil.,
2 _
= NH a -f Clf
\
Nil
(I-)
(II.)
Hydroacridine (I.) and xanthene (II.) are very similar,
the oxygen atom in xanthene being replaced by the
divalent NH group to give hydroacridine, which on
oxidation yields acridine, a basic yellow substance which
forms fluorescent solutions ; its constitution has been
expressed by the formulae (I.) and (II.) :
196 ORGANIC DYESTUFFS
(II.)
Formula (II.), the ortJio-([uii\onoid structure, is the one
which agrees best with the present ideas of the con-
stitution of coloured substances. Acridine may be
considered as being derived from diphenylmethane ; but
there is also a phenylacridine (III.) which is related to
triphenylmethane. To obtain dyestuffs, auxochrornes
must be introduced into the molecule in para-position
to the carbon atom of the methane residue ; the only
dyestuffs of interest are those which contain amido- or
alkylamido-groups .
Preparation. The Acridine dyestuffs were discovered
by Benda in 1889. They are obtained by methods
similar to those used for xanthene derivatives. Formal-
dehyde is condensed with two molecules of a m-diamine
or of an asymmetrical dialkyl-m-diamine ; to obtain
triphenylmethane derivatives, the formaldehyde is
replaced by benzaldehyde.
+ H a
ACRIDINE DYESTUFFS 197
On heating the o-diamido derivative of diphenyl-
methan'e with an acid, it loses ammonia, yielding a
hydroacridine which on oxidation gives the dyestuff.
There are two methods of writing the formulae of
these dyestuff s, according to whether they are con-
sidered as para- or orJAo-quinonoid compounds :
NIL/
The similarity between the properties of the bases of the
dyestuffs and of acrid ine itself makes the or^o-quinonoid
formula 'the more probable. The commercial products
are the hydrochloridcs of these bases. Asymmetrical
acridines may be obtained by heating symmetrical
tetra mid o -derivatives of diphenylmethane with bases,
such as _p-toluidine, or phenols, such as /3-naphthol, a
molecule of a m-diamine being eliminated :
CH 3
This method may be modified by first acting on a
molecule of a m-diamine with a molecule of aldehyde,
198 ORGANIC DYESTUFPS
when an intermediate compound is formed, which in
the case of m-toluylenediamine appears to be
xNH
I /
*\
CH 2
On heating with amines or diamines, these inter-
mediate products give symmetrical or asymmetrical
Acridines.
Finally, Michler's ketone condenses with m-diamines
to give Auramines, which on heating are converted into
Acridines.
Acridine yellow is the hydrochloride of diamidodi-
methylacridine, and is obtained by condensing formalde-
hyde with m-toluylenediamine and oxidising with ferric
chloride the leuco -compound produced. It dyes tanned
cotton yellow.
Acridine orange, the hydrochloride of tetramethyl-
diamidoacridine, is obtained by condensing formaldehyde
with dimethyl-ra-phenylenediamine:
Benzoflavine, the hydrochloride of diamidodimethyl-
phenylacridine, is obtained by condensing benzaldehyde
with two. molecules of w-toluylenediarnine, and oxidising
the leuco-derivative obtained. It gives yellow shades
on wool, silk, and tanned cotton.
Chrysaniline. This is an asymmetrical isomeride of
Benzoflavine, and was discovered by Nicholson in 1863
among the secondary products from the manufacture
of Magenta by the arsenic acid method. Hofmann
determined its composition and formula as C 20 H 17 N 3 ,
and later Fischer and Korner (Ber., 1884, 17, 203) isolated
a second base, the lower homologue, C 10 H 15 N 3 , the
constitution of which was established by condensing
o-nitrobenzaldehyde with aniline, reducing the product,
and oxidising the jp-diamido-o-amidotriphenylmethane
obtained.
ACBIDINE DYESTUFFS 199
Its formation in the manufacture of Magenta may be
explained by supposing that on oxidation of a mixture
of >-toluidine and aniline, the methyl group of the
jp-toluidine condenses with two molecules of aniline,
combination occurring in the ^para-position with one and
in the or/7io-position with the other molecule. As the
yield is greater in presence of o-toluidine, the higher
homologue containing C 20 , which was the one analysed
by Hofmann, may be formed. The commercial product
is actually a mixture of the two dyestuffs, which, in the
form of their nitrates or hydrochlorides, form Phosphine,
which is used for dyeing leather and for printing cotton.
The Acridines give #lkylated derivatives of the type :
Cl R
Y
HAT r* TT ^y xr 1 TT TXJTT
2 L\ O 6 tl 3 X X> 6 tl 3 IN rlj
CH
These substances have been studied by Ullmann and
Naef (Ber., 1900, 33, 2470), and are strongly basic dye-
stuffs which have been called " acridinium " compounds.
CHAPTER XIX.
ANTHRACENE DYESTUFFS.
Anthracene is a colourless hydrocarbon which yields
a diketone, anthraquinone, on oxidising with chromic
acid :
CH CO
C 6 H 4 | C 6 H 4 +30 = H 2 + C 6 H 4 .H,
\ / \ /
CH CO
Anthraquinone is of a pale yellow colour, and is one
of the most important chromogens. To obtain dyestuffs,
it is only necessary to introduce OH, NH 2 , NR 2 , e ^ c -?
groups in suitable positions.
Buntrock (Ber., 1901, 34, 2344) has proposed that the
Anthraquinone dyestuffs should be divided into three
classes :
(1) Those which only contain OH auxochromes,
which only have pronounced tinctorial properties if
they contain the two OH groups in or^o-position ;
these dyestuffs only dye on mordants.
(2) Those containing both OH and NH 2 , or NR 2 ,
groups, which dye both on mordanted and unmordaiited
animal fibres, and in which the OH group need not be in
ortho-position.
(3) Those which only contain NH 2 or NR 2 auxo-
chromes and do not, dye on mordants.
The dyestuffs derived from anthracene will here be
discussed in the following order :
I. The hydro xy-dyestuffs, or oxyanthraquinones.
ANTHRACENE DYESTUFFS 201
II. The amido-dyestuffs, or amidoanthraquinones, and
their derivatives.
III. The dyestuffs which contain a further chromogen
other than anthraquinone.
I. Oxyanthraquinones.
The hydroxy-derivatives of anthraquinone dissolve in
alkalies to form violet or blue solutions. Their use
in dyeing depends on their property of forming insoluble
lakes with metallic hydroxides. This property is not,
however, common to all the oxyanthraquinones. Of the
two isomeric mono-oxyanthraquinones, the one in which
the OH group is near to the chromophore (CO) has to
some extent the property of dyeing on metallic mordants.
The introduction of a second OH group in or/Ao-position
to the first one increases the affinity for mordants, this
affinity being greatest when, the two OH groups being
in or^o-position to one another, one of them is near to
the chromophore (CO). This is the case in Alizarin,
1 : 2-dioxyanthraquinone (the carbon atoms of anthra-
cene are numbered from 1 to 10 as shown) :
At one time it was considered possible to generalise
by stating that, for a polyoxyaiithraquiiione to be a
useful mordant dyestuff, it must contain at least two
OH groups in or^o-position, of which one should be
adjacent to the CO group, this being known as the rule
of Liebermann and Kostanccki. It has since been
recognised that this is somewhat too general, as anthra-
quinone derivatives are now known which are mordant
202 . ORGANIC DYESTUFFS
dyestuffs, but do not fulfil these conditions. Thus by
introducing a hydroxyl group and a carboxyl, nitroso,
quinone, or oxime group, or two oxime groups, in ortho-
position into a chromogen, the resulting compound is
a pronounced mordant dyestuff. Nolting has also
shown (Chem.-Ztg., 1910, 977) that the introduction of
a hydroxy- and an amido-group in oriho- or para-
position has the same effect (see p. 218) ; this is pro-
nounced in the case of the Anthraquinone series, but is
not so evident in the other series.
The rule of Liebermann and Kostanecki shows that,
of the tri-, tetra-, or poly-oxyanthraquinones, the only
ones of practical interest are the oxyalizarins, the
mono-oxyanthraquinones being of no interest in dyeing.
Dioxyanthraq uinones .
All the ten dioxyanthraquinones predicted by theory
have been prepared ; they have the following names :
1 : 2 dioxyanthraquinonc Alizarin.
1:3 ,, ,, Purpuroxanthin.
1:4 ,, ,, Quinizarin.
1:5 ,, ,, Anthrarufin.
1:6 Recently prepared by Fro-
benius and Hepp (Ber.,
1907, 40, 1048).
1:7 ,, m-Dioxyanthraquinone.
1:8 ,, * ,, Chrysazin.
2:8 ,, ,, Histazarin.
2:6 ,, ,, Anthraflavic acid.
2:7 ,, ,, Isoanthraflavic acid.
Of these, the most important are : Alizarin, which
is itself a dyestuff, and the three clioxyanthraquinones
which have the OH groups near to the chromophore :
Quinizarin, Anthrarufin, and Chrysazin, which are used
for the preparation of other dyes tuffs.
ANTHRACENE DYESTUFFS 203
Alizarin is a dyestuff which is present in the roots
of plants of the madder-family, mainly in the rubia
tinctorum L or madder, in which it occurs as the glucoside,
ruberythric acid, together with the trioxyanthraquinone
Pur pur in.
According to Pliny, madder was used in the ancient
civilisations. During the reign of Charlemagne, the
cultivation of the madder was much encouraged, but it
disappeared completely in the following years. It was
taken up again in the sixteenth century in Holland and
in Saxony about the year 1507, and again in France
in 1729, where it was mainly carried on in Alsace, and
then under Louis XVI. in Provence. With the Revolu-
tion and the Empire, the use of madder gradually
decreased until the time of Louis-Philippe, when its
culture was increased in consequence of its use for
dyeing military materials. This prosperity continued
until the synthetic manufacture of Alizarin completely
replaced the cultivation of the madder plant. Although
it is still used for dyeing military materials, synthetic
Alizarin has almost entirely replaced the natural product.
Constitution of Alizarin. Alizarin and Purpurin were
first extracted from madder-root by Robiquet and
Colin in 1826. The constitution and even the exact
composition of these products remained unknown for a
very long time. This was partly due to the difficulty
of obtaining them in the pure state, and partly to the
inexact atomic weights which were then known. It w r as
for these reasons that Robiquet, who published exact
204 ORGANIC DYESTUFPS
analyses of Alizarin in 1835, having found : C, 70-09 per
cent. ; H, 3-73 per cent. ; (theoretical for C 14 H 8 4 : C, 70-00
per cent., H, 3-33 per cent.}, deduced an incorrect formula,
CgfH^Ojo, which corresponds to C 37 H 48 10 with the
present atomic weights. Other formulae proposed were :
C 20 H 18 9 (Schiel), C 30 H 20 O 9 (Debus), C 14 H 10 O 4 (Schunck
in 1848). From this time confusion was caused by the
fact that Schunck obtained by the oxidation of Alizarin
an acid which he called alizaric acid, and which Gerhardt
in 1849 considered to be identical with phthalic acid,
which Laurent had obtained by oxidising naphthalene.
This view was confirmed by Wolff and Strecker in 1850,
and from that time Alizarin was considered to be a
derivative of naphthalene, the formula C 10 H 6 3 being
assigned to it until 1868. These ideas led Roussin to the
discovery of Naphthazarin, in 1861, by heating I :5
and 1 : 8 dinitronaphthalene with sulphuric acid and
zinc, the mechanism of the reaction being explained
later by Zincke and Schmidt (Ann., 1895, 286, 27). This
substance is a 1 : 2 dioxynaphthaquinone of the following
formula :
o
ii OH
At about the same time that Roussin discovered
Naphthazarin, Graebe and Liebermann were studying
the quinones and their hydroxy-derivatives ; they
found a great similarity between these compounds
and Alizarin and Purpurin. By applying to the latter
compounds the method of distilling with zinc powder,
which gives the hydrocarbon, a method which Baeyer
had just used with success in other cases, Graebe and
Liebermann* (Ber., 1868, 1, 49) obtained anthracene.
ANTHRACENE DYESTUFFS
205
Alizarin and Purpurin were hence derivatives of
anthracene, probably being dioxy- and trioxy-anthra-
quinones :
C 14 H 6 (OH) 2 { > and C 14 H 5 (OH) 3 { >
This deduction received a striking confirmation by
the synthesis of Alizarin, carried out by Graebe and
Liebermann on January llth, 1869, by heating di-
bromoanthraquinone with caustic potash. This was the
first synthesis of a naturally occurring dyestuff. De
Lalande having shown that the oxidation of Alizarin
gives Purpurin and then phthalic acid, it followed that
the hydroxyl groups must be present in only one of
the rings of anthraquinone, which according to Ziiicke
and Fittig has a symmetrical constitution, and their
constitutions become :
CO
4 /' \
X CO
Alizarin.
CO
\C 6 H(OH) 3
2 and C 6 H 4 63
CO
Purpurin.
The positions of the OH groups were determined by
Baeyer and Caro (1874-5), as follows : the condensation
of phthalic anhydride with pyrocatechol in presence of
sulphuric acid yields Alizarin, and hence the two
hydroxyl groups are in or^o-position to one another.
Two formulae are then possible :
CO OH
CO
OH
CO
,OH
'OH
(ii.)
On the other hand, if hydroquinone is condensed
with phthalic anhydride under the same conditions, an
206 ORGANIC DYESTUFFS
isomer of Alizarin is obtained, Quinizarin, in which the
hydroxyl groups must be in ^ara-positioii to one another ;
co on
co OH co on
Quinizarin. Purpurin.
Careful oxidation of Quinizarin gives Purpurin,
which must therefore be 1:2:4 trioxyanthraquinone.
As Alizarin also gives Purpurin on oxidation, it must
have in it two OH groups in 1 : 2 positions and not 2:3.
Hence Alizarin is 1 : 2 dioxyanthraquinone and has
formula (I.) on p. 205.
Manufacture of Alizarin. The commercial applica-
tion of Graebe and Liebermann's synthesis encountered
great practical difficulties ; at that time anthracene was
still a rare product, and its conversion into dibromo-
anthraquinone was expensive. Caro, at the Badische
Anilin und Sodafabrik (who used the method), found
that anthraquinone may be converted under certain
conditions into the sulphonic acid and this latter into
Alizarin. This discovery was patented in England on
the 25th of June, 1869. On the following day, Perkin
applied for a provisional patent for an identical process
which he had discovered independently. The two in-
vestigators then collaborated with the B.A.S.F.
The commercial manufacture includes three processes :
oxidation of the anthracene to anthraquinone, sul-
phonation of this product, and then alkaline fusion of
the sulphonic acid. The anthraquinone is prepared
by oxidising anthracene with potassium or sodium
dichromate and sulphuric acid. After being purified
as already described (p. 17), the anthracene must be
sublimed. This is carried out by heating in a hori-
zontal vessel connected with a condensing apparatus,
ANTHRACENE DYESTUFFS 207
the anthracene vapours being carried forward by a
current of superheated steam at 220-240. The con-
densation is effected in an apparatus in which is a
spray of water which precipitates the anthracene in
small crystals. These are dried and then sieved to
separate the fused particles which are rich in phen-
anthrene. The anthracene content of this product is
determined and the amount of oxidising agent necessary
is calculated . The dilute solution of sodium or potassium
dichromate (100 to 150 kilograms in 1,500 litres of water)
is placed in a lead-lined wooden vat fitted with a stirrer,
and brought to the boil by passing in steam. 100
kilograms of the finely divided anthracene is then added,
and the corresponding amount of dilute sulphuric acid
(52 Tw.) then run in slowly over a period of nine to ten
hours. The heat evolved by the reaction keeps the mass
at the boil, and when all the acid has been added it is
kept boiling for a short time and then allowed to cool.
The crude anthraquinone which is precipitated, is
separated by a filter press, washed, and then purified.
For this purpose it is dried, two to three parts of
sulphuric acid (168 Tw.) added, and the whole heated
in a cast-iron vessel to 80 until the anthraquinone is
completely dissolved. The liquid is then heated to
110 until a sample poured into water gives a pure white
precipitate. All the impurities will then have been
converted into sulphonic acids, the anthraquinone being
unchanged. The liquid is allowed to cool, and then
poured into twenty times its weight of water, the resulting
liquid boiled and the anthraquinone separated and dried.
It will then contain about 90 per cent, of anthraquinone,
and may be further purified to a 98 per cent, content
by boiling with a solution of sodium carbonate, and
subliming. The yield is 96-98 per cent, of the
theoretical.
Sulphonation of Anthraquinone. On heating anthra-
quinone to a high temperature (250-260) with con-
centrated sulphuric acid, a mixture of the mono- and
208 ORGANIC DYESTUFFS
di-sulphonic acids is produced. Since the commencement
of the manufacture of artificial Alizarin in 1871, it has
been noticed that in order to obtain a bluish shade of
Alizarin it is necessary to commence with the inono-
sulphonic acid, whereas the use of anthraquinone di-
sulphonic acid yields a yellowish Alizarin, which contains
trioxyanthraquinone, and is of less value. Sulphonation
with ordinary acid was then replaced by sulphonation
with fuming sulphuric acid, which permits of the process
being carried out at a lower temperature. The following
conditions are those which obtain in practice : one part
of 95 per cent, anthraquinone is heated with one part of
fuming sulphuric acid (containing 45 per cent, of S0 3 )
for one hour at 160-170, and then the mass is allowed
to run in a thin stream into boiling water. Under
these conditions about 20-25 per cent, of the anthra-
quinone remains unchanged, and, as it is insoluble,
may be separated by filtration, leaving a solution
containing a mixture of the mono- and di-sulphonic
acids. The solution is neutralised by means of caustic
soda, and, on cooling, the hydrated sodium salt of
anthraquinone /3-monosulphonic acid is precipitated in
glistening plates known as " silver salt."
O 3 Na
+ H 2
CO
On concentration the mother liquors yield a further
amount of a less pure sample of the salt, but if the con-
centration is carried further sodium sulphate separates ;
finally, by evaporating to dryness the solution freed
from this salt, a mixture of the sodium salts of the a- and
/3-disulphonic acids is obtained. These disulphonic acids
are obtained free from the mono-acid by sulphonating
anthraquinone with two or three parts of the fuming
acid until all the anthraquinone has been converted.
ANTHRACENE DYESTUFFS 209
Alkaline Fusion of " Silver Salt." The sodium salt
of anthraquinone monosulphonic acid yields Alizarin
on fusing with caustic potash or caustic soda. In the
same way the anthraquinone disulphonic acids yield
trioxyanthraquinones (Purpurin, etc.). The number of
hydroxy -groups which may be introduced in this manner
is equal to the number of sulphonic acid groups plus
1, whereas in the case of the benzene and naphthalene
sulphonic acids, alkaline fusion replaces the sulphonic
acid groups by an equal number of hydro xy-groups.
This further hydroxy-group is produced by oxidation :
C 14 H 7 2 SO 3 Na + 3NaOH + O 2
" Silver salt."
= C 14 H 6 O 2 (ONa) 2 + Na 2 S0 4 + 2H 2 O.
Sodium salt of Alizarin.
This fusion was originally carried out in shallow cast-
iron vessels with a large surface, fitted with a mechanical
stirrer, and heated to 200-280. Under these conditions
an oxidation occurs partly by the oxygen of the air
and partly at the expense of the organic material itself.
To avoid the latter, which results in a smaller yield,
Koch has recommended (he addition of sodium chlorate
to the melt. The process is very long, lasting several
days, and only gives a yield of 30-40 per cent, of the
theoretical. This process has hence been modified : the
mixture of u silver salt " and alkali is first melted in
iron vessels and the mass spread out in a thin layer
oh iron plates heated in oil stoves. The air passing
over the plates oxidises the mass completely, and the
yield is raised to 80 per cent, of the theoretical. Since
the year 1873, the kt silver salt " has been heated under
pressure with caustic soda solution ; as the reaction
takes place in a closed vessel, potassium chlorate is
added to yield the necessary oxygen. The operation
is carried out in wrought-iron vessels furnished with
O.D. . O
210 ORGANIC DYESTUFFS
stirrers, and capable of withstanding great pressure,
The temperature attained is 160, and the reaction lasts
for twenty hours (for details, see Diet, de Wiirtz, Suppl. :
p. 100, and A. G. Perkin (Mon. sci. 9 1897, 498) ). The
mass i& poured into water and the boiling liquid neutra-
lised by hydrochloric acid or dilute sulphuric acid,
Alizarin is precipitated, and is separated and washed,
It comes into the market in the form of a 20 per cent,
paste, or for export in 40 to 60 per cent, pastes to
reduce the cost of transport.
Properties. Alizarin is almost insoluble in cold water ;
it crystallises from dilute alcohol in yellow plates ol
M.P. 289-290. It is used in dyeing and printing to
obtain shades which are fast to washing and to light,
When used on mordanted material, it gives the follow-
ing shades : With aluminium hydroxide, bluish red ;
with chromium hydroxide, reddish brown ; with ferric
hydroxide, deep violet ; and with stannic hydroxide,
violet. Liechti and Suida, Liebermann, Guggiari (Ber.,
1912, 45, 2442) and others, have shown that the composi-
tion of these lakes approaches those of the normal salts,
On the other hand, Biltz, Haller (Farb.-Ztg., 1912, 489,
523) and others, are of the opinion that lake-formation
is a phenomenon of a colloidal character.
According to the purity of the Alizarin, the red
obtained with alumina is more or less yellow ; the
production of blue shades of Alizarin is due to the use
of pure Alizarin or admixture with a little Purpurin :
yellowish shades of Alizarin consist mainly of Isopur-
purin and Flavopurpurin.
The leuco-compounds of Alizarin and of its derivatives
which only contain one oxygen atom in the nucleus, for
example :
C 6 Hc c H 2 (OH) 2
CH
are mordant dyestuffs, which give fast shades with wooj
ANTHRACENE DYESTUFFS 211
and cotton on chrome mordant, and on wool by the
after-chrome method (Bayer Co., E.P. 27,028 (1909)).
On treatment with fuming sulphuric acid at 140,
Alizarin gives a sulphonic acid, the sodium salt of which
forms Alizarin S, used for dyeing wool on alumina or
chrome mordant.
There should exist 6 nitroalizarins, of which three
are known ; the most important are - and /3-nitro-
alizarin :
CO OH CO OH
CO NO 2
a-Nitroalizarin is obtained by nitrating diacetyl-
alizarin or benzoylalizarin, or by nitrating Alizarin itself
in sulphuric acid solution. It crystallises in needles
of M.P. 194-196.
(3-Nitroalizarin is the most important. It is prepared
by treating solid Alizarin with nitrous fumes, or by
passing these fumes into a solution of Alizarin in nitro-
benzene, petroleum ether, ether, etc. Alizarin may
also be nitrated in glacial acetic acid solution (Rosen -
stiehl, Compt. rend., 1876, 82, 1455 ; 83, 73 ; Schunck
and Romer, Ber., 1879, 12, 581). /3-Nitroalizarin forms
orange needles of M.P. 244. It comes on the market
in the form of a 20 per cent., paste under the name of
Alizarin orange, and is used on alumina or chrome
mordant, with which it gives orange and bro\\n shades
respectively. It is also used for the manufacture of
Alizarin bhte.
homers of Alizarin.
Qiiinizarin, or 1 : 4 dioxyanthraquinone, is obtained
by condensing phthalic anhydride with hydroquinone by
means of sulphuric acid, or by heating anthraquinone
212 ORGANIC DYESTUFFS
with concentrated sulphuric acid in presence of boric
acid or sodium nitrite. It crystallises from alcohol in
red needles.
Antfirarufin, or 1 : 5 dioxyanthraquinone, is obtained
by condensing two molecules of m-oxybenzoio acid in
sulphuric acid solution, or by treating anthraquinone
or erythroanthraquinone with fuming sulphuric acid,
containing 75-95 per cent. SO 3 , in presence of boric acid.
Finally, it may be obtained by heating anthraquinone
1 : 5-disulphonic acid with milk of lime under pressure
(Hochst Farbwerke, D.R.P. 106,505).
Chrysazin, or 1 : 8-dioxyanthraquinone, is prepared
by heating the corresponding 1 : 8-disulphonic acid
under pressure with lime.
Trioxyanthraquinones.
The most important trioxyanthraquinones are those
which have two hydro xyl -groups in or/Ao-position to
one another, one being adjacent to the CO, that is to say,
the oxvalizarins, of which there are six :
Anthragallol, 1
Purpurin, 1
Oxyanthrarufin, 1
Flavopurpurin, 1
Isopurpurin, 1
Oxychrysazin, 1
3-trioxyanthraquinone.
4-
6-
7-
8-
Anthragallol is obtained by condensing benzoic acid
and gallic acid in molecular proportions in sulphuric
acid solution. Anthragaliol is present together with
rufigallic acid in Anthracene brown, which gives brown
shades on alumina or chrome mordant.
Purpurin was found to be present with Alizarin in
the madder-root in 1826. Lalande prepared it syn-
thetically by oxidising Alizarin with arsenic acid, or
with manganese dioxide and sulphuric acid. It forms
ANTHRACENE DYESTUFFS 213
orange needles of M.P. 253. Purpurin dissolves in a
boiling solution of alum, forming a yellowish red fluores-
cent liquid. By this reaction, natural Alizarin extracted
from madder, which contains Purpurin, may be dis-
tinguished from synthetic Alizarin. Purpurin gives
scarlet shades on alumina mordant.
Oxyanthrarufin is obtained by the action of fuming
sulphuric acid on Alizarin in presence of boric acid.
Flavopurpurin is prepared by the alkaline fusion of
anthraquinone disulphonic acid in a closed vessel in
presence of potassium chlorate. It is commercial in the
form of a 20 per cent, paste, and gives a yellowish red
shade on alumina mordant and a violet red on iron
mordant ; it is called Alizarin {?/, EG, SDG, X, etc.
Lsopurpurin is obtained by the alkaline fusion of
anthraquinone-2 : 7-disulphonic acid. It is also called
Anthrapurpurin, or oxyisoanthraflavic acid, and gives
scarlet shades on alumina mordant.
Polyoxyanthraquinon^s .
The polyoxyanthraquinones are obtained by oxidising
the di- or tri-oxyanthraquinones. This oxidation may
be carried out by means of manganese dioxide in sul-
phuric acid solution, or by sulphuric anhydride. The
latter process has become of considerable importance,
tetra- and penta-oxyanthraquinones, etc., being readily
obtained by its use. The oxidising action of S0 3 had
already been employed by Bohn (Ber., 1890, 23, 3739)
in the case of Alizarin blue, and was extended by Graebe
and Phillips (Ann., 1893, 276, 21), and Gattermann and
Schmidt (J. prakt. Cliem^ 1891, 43, 237, 246 ; 1892, 44,
103) to the hydroxy-derivatives. This oxidation with
fuming sulphuric acid commences even at 50, whereas
ordinary sulphuric acid requires higher temperatures
(200), at which secondary reactions occur. By this
process two hydroxyl groups can generally be intro-
duced in para-position to one another. The oxidising
214 ORGANIC DYESTUFFS
action of sulphuric anhydride may be represented by
the following equation :
but actually the reaction is more complicated ; neutral
sulphuric esters are formed which are converted by the
action of alkalies and acids into acid esters and then into
diphenols :
OH OH
It has further been found that the presence of boric
acid aids this reaction considerably, and it may then be
effected even by means of concentrated sulphuric acid.
By this last process, anthraquinone may be converted
directly into Quinizarin.
Alizarin bordeaux, or 1:2:5: 8-tctraoxyanthra-
quinone, is obtained by heating Alizarin with fuming
sulphuric acid containing 70 per cent, of S0 3 , and then
saponifying the sulphuric ester formed :
OH
OH
It dyes wool mordanted with alumina a claret shade,
and gives dark violet shades on chrome mordanted wool.
Alizarin Viridine DO or FF [By.] is obtained by
heating Alizarin bordeaux with jp-toluidine and aul-
phonating the product ; it has the following constitution :
ANTHRACENE DYESTUFFS 215
CH q
)H
In presence of a large excess of chromium acetate,
green shades are obtained which are exceedingly fast to
washing (Hannay, Journ. Soc. Dyers and Col., 1913, 36).
Alizarin Cyanine, 1:2:4:5: 8-pentaoxyanthraquinone,
is related to Alizarin bordeaux in the same manner that
Purpurin is related to Alizarin. It is obtained by
oxidising this dyestuff with manganese dioxide and
sulphuric acid. It dyes wool mordanted with alumina
a blue shade.
The other pentaoxyanthraquinones are prepared by
oxidising trioxyanthraquinones with S0 3 .
Rufigallic acid, 1 : 2 ; 3 : 5 : 6 : 7-hexaoxyanthra-
quinone, was obtained by Robiquet in 1836 by heating
gallic acid with sulphuric acid. It gives brown shades
on chrome mordanted material.
Anthracene blue, 1:3:4:5:7: 8-hexaoxyanthra-
quinone, is obtained by heating 1 : 5-dinitroanthra-
quindlie with fuming sulphuric acid, containing 40 per
cent, of SO 3 , with or without a reducing agent. Sulphuric
esters are first formed and are then hydrolysed. It is
commercial in the form of a paste, and dyes chrome
mordanted material blue. Its sulphonic acids form the
Alizarin Acid blues BB and GR [M.L.B.].
Octaoxyanthraquinone has recently been prepared by
Georgievics (Monatsh.f. Chem., 1911, 32, 347) by oxidis-
ing Rufigallol with sulphuric acid in presence of boric
acid and mercury.
II Amido- and Hydroxyamido-Dyestuffs,
If polyoxyanthraquinones are heated with ammonia
under pressure, new dyestuffs are obtained in which a
216 ORGANIC DYESTUFFS
certain number of the NH 2 groups are substituted for
hydroxyl groups. The amido- and alkyl- or aryl-amido-
derivatives of anthraquinone are very valuable dye-
stuffs, being used in the form of their sulphonie acids.
These dyestuffs generally have the amido-groups in
a-position, that is, adjacent to the ketonic group. Their
sulphonie acids are acid dyestuffs for wool which dy6
from an acid bath ; they yield very bright shades, similar
to those of the tripheriylmethane dyestuffs, but differing
from these in their great fastness to light, a property
which is characteristic of the anthracene derivatives.
Amidoanthraquinone and its Derivatives.
The most important of these dyestuffs are those which
contain one or two NHR groups, where R represents
a sulphonated aromatic nucleus. They are obtained
by heating disubstituted derivatives of anthraquinone
with aromatic amines ; these derivatives may be
dibrom-, dichlor-, dinitro- or dihydroxy-anthraquinones,
or anthraquinone disulphonic acids, or their reduction
products, or mixed derivatives such as the bromonitro-,
hydroxynitro-, etc., compounds. Thus on boiling
Quinizarin or leuco-Quiriizarin with ?>-toluidme, with
or without the addition of boric acid, the following
reaction occurs :
CO OH
+ 2NH 8 CH 4 OH 3
\/
CO OH
CO NH C 6 H 4 CH 3
ANTHRACENE DYESTUFFS 217
In order to render this product soluble, it is sul-
phonated, when the sulphonic acid groups enter the
toluidine nucleus, giving Alizarin Cyanine green.
By using a 1 : 5-disubstituted anthraquinone, the
isoiner, Anthraquinone violet, is produced :
CO
SO 3 H
The reaction may also be made to take place in such
a manner as to introduce two different amine residues
in turn ; thus one may be aromatic, the other aliphatic.
as in Alizarin Astrol :
CO NH C
MI CH 3
The constitution of these dyes tuffs has been established
by Friedliinder and Schick (Zeitsch. Farben- u. Tcxtil-
Chemie, 1902, 2, 429 ; 1903, 3, 218).
Hydroxyamidoanthraquinones and their Derivatives.
These compounds may be obtained in several ways :
by heating hydroxyanthraquinories with ammonia under
pressure ; by partial reduction of the nitro-derivatives ;
or by carefully heating aromatic amines with a-hydroxy-
derivatives of anthraquinone. Again in this case the
sulphonic acids are used as acid dyestuffs for wool.
The oldest dyestuff known of this series is Alizarin
Saphirol, which may be obtained either from Anthrarufin,
218
ORGANIC DYESTUFtfS
by sulphonating, nitrating, and then reducing, ot
from 1 : 5-dinitroanthraquinone, by reducing carefully
in alkaline solution, acidifying, and sulphonating the
product. It has the following constitution :
on co NH 2
S0 3 H,
NH 2 CO OH
By the action of formaldehyde, Alizarin CeUsiol is
obtained.
If, in the preparation of Alizarin Cyanino green, only
one group is replaced by ytoluidine, there is obtained
the arylainido-hydroxy-dyestuff, Alizarin Irisol :
co
CTT
CO NH-0 6 H,< SO H
Certain of these 2>-hydroxyamido-dyestuffs also dye
on metallic mordants (Nolting, Mon. sci., 1911, 540 ;
Fdrb.-Ztg., 1911, 22, 174). Thus thj Bayer Co. dis-
covered that dinitrochrysazin :
OH
OH
NO.,
gives blue shades on chrome mordanted wool, and it has
since been shown that it also dyes on mordanted cotton ;
diamidochrysazin possesses the same properties.
The hydro xyamido -derivatives give full shades on
copper mordant (Nolting, Chem.-Ztg. 9 1910, 977).
ANTHRACENE DYESTUFFS 219
III Anthraquinone Derivatives containing a
Further Grouping.
By treating /3-nitroalizarin with glycerol and sul-
phuric acid, Pnidhomme (Bull. Soc. ind. de Mulhouse,
1877, 28, 62) obtained a substance which crystallised in
blue needles, dyed chrome mordanted wool, and which
he called Alizarin blue. Graebe (Ber., 1878, 11, 522,
1646 ; 1879, 12, 1416 ; and 1882, 15, 1783) determined
its constitution, and showed that it is formed according
to the following equation :
C 14 H 7 (N0 2 )0 4 + C 3 H 8 3 = C 17 H 9 N0 4 + 3H 2 0+0 2 .
The oxygen liberated causes the formation of brown
secondary products. Alizarin blue is also obtained by
heating /3-amidoalizarin with glycerine, sulphuric acid,
and nitrobenzene. In these reactions the glycerine yields
acrolein, which condenses with the Alizarin derivative,
giving a dioxyanthraquinolinequinone :
CO OH CO
= lillgO +
This is identical with the reaction which is used for
the synthesis of quinoline from aniline, glycerine, and
sulphuric acid (Skraup's reaction).
Alizarin blue is more often found in commerce in
combination with sodium bisulphite as Alizarin blue S,
which is used for printing chrome mordanted cotton.
If the jS-nitroalizarin is replaced by its a-isomer, a
green dyestuff is obtained, Alizarin green S [M.L.B.],
which is used on nickel mordant.
220 ORGANIC DYESTUFFS
In 1890 R. Bohn found that on treating Alizarin blue
with fuming sulphuric acid containing 70 per cent,
of anhydride, there were formed successively several
products. Alizarin blue-green, which is the sulphonic
acid of a trioxyanthraquinolinequinone, is first produced,
and then this compound is converted by treatment with
concentrated sulphuric acid at 120 into tetrao*xy ant lira -
quinolinequinone, the bisulphite compound of which is
Alizarin green S [B.A.S.F.] :
OH SO 3 Na
\/
OH C OH
,OH
By raising the temperature to 200, another hydroxyl
group is introduced, giving Alizarin indigo blue.
Vat Dyestuffs derived from Anthracene.
The name " vat-dyestuffs " has been given to those
dyestuffs which are* insoluble in water, but give soluble
products on reduction, which may be coloured or other-
wise, and which have a distinct affinity for textile
fibres. For dyeing it is sufficient to allow the material
to remain in the vat, remove it, and expose to air ;
the original insoluble substance is again formed inside
the cells of the fibre, on which it is thus fixed. Indigo
is a typical vat-dyestuff, and fora long lime the vat-
dyestuffs were limited to Indigo, its derivatives, and the
Indophenols. Some twelve years ago it was found that
certain compounds derived from anthracene also had
the property of dyeing vegetable fibres from a vat. The
ANTHRACENE DYESTUFFS
221
number and variety of these new dyestuffs has increased
in a remarkable manner since 1901, and their commercial
importance is now very considerable.
Anthraquinone itself dissolves in alkaline reducing
agents to give oxanthranol,
HC(OH)
CO
which is soluble in alkalies, forming blood-red solutions
which oxidise even on exposure to air, regenerating
anthraquinone. The tinctorial properties of anthra-
quinone and its simple derivatives are not, as a rule,
sufficiently pronounced to allow of their use as vat
dyestuffs. For these it is generally necessary to obtain
more complex compounds of much higher molecular
weight, containing, in addition to the ketone groups of
anthraquinone, nitrogen, sulphur, etc., groups. These
products may be divided into several classes. Thus
Bohii divides them into Indanthrene, Flavanthrene,
Bcnzanthrone, anthraquinoneimides and acylamidoan
thraquinones.
Indanthrene.
This was the first of the anthracene vat dyestuffs
known. It was discovered by R. Bohn at the Badische
Anilin und Sodafabrik in 1901 by heating /3-amidoaiithra-
quinone with caustic potash at 200-300 (B.A.S.F.,
D.K.P. 129,845 to 129,848 (1901) ). The mass is dis-
solved in boiling water, and deposits the dyestuff in the
crystalline form if the liquid is agitated 'by a current of
air. The reaction has been studied by R. Scholl (Ber.,
1903, 36, 3410, 3710), Scholl and Berblinger (Ibid., 3427),
Scholl, Berblinger and Mansfeld (Ber., 1907, 40, 320,326),
222
ORGANIC DYESTUFFS
Scholl, Steinkopf and Kabacznik (Ibid., 390), Scholl and
Berblinger (Ibid., 395), Scholl and Stogmiillor (Ibid., 924),
and Scholl (Bcr., 1907, 40, 933 ; 1908, 41, 2320), and has
been found to result from the condensation of amido-
anthraquinone with liberation of hydrogen :
2C 14 H 9 2 N = C 28 H 14 4 N 2
It has been stated that Alizarin is obtained as a
bye-product.
Scholl has shown that Indanthrene blue US is
1:2:1': 2 / -aiithraquinoneazine ;
2H 2 .
The B.A.S.F. have now adopted "Indanthrene " as
a trade description of all their anthraquinone vat
colours.
The action of alkaline reducing agents on Indanthrene
gives a blue substance, which dyes vegetable fibres blue
shades which are extremely fast to light and washing,
but are not resistant to chloiine, such compounds being
obtained by introducing halogens into the dyestuff ; for
example, the monobromo-derivative Indanthrene blue
RC y and the dibromo-derivative Indanthrene blue OC
(E.P., 4035 (1912) ), and the chloro-derivatives Ind-
anthrene blue GOD (dichloro-indanthrene, E.P. 23,179
(1903) ), and CE (D.R.P. 168,042), and Algol blue OF.
Algol blue 3G is a dihydroxy-indanthreno, and gives
ANTHRACENE DYESTUFFS 223
bright greenish blue shades (D.R.P. 193,121). Ind-
anthrene blue 3(? and 2GS (D.R.P. 227,790) are probably
hydroxy-indanthrenes, the former giving bright greenish
blus shades, and the latter ultramarine shades. Algol
blue K is N-dimethyl-indanthrene (D.R.P. 158,287),
and is fairly fast. Algol green B is dibromodiamido-
indanthrene (D.R.P. 193,121) ; it is fast except to
bleaching.
Indanthrene grey B (E.P. 712 (1904) ) is obtained by
the alkaline fusion of 1 : 5-diamidoanthraquinone, and
is exceedingly fast to light and washing. By alkaline
fusion of the formaldehyde compound of the above
diamine, there is produced Indanthrene maroon, which
yields brown shades, fast to light and washing.
When the azine constitution of Indanthrene had been
established, the various methods for the synthesis of
the azines (see p. 258) were applied to the anthracene
series. Thus the Bayer Co. (D.R.P. 178,130) have
obtained a compound isomeric with Indanthrene by
condensing Alizarin with o-diamidoanthraquinoiie.
224 ORGANIC DYESTUFFS
The reaction which occurs on. the alkaline fusion of
/3-amidoanthraquinone being one of oxidation, attempts
were made to carry out the oxidation in aqueous solution.
/3-Amidoanthraquinone actually gives a mixture of
Indanthrene and Flavanthrene (see later) on oxidising
with chromic acid, lead dioxide or nitric acid.
If instead of oxidising an amido-derivative, a methyl-
anthraquinone, such as 2-methylanthraquinone, is
oxidised in acid solution by means of lead dioxide, a
dyestuff is obtained which, in place of the two NH
groups of Indanthrene, contains methylene groups :
CO
CO
This compound is known as Anthraflavone, and is a
yellow dyestuff which is not very fast to light.
Flavanthrene.
Flavanthrene is formed together with Indanthrene
by the alkaline fusion of /3-amidoanthraquinone on
raising the temperature to 300. With hydrosulphite
this dyestuff gives a blue compound, which oxidises in
air to give Flavanthrene, which is yellow ; the product
obtained by the action of zinc powder and an alkali is
brown. The blue compound is dihydroflavanthrene,
whereas the brown compound is the tetrahydro-deriva-
tive. Both yield Flavanthrene on oxidation.
The constitution of Flavanthrene has been established
ANTHRACENE DYESTUFFS
225
by R. Scholl, the reaction which occurs on alkaline fusion
resulting in the elimination of water, as follows :
2C 14 H 9 O 2 N = C 28 H 12 O 2 N 2 + 2H 2 + H 2 .
It would appear probable that this is due to the
condensation of amido-groups with ketonic groups :
CO
CO
= :JH,>O -f Ho
In order to prove this formula, Scholl has synthesised
Flavanthrene as follows : /3-methylaiithracene is con-
verted by oxidation into j8-methylanthraquinone, which
is nitrated, the product being reduced, the arnido-com-
pound diazotised, and the diazo-compound decomposed
by means of cuprous chloride. The chloro-derivative so
obtained is treated with powdered copper, when it loses
its chlorine and gives 2 : 2'-dirnethyldiaiithraquinonyl
CO
CO
O.D.
226
ORGANIC DYESTUFFS
On oxidising, the methyl groups of this compound arc
converted into carboxyl groups, and the product so
obtained, on treatment with phosphorus pentachloride,
ammonia, and then sodium hypobromite, yields
diamidodianthraquinonyl, which is easily converted into
Flavanthrene by dehydrating agents :
CO
Flavanthrene is commercial under the name Ind-
anthrene yellow (E.P. 24,354 (1901) ).
In the course of this research, Scholl found that
dimethyldianthraquinonyl (I.) can itself be dehydrated,
giving a new product, pyranthrone y which has the con-
stitution :
ANTHRACENE DYESTUFFS 227
it dyes vegetable fibres from a vat yellowish orangr
shades (Seholl, Ber. 9 1911, 44, 1448), and comes into
commerce as Indanthrene golden orange G. It is very
fast to light and bleaching. Its halogenated derivatives
are known as Indanthrene golden orange R and Indan-
threne scarlet G, the latter being probably a dibromo-
derivative, produced by bromination in the presence of
nitrobenzene.
Benzanthrone.
In a research on Prudhomme's reaction, Bally (Ber.,
1905, 38, 194) noticed that on heating /3-amidoanthra-
quinone with glycerine and sulphuric acicl, it is converted
into benzanthrone quinolin-e (I.), and under the same
conditions anthraquinonc and oxanthranol react to give
benzanthrone (II.) :
When benzanthrone qu incline is fused with a caustic
alkali, a vat blue is obtained, Cyanthrene, whilst under the
same conditions two molecules of benzanthrone condense
to give a violet dyestuff, Violanthrenc BS, or Indanthrene
dark blue BO (E.P. 16,538 (1904), 22,519 (1905) ). This
dyesttfff gives reddish violet shades on cotton, which
are turned blue by washing. Indanthrene violet RT is
a halogen derivative, and is an extremely fast dyestuff.
Indanthrene green is a nitre-derivative.
228
ORGANIC DYESTUPFS
Scholl and Mansfeld (Ber., 1910, 43, 1734) have
recently described the mesobmzdianthronc which is formed
by the reduction of dianthraquinonyl by means of copper
and sulphuric acid :
Dianthraquinonyl itself is obtained by treating anthra-
quinone a-sulphonic acid with ammonia, converting the"
amidoanthraquinone produced into an iodo-derivative
by diazotising and the Sandmeyer reaction, and treating
this product with powdered copper.
On heating mesobenzdianthrone with aluminium
chloride, it loses hydrogen and gives mesona/phthodi-
anthrone :
ANTHRACENE DYESTUFFS 229
Anthraquinoneimides.
The dyestuffs of this class were shown by F. Ullmann
to be formed by the linking up of several molecules of
anthraquinone by means of NH groups, and are obtained
by condensing amidoanthraquinones with halogen deri-
vatives of anthraquinone in presence of small amounts
of copper salts, generally with the addition of anhyd-
rous sodium acetate. To this class belong Indanthrene
red G, obtained by condensing one molecule of 2 : 6-
dichlor-anthraquinone with two molecules of a-amido-
ant hraquinone (E.P. 4235 (1907) ), Indanthrene bordeaux
B (B.A.S.F., E.P. 10,324 (1907) ), and Algol orange R
(E.P. 24,810 (1908) ), red B (E.P. 13,686 (1907) ), and
bordeaux 3B (E.P. 9219 (1909) ) of the Bayer Co.
Algol grey B (E.P. 5382 (1909) ) is obtained by nitrating
the trianthramide obtained from 1 : 5-diamidoanthra-
quinone and two molecules of a-chloranthraquinone ?
and reducing the product with an alkali sulphide.
Acylamidoanthraquinones.
Beiizoyl-l-anridoanthraquinone :
Nil CO C 6 H 5
is a vat dyestuff, which dyes cotton rich yellow shades
(Bayer, B.F.< 400,663). It is remarkable that such a
simple compound should have the same properties as the
much more complex compounds of the above classes. It
is not, however, an isolated case, as the dibenzoyl-deriva-
tives of the diamidoanthraquinones, and of the oxy-
diamidoantbraquinones, and also their succinyl-deriva-
tives, and, generally, the acylated derivatives of these
amines, form vat dyestuffs. The following table of these
acylamido vat dyestuffs is of a representative character :
230
ORCMNIC DYESTUFFS
Algol yellow WO.
R.
Algol red 5G.
,, R extra.
Algol pink R.
Algol scarlet G.
Algol blue 3R.
Algol Brilliant
violet 2B
Algol Brilliant
orange FR.
Algol Brilliant red
2B
Algol Brilliant
violet R.
Algol olive R.
Algol violet B.
Helindone yellow
3GN.
E.P. 27,078
(1908).
E.P. 3055
(1909).
D.R.P. 223,232.
E.P. 5786
(1909).
D.R.P. 225,232.
Do.
D.R.P. 225,232.
Do.
Do.
D.R.P. 225,232,
228,992.
D.R.P. 225,232.
D.R.P. 232,739.
Benzoy 1- 1 -amidoanthra-
quinone.
Succinyl-( 1-amidoanthra-
quinono). 2 .
Dibenzoyl-1 : 5-diamido-
anthraquinono.
Dibonzoyl-1 : 4-diamido-
an thraquinone .
Dibenzoyl-1 : 5-diamido-8-
hydroxyan thraquinone .
Berizoyl-4-amido- 1-hydr-
oxy an thraquinone.
Benzoyl- l-amido-4-meth-
oxyanthraquinone.
Dibeiizoyldiamidoanthra-
rufin.
Do.
Benzoyl- 1 : 2 : 4-triamido-
an thraquinone.
1 : 5-Dibenzoyldiamido-4-
hydroxy an thraquinone .
Succiny Idiamidoan thraqui -
none.
Chlorsulphonic acid on di-
benzoyldiamidoan thra-
quinone.
Benzoylamido-4 : 6 : 8-tri-
hydroxyan thraquinone.
Urea derivative of two
molecules of /3-amido-
a nthraquinone .
Certain of these acylated derivatives, such as the
acetyl derivatives of the a-amidoanthraquinones, may
again be dehydrated to give a new ring, pyridone :
CO
NH
H 2
CO
ANTHRACENE DYESTUFFS
231
This pyridone grouping may also be present in more
complex molecules, for example, Algol red B is an anthra-
quinone-imide which contains the pyridone ring :
CO
Although anthraquinone is a cheap raw material, a
fact which has led to great activity in the preparation
of vat dyestuffs derived from it, its use is limited on
account of the relatively small proportion of the new
products which have a marked affinity for the fibre. The
complex character and high molecular weight of certain
of these dyestuffs, together with the absence of nitrogen,
are interesting features ; thus the empirical formula of
Indanthrene violet R, C :M H 1( ,O.,, approaches that of a
hydrocarbon. That such a substance should form a
soluble leuco-compound is remarkable, and it has been
suggested that the leu co -compound is in colloidal solution.
The Anthraquinone vat dyestuffs generally require a
more strongly alkaline vat than the Indigoid dyestuffs,
and have hence, with few exceptions, been applied exclu-
sively to the dyeing of cotton. Kami (Fnrb.-Ztg., 1914,
25, 73) points out that these vat dyestuffs may be used
for dyeing wool which has been treated with formalde-
hyde to render it stable to alkalies.
232 ORGANIC DYESTUFFS
New vat dyestuffs of the Anthraquinone series have
been obtained by the action of diazo-anthraquinone on
certain aromatic amines which are not suitable for
combining to form normal Azo-dyestuffs, or by the
action of aromatic diazo-compounds on amidoanthra-
quinones (Chem. Fabrik Griesheim-Elektron., E.P. 8422
(1912) ). These new dyestuffs probably have the
general formula R! N =N NR 2 R 3 , where Rj and
R 2 are aromatic radicles, of which one must be of the
anthraquinone series, and R 3 may be H, CH 3 , or a similar
radicle.
CHAPTER XX.
QUINONE-IMIDE DYESTUFFS.
THE quinone-imide derivatives include certain dye-
stuffs related to quinones. When hydroquinone is
oxidised, quinone is obtained, but for a long time
it was not found possible to isolate similar products
resulting from the oxidation of ^-amidophenol or
p-phenylenediamine. When this oxidation is carried
out by means of hypochlorites, quinonechlorimide and
quinonedichlor-di-imide are obtained respectively :
0=C 6 H 4 =NC1 C1N=C 6 H 4 =NC1.
Willstatter (Ber. 9 1904, 37, 1494 and 4605) has suc-
ceeded in isolating quinoneimide and quinone -di-imide :
0=C 6 H 4 =NH NH=C 6 H 4 =NH.
Certain dyestuffs may be considered as derived from
the ;p-quinoneimides, others as derivatives of the
o-quinoneimides. The Indamines and the Indophenols
are derived from p-quinone. The Oxazines, the Thia-
zines, and the Azines are or^o-quinonoid derivatives.
This distinction is not generally recognise&p certain
authors considering all these dyestuffs to" be p-quinonoid
derivatives. (Compare Kehrmanu, Havass, and Grand-
mougin, Ber., 1913, 46, 2131.)
(1) Indamines.
The Indamines were discovered in 1877 by Nietzki,
who established their constitution. They are produced
by oxidising an equimolecular mixture of a ^-diamine
and a nionamine in cold dilute solution . The conditions
234 ORGANIC DYESTUFFS
which should be fulfilled by these amines are as follows :
the >-diamine should have one free NH 2 group, the other
may be substituted ; the monamine may be a primary,
secondary, or tertiary amine, but the ^para-position to
the amido-group must be free. For example, the oxida-
tion of a mixture of c^ra.-dimethyl-^-phenylenediamine
and dimethylaniline in acid solution gives an Indamine :
Oxidation eliminates the hydrogen atoms of the NH 2
group of the 2>-diamine, and also one hydrogen from
the nucleus of the monamine from the ^-position to
the amido-group. This is established by the reduction
of the Indamines, derivatives of p-diamidodiphenyl-
amine being obtained :
C1.R 2 N = C 6 H 4 =N C G H 4 NR 2 + H 2
R 2 N C 6 H 4 NH C 6 H 4 NR 2 + HC1.
These diphenylarnines are leuco-derivatives of the
Indamines , which are regenerated on oxidation . Finally,
the fact that monamines in which the 2?ara-position is
occupied do not give Indamines, proves that combination
takes place in thepara-positiori.
Indamines are also obtained by the action of nitroso-
derivatives of tertiary amines on amines in which the
para-position is free ; thus nitrosodimethylaniline hydro-
QUINONE-IMIDE DYESTUFFS 235
chloride condenses with amines in which the para-
position is free :
N =C 6 H 4 =N OH +C 6 H 5 NR 2
I
Cl
4 =N C 6 H 4 NR 2 + H 2 O
j
Cl
The Indamines are highly coloured compounds which
form blue or green salts soluble in water. They are
very sensitive to the action of acids, which hydrolyse
them, giving quinone. It is for this reason that the
Indamines are not used in dyeing, but are mainly used
as raw materials for the manufacture of the Oxazines,
the Thiazines, and the Azines.
Phenylene blue is the simplest Indamine, being first
obtained by Nietzki (Ber., 1883, 16, 464) by oxidising a
solution of a mixture of ^-phenylenediamine and aniline
with potassium dichromate.
Bindschedler's grAen, or tetramethyl-indamine :
(CH^ =C 6 H 4 = N C 6 H 4 N(CH 3 ) 2
Cl
is obtained by oxidising an equimolecular mixture of
dimethyl-p-phenylenediamine and dunethylaniliiie (Bind-
schedler, Ber., 1883, 16, 865), or by first oxidising the
dimethyl-p-phenylenediarnine and treating the inter-
mediate red compound (" Wurster's red ") obtained, with
dimethylaniline. Wurster's red was at first considered
to be the methyl chloride compound of methylquinone-
di-imide :
>* V + o -
A
H Cl
01
236 ORGANIC DYESTUFFS
but recent experiments (Willstatter and Piccard, Ber.,
1908, 41, 1458) have shown that Wurster's red is a
quinhydrone, that is, the compound of a molecule of the
quinonoid salt with a molecule of the base. Compounds
of this type are called "*meri "-quinones by Willstatter,
the quinonoid salts being called <c holo "-quinones.
Witt has prepared tetramethyl-indamine by con-
densing nitrosodimethylaniline with dimethylaniline.
Toluylene Blue is formed by the oxidation of a mixture
of a molecule of climethyl-^-phenylenediamine and a
molecule oi w-toluylenediamine, or by the action of
nit rosodimethy] aniline hydrochloride on w-toluylene-
diamiiie ; it has the following constitution :
Preparation of Bindschedler' s Green.
A mixture of 13-6 parts of dimethyl -^-phenylene-
diamine and 12-1 parts of dimethylaniline is dissolved in
400 to 500 parts of water, to which have been added
20 parts of concentrated hydrochloric acid. This solution
is cooled by immersion in ice, and is oxidised by a solution
of 20 parts of potassium dichromate and 6 parts of acetic
acid in 200 parts of water: The dyestuff is immediately
formed, and is partly precipitated. Sufficient water is
added to re-dissolve it, the solution is heated to 40-50
and zinc chloride added. On cooling, the zinc chloride
compound of the dyestuff crystallises out.
QUINONE-IMIDE DYESTUFFS 237
(2) Indophenols.
The Indophenols are dyestuffs of which the properties
and methods of preparation are very similar to those of
the Indamines. The first Indophenol was discovered by
Kochlin and Witt in 1881 by oxidising an equimolecular
mixture of dimethyl-^>-phenylenediamine and a-naphthol
(D.R.P. 15,915 ; Kochlin, Bull. Soc. ind. de Mulhouse,
1882, 532 ; 0. Witt, J. Soc. Chem. Ind., 1882, 255).
The Indophenols are produced by oxidising a p-di-
amine in presence of a phenol or naphthol in which
the jrara-position is free. As in the case of the Indamines,
it is necessary that the diamine shall have one amido-
group free, the other may be substituted. The oxida-
tion is carried out in dilute acetic acid solution by means
of potassium dichromate, or better in alkaline solution by
means of hypochlorites, or merely by passing in air, in
which case the addition of a trace of a copper salt aids
the oxidation. There are two ways of explaining this
reaction according to whether the quinonoid structure
is formed in the amine nucleus, or in that of the phenol :
(I.) NH 2 C 6 H 4 NH 2 + C 6 H 5 OH + 2
= 2H 2 + NH=C 6 H 4 = N C 6 H 4 OH.
(II.) NH 2 C 6 H 4 NH 2 + C 6 H 5 OH + 2
= 2H 2 + NH 2 C 6 H 4 N=C 6 H 4 = 0.
Hence, there are two possible constitutions. As the
Indophenols have no acid properties, being insoluble
in alkalies, but, on the other hand, have weak basic
properties, they cannot be supposed to contain a phenol
group, but must contain the basic NH 2 group. Thus the
simplest Indophenol has the constitution :
NH 2 C 6 H 4 N = C 6 H 4 = O.
Indophenols are also formed by the action of nitroso-
dimethylaniline or quinonechlorimides on phenols or
naphthols.
238 ORGANIC DYESTUFFS
Properties. The Indophenols are very sensitive to the
action of acids, by which they are decomposed, giving
quinones. On reduction, the Indophenols are decolorised,
giving leuco-Indophenols, which are soluble in alkali, and
which regenerate the original substance on oxidation.
The use of Indophenols in dyeing depends on this
property. -^
NH 2 -C 6 H 4 --N = C 6 H 4 = t NH 2 -C 6 H 4 -NH-C 6 H 4 -OH.
Indophenol is the only important dyestuff of this class.
It is obtained by oxidising an equimolecular mixture
of a-naphthol and dimethyl-p-phenylene diamine, its
constitution being :
(CH 3 ) 2 N C 6 H 4 N = <( \ =0
It crystallises from benzene in bronze-coloured needles,
and is hydrolysed by acids, giving a-naphthoquinone,
which shows that the quinonoid structure is in the phenol
nucleus.
The Indophenols now find no application as dyestuffs,
and are only used as raw materials for the preparation
of Sulphur dyestuffs (p. 307).
Preparation of Indophenol.
144 grm. of a-naphthol are dissolved in 250 ccs. of
water containing 6 grm. of caustic soda, and a solution
of 13-6 grm. of dimethyl-p-phenylenediamine in 250 ccs.
of water added, the whole being then oxidised by means
of sodium hypobromite, prepared by slowly pouring 32
grm. of bromine into a well-cooled solution of 20 grm.
caustic soda in 150-200 ccs. water ; the temperature
should not rise above 5 C. Under these conditions the
Indophenol is precipitated ; it is allowed to settle, and
is then separated, dried, and crystallised from benzene.
QUINONE-IMIDE DYESTUFFS 239
(3) Thiazines.
The Thiazines are dyestuffs which contain a charac-
teristic ring containing nitrogen, carbon, and sulphur :
N
\/ \/
C
II I
O
These dyestuffs are related to a sulphur base, thio-
diphenylamine, in the same way that the Indamines
and Indophenols are related to diphenylamine. By
introducing auxochromes in para-position into di-
phenylamine leuco-Indamines or leuco-Indophenols are
obtained, which are converted into dyestuffs by oxidation.
On melting diphenylamine with sulphur, a new base is
obtained, thiodiphenylamine :
NH NH
2S = H 2 S
in which it is only necessary to introduce the auxo-
chromes NH 2 , NR 2 , OH in jpara-position to the nitrogen
to obtain leuco-derivatives of the Thiazines. Thus
p-diamido-thiodiphenylamine :
NH 2
240 ORGANIC DYESTUFFS
yields on oxidation in acid solution a violet dyestuff,
Lauth's violet.
Before the quinonoid theory was generally accepted,
the thiazine ring was considered to be a chromophore.
Since that time these ideas have been modified, the
chromophoric function being attributed to the quinonoid
structure which is formed on oxidation of the leuco-
thiazines. For a long time this chromophore was
considered to be para-quinonoid (I.) ; at the present time
this grouping is considered to have an orJAo-quinonoid
structure, the sulphur atom being basic and tetravalent,
(II.) :
+ O -f HOI
or
NH
-f O -f HOI
NH 2
01
QUINONE-IMIDE DYESTUFFS 241
This second method of formulation is supported by a
number of experimental facts which are too long to
detail in this book (see Kehrmann, Ber., 1899, 32, 2601 ;
Green, ibid., 3155), and has the advantage of representing
by similar formulae the Azines, the Oxazines, and the
Thiazines, which have very similar properties. To
suggest the basicity of the sulphur in these molecules,
the Thiazines have been called azthionium derivatives
(Kehrmann, Ann., 1902, 322, 1 ; 1910, 372, 287). By
keeping the older method of writing (Formula I.) the
Thiazines become Ind amines or Indophenols in which
the two benzene nuclei are also linked by a sulphur
atom. This results in a greater stability of the molecule,
which is no longer destroyed by acids. The Thiazines
may be divided into two classes : the Thiazimes, corre-
sponding to the Indamines ; the Thiazoties, correspond-
ing to the Indophenols. The Thiazitnes (Amido-
Thiazines) are the most important.
Amido-Thiazines (Thiazimes).
Historical. The first Thiazine dyestuff was discovered
by Lauth (Compt. rend., 82. 1441 ; Bull. Soc. chim.,
1876, 422) by a reaction which is named after him, and
which consists in oxidising ^-phenylencdicimine in. acid
solution by means of ferric chloride in presence of sul-
phuretted hydrogen. The product is called Lauth' s
violet or Thionine, and is also formed by oxidising the
product obtained by the action of sulphur on ^-pheny-
lenediamine. At about the same time, Caro (Ber.,
1878, 11, 1705) prepared Methylene, blue by applying
Lauth's reaction to dimethyl -_p-phenyleiiediamine. Koch
(Her., 1879, 12, 592) found that only the j9am-diamines
gave Lauth's reaction, ammonia being eliminated. The
detailed researches of Bernthscn (Ann., 1885, 230,
73 ; 1889, 251, 1) definitely established the constitution
of the Thiazines and led to the discovery of new processes
for their preparation, which were of great theoretical
242 ORGANIC DYESTUFFS
and commercial interest. Lauth's reaction only gives
small yields, whereas Bernthsen's method gives excellent
yields.
Lauth's violet, or diamidodiphenazthionium chloride,
Two methods of preparation have already been
outlined: (1) oxidation of jp-phenylenediamine with
ferric chloride in presence of sulphuretted hydrogen ;
(2) fusion of p-phenylenediamine with sulphur, and
oxidation. It is also obtained by oxidising a mixture of
p-phenylenediamine and aniline in presence of sodium
thiosulphate.
Bernthsen has proved its constitution as follows :
thiodiphenylamine gives on treatment with nitric acid
a p-dinitro derivative which on reduction yields diamido-
thiodiphenylamine, which is identical with leuco-
thionine. The base forms a crystalline powder soluble
in alcohol to a violet solution. Lauth's violet, its hydro-
chloride, crystallises in glistening needles.
Methylene blue, or tetramethyldiamidodiphenazthio-
nium chloride :
lN(OH 3 ) 2
QUINONE-IMIDE DYESTUFFS 243
was first obtained by Caro by oxidising dimethyl-jp-
phenylcncdiamine with ferric chloride in presence of
sulphuretted hydrogen. The process patented by the
B.A.S.F. consists of converting dimethylaniline into its
nitroso-compound, and then reducing this derivative
with sulphuretted hydrogen. In this reaction there is
formed the leuco-derivative of the dyestuff , together with
dimethyl -p-phenylenediamine. On addition of ferric
chloride, the dyestuff is produced, and may be precipitated
by the addition of common salt and zinc chloride. The
yield is small ; moreover, two molecules of the diamine
enter into the reaction, ammonia being eliminated. This
process has been replaced by the thiosulphate process
of Bernthsen (D.E.P. 38,573; 39,757; 45,839; 46,805),
which in addition to giving a better yield, has the
advantage of replacing one molecule of dimethyl-p-
phenylenediamine by a molecule of the less expensive
dimethylaniline. According to D.R.P. 46,805 the method
is as follows : 6 kilograms of dimethylaniline are con-
verted into the nitroso- com pound, which is then reduced
by zinc dust. The product is diluted to give about 250
litres of solution, which are neutralised with caustic soda
until a permanent opalescence is obtained. Sixteen
kilograms of aluminium sulphate are then added, and
after stirring for half an hour, a solution of 13 kilograms
of sodium thiosulphate is poured into the mixture, which
is then oxidised by means of 4-8 kilograms potassium
dichromatc dissolved in 75 litres of water. After
stirring for an hour, the liquid is diluted to 600 litres
with water, and 6 kilograms of dimethylaniline added
in the form of its hydrochloride. A saturated
solution of 14 kilograms of potassium dichromate is
added fairly quickly at a temperature not exceed-
ing 10-12 C., and then a solution of 65 kilograms
zinc chloride (142 Tw.) added, and the liquid boiled for
half an hour. On cooling, Methylene blue crystallises
out.
Theory of the Reaction. Bernthsen (loc. cit.) has shown
244 ORGANIC DYESTUFFS
that, on oxidising with potassium dichromate in the cold,
p-diamines in presence of sodium ihiosulpJiatc, or better
in presen.ce of aluminium thiosulphatc, form well defined
crystalline thiosulphonic acids. Thus, in the above
example, dimethyl-j;-phenylenediamine in presence of
thiosulphate and an oxidising agent gives :
N(CH 3 ) 2 N(CH 3 ) a
-f IIS SO 3 H + O = H 2 O -f
' - S - S0 3 H
the aluminium thiosulphate, being hydrolysed, acts as
free thiosulphuric acid and dimethyl-p-phenylenediamine
thiosulphonic acid is obtained, the constitution of which
was established by Bernthsen. By oxidising this acid
in presence of a further molecule of dimethylaniline an
Indaraine thiosulphonic acid is formed :
NH 2
(CH 3 ) 2 N S S0 3 H N(GH 3 ) 2
-f 2H 2
(CH 3 ),N" S N(CH 3 ) 2
On heating in dilute acid solution, this compound gives
sulphurous acid, of which one portion is eliminated,
whilst another portion of the acid converts the dyestuff
into its leu co-derivative.
QUINONE-IMIDE DYESTUFtfS
HOI
The thiosulphonic acids may be converted into
mercaptans by reduction :
and these compounds on oxidising in presence of amines
first yield mercaptans of the Indamines and then dye-
stuffs.
Methylene blue is hence the tetramethyl-derivative
of Lauth's violet, although it cannot be obtained by
methylating this compound. Commercial Methylene
blue is the zinc chloride compound :
2C 16 H 18 N 3 SC1 + ZnCl 2 + H 2 0.
It is a basic dyestuff which is much used for dyeing
cotton mordanted with tannin. The free base can only
be obtained by treating the hydrochloride with silver
hydroxide.
Owing to its high tinctorial power, Methylene blue
has been used in analytical chemistry for the detection
and estimation of many reducing and oxidising agents.
(See Knecht and Hibbert, New Reduction Methods in
246 ORGANIC DYESTUFFS
Volumetric Analysis ; also Atack, J. Soc. Dyers and
Col, 1913, 9 ; Analyst, 1913, 99 ; J.C.8., 1913, 1319.)
It has also been recommended for use in place of starch
for iodimetric titrations (Sinnatt, Analyst, 1910, 35,
309 ; 1912, 252).
On nitration, Methylene blue gives Methylene green.
On exposure to air, alkaline solutions of Methylene blue
give a new dyestuff, Methylene azure, which differs from
the original dyestuff by the loss of one of the methyl
groups. This dyestuff has a greater intensity, and
dyes redder shades than Methylene blue, and is prepared
by the B.A.S.F. by oxidising this dyestuff with bi-
chromate in sulphuric acid solution. The Basle Soci<t!
has shown that oxidation with permanganate in alkaline
solution gives a different result ; in all probability a
sulphone or sulphoxide is produced.
New Methylene blue is obtained from diethyl-o-tolui-
dine and the Thiocarmines from ethylbenzylaniline
sulphonift acid.
(4) Oxazines.
The Oxazines are very similar to the Thiazines,
differing by the substitution of an oxygen atom for the.
characteristic sulphur atom. In the same manner that
thiodiphenylamine is considered the parent substance
of the Thiazines, so the Oxazines may be considered to
b# derived from diphenoxazine :
/Nil
This base is obtained by condensing o-diamidophenol
with pyrocatechol. If auxochromes are introduced in
para-position to the nitrogen, leuco-Oxazines are ob-
tained, which on oxidising yield dyestuffs. According
to whether these auxochromes are amido- or alkylamido-
QUINONE-IMIDE DYESTUFFS 247
groups, or hydroxy-groups, these dyestuffs are called
Oxazimes or Oxazones.
The Oxazines are generally obtained from o-hydroxy-
derivatives of the Indamines or Indophenols, which are
readily converted into Oxazine dyestuffs, the preparation
of which hence involves that of o-hydroxy-Indamines or
Indophenols, which may be carried out in several ways :
(1) Nitroso -derivatives of tertiary amines or of phenols
are condensed with phenols or naphthols in which the
yarn-position is occupied ;
(2) In the above reaction the nitroso derivatives may
be replaced by the corresponding quinonechlorimides ;
(3) Nitroso-derivatives of the m-amidophenols are
condensed with amines.
In these reactions it is necessary to use an excess of
the nitroso- or quinonoid compound, this being reduced
by the hydrogen liberated during the reaction.
Amido-Oxazines (Oxazimes).
The simplest dyestuff of this series is the oxygen
analogue of Lauth's violet :
This compound is only of theoretical interest, being
obtained by nitrating phenoxazine, reducing the nitro-
derivative, and then oxidising the product formed.
Capri blue may be considered to be the higher
homologue of the tetramethyl-derivative of the above
compound. It was obtained by Bender in 1890 (Leon-
hardt & Co., D.R.P. 62,367) by condensing nitroso-
dimethylaniline with dimethyl-w-amidocresol :
248
ORGAN 1(1 DYESTUFFS
NO CH 3
+ HOI
(CH 3 ) 2 N
IIO N(CH 3 ) 2
N 01 f 3
(CII 3 ) 2 N
N(CI 3 ) 2
The methyl group of the cresol derivative causes
condensation of the phenol group to take place in ortho-
position. The hydrogen liberated reduces a molecule
of the nitroso-compound to dimethyl-p-phcnylene-
diamine. The commercial product is the zinc chloride
compound of the dyes tuff. It is a basic dycstuff, which
dyes tanned cotton a greenish blue, and forms glittering
reddish-brown cryst als .
Naphthol blue or Meldola's blue, was discovered
by R. Meldola (Her., 1879, 12, 2065) by condensing
nitroso-dimothylaniline hydrochloride with /3-naphthol
in alcoholic solution in presence of zinc chloride :
NO
+ 1101
(<'H 3 ) a N
1 2 + H 2 O
QUINONE-IMIDE DYESTUFFS 240
Preparation. 14 grams of /3-naphthol are dissolved
in the same weight of glacial acetic acid, and heated to
110. 18-5 grams of nitrosodimethylaniline hydro-
chloride are then added in small portions, when a
vigorous reaction occurs. When all the hydrochloride
has been added, the mass is poured into water. A tarry
black mass separates, which is dissolved in boiling
alcohol ; hydrochloric acid is added to the filtered
solution, and, on cooling, reddish-brown needles of the
hydrochloride of the dyestuff separate.
The commercial product is the zinc chloride com-
pound, which crystallises in bronze coloured needles
and is known as New blue R, New Fast Cotton blue,
Naplithylene blue, Cotton blue R, Fast Marine blue, etc.
It is used for dyeing cotton mordanted with tannin,
which it dyes an indigo blue.
In the above preparation, if /3-naphthol is replaced by
2 : 7-dihydroxynaphthalene, a very pure blue dyestuff
known as Muscarine is obtained, the constitution of
which is as follows :
(CH 3 ) 2 N
It forms crystals with a copper reflex. Its free base
is soluble in caustic alkalies, but not in ammonia.
Nile blue is the amido-dcrivative of Meldola's blue,
and was discovered by Reissig at the B.A.S.F. in 1888
(D.R.P. 45,208) by condensing nitrosodiinethyl-m-
amidophenol with a-naphthylamine :
250
ORGANIC DYESTUFFS
NO
(CH 3 ) 2 N
HC1
OH
\
NHn
-f- H 9 -f Ho
Nile blue A is the corresponding diethyl-derivative.
The dyestuff obtained from benzyl-a-naphthylamine is
known as Nik blue 2B. They are all basic dyes tuffs,
dyeing tanned cotton very pure greenish blue shades.
Witt has given the name Cyanamines to dyestuffs
produced by the action of primary or secondary amines
on Meldola's blue. Thus dimethylamine gives with this
dyestuff a new product, New Methylene blue N.0.0.
(Nietzki and Bossi, Ber., 1892, 25, 3002) :
(CH ) 2 N
\
N(CH 3 ) 2
Aniline gives the corresponding phenyl derivative. In
these reactions hydrogen is liberated, and this converts
the dyestuff into its leuco-compound.
QUINONE-IMIDE DYESTUFFS 251
Oxazones.
The simplest Oxazone :
was obtained by Kehrmann by oxidising diphenoxazine.
The most important compounds of this class are Reso-
rufine, or hydroxydiphenoxazone, and Resazurine, both
of which are produced by the action of nitric acid con-
taining nitrous fumes on an ethereal solution of resor-
cinol. The formation of Resorufine is explained by the
action of the nitrosoresorcinol on the excess of resorcinol :
OH
-f 2H 2 o
o b OH
It forms small reddish-brown crystals. Its tetrabrom-
dcrivativo is Fluorescent blue, which dyes wool and silk
blue with a red fluorescence. Resazurine is produced
by the oxidation of Resorufine.
Oxazime-Oxazone Dyestuffs.
The simplest of these compounds is Resorufamine,
which is formed by the action of quinonedichlordiimide
on resorcinol. Its methyl derivative, dimethylresoruf-
amine, is obtained by condensing nitrosodimethylaniline
252
ORGANIC DYESTUFFS
with resorcinol. It is a basic dyestuff which gives a
very fast blue lake with tannin . This lake is produced
directly on the fibre by printing with a thickened
mixture of nitrosodimethylaniline, resorcinol, and tannin,
drying, and steaming, when the lake formed remains
fixed 011 the fibre.
Gallocyanine was discovered by Kochlin in 1881
(D.R.P. 19,580) by heating riitrosodimethyl aniline in
alcoholic or acetic acid solution with gallic acid. The
dyestuff crystallises in green needles ; the mother liquor
contains dimethyl-jp-phenylencdiamine. Gallocyanine is
produced as follows :
coon
NO
(CH 3 ) 2 N
+ H 2 0+H 2
This formula was suggested because the methyl ester
of Gallocyanine behaves as a dihydroxy-compouud, but
Kehrmann considers that the compound contains a
carboxyl group, and gives it the following constitution
N COOH
XV
(cir 3 ) 2 N
'v/
on
QUINONE-IMIDE DYERTUFFS 253
It dyes on metallic mordants ; with chromium
hydroxide it gives a violet lake much used in calico-
printing. Owing to its insoluble character, Gallocyanine
has not been satisfactory for printing, although largely
used for dyeing wool. The leuco-compound is more
soluble, and gives more intense and brighter shades in
combination with chromium acetate. Modern violet,
blue (1900), etc., are leuco-compounds of Gallocyanine,
Gallumine blue, C destine blue, etc. Modern heliotrope PH
is obtained by condensing nitroso-monoethyl-o-toluidine
with gallamide, and subsequently reducing to the leuco-
compound. The Ultra violet dyestuffs [S.] are quin-
hydrones obtained by condensing a Icuco-Gallocyanine
with a Gallocyanine. On heating Gallocyanine base
with water, the carboxyl-group is eliminated (Bayer Co.,
D.R.P. 192,971):
These Pyrogallocyanines are commercial as leuco-
compounds, which are extremely soluble, such as
Gallo violet [By.] and Modern violet N [D.H.], the
chrome lakes of which are easily developed by
steaming.
The condensation of Gallocyanines with aromatic
alkylatcd din-mines possessing a free amido-group, yields
a new series of dyestuffs, such as the Modern Cya nines,
Anthracyanines, Chromeaeetine bine, and Modern blue
CV1, \\liich are easily fixed with chromium acetate, and
have largely replaced the older brands of Phonocj r aiiiiies.
During the reaction, half of the Gallocyanine used is
254 ORGANIC DYE8TUFFS
reduced, and can no longer react with amine. Hence
the yield of Delphine blue B [S.] :
NH.C ri H 4 .SO s .NH 4
prepared by the action of aniline on Gallocyanine and
subsequent sulphonation, is much improved by blowing
air into the mixture to oxidise the leuco-Gallocyaniiie.
Chromazurine G and E [D.H.] appear to be isomeric
with Delphine blue. These dyestuffs give blue shades
on chrome mordant.
The dyestuff known as Prune is obtained by con-
densing nitrosodimethyl aniline with methyl gallate ; it
is a basic dyestuff having the constitution :
COOCH.
(CH 3 ) 2 N O OH OH
Nitrosodimethylaniline and gallamidc yield Gallamine
blue, which on heating with aniline gives Gallanil blue,
of which the sulphonic acid is known as Gallanil indigo,
and the nitro-derivative as Gallanil green (see Ritter-
mann, Farb.-Ztg., 1912, 282, 802).
(5) Azines.
The Azines arc closely related to the Indamines and
the IndopJienols. Thus, on heating an aqueous solution
QUINONE-IMIDE DYESTUFFS 255
of an o-amido-Iudaminc it is converted into an Azine
with liberation of hydrogen. For example, if a solution
of Toluylene blue is heated, it gradually becomes red,
owing to the formation of an Azine, Toluylene red :
The hydrogen liberated reduces part of the dyestuff
to its leuco-compound. This relation between the
Azines and the Indamines seems to indicate a similarity
in their constitution and the Azines have for a long time
been considered as jpara-quinoiioid compounds. Facts
are, however, known which are against such a struc-
ture. Thus on oxidising o-hydroxydiamidodiphenyl-
amine, there is obtained under certain conditions an
Azine, amidophenazine :
NH
OH NH 2 NH 2 NH
This compound, however, contains a free amido-
group, which cannot be brought into agreement with a
256 ORGANIC DYESTUFFS
paro-quinonoid" constitution. This formula was hence
replaced by the formula :
N
N
but this does not contain the chromophore, the quinonoid
group, and was hence replaced by the following formula,
which represents Azines as or^o-quinonoid compounds :
N
s/V
N NH 2
The nitrogen atoms of the azine ring have very decided
basic properties, it is considered that in the formation
of salts, the molecule of acid becomes attached to one
of these atoms. The chromophore of the Azines should
hence be :
H Cl
Diphenazine hydrochlorido, or phonazonium chloride.
It will be seen that there is a very great analogy
between the constitution of the Oxazines, the Thiazines,
and the Azines, if the former are represented by formulae
in which oxygen and sulphur are tetravalent.
The Azine dyestuffs may all be considered as phenaz-
onium derivatives, and have various names :
The mono- and di-amidodiphenazines are called
Eurhodines,
QUINONE-IMIDE DYESTUFFS
257
The mono- and di-hydroxydipheuaziiies are called
Eurhodoles.
The meso-iphvnyl derivatives of the Eurhodines
(diamido) are the Safranines :
N
NH
NH 9
The raeso-phenyl derivatives of the Eurhodoles are
called Safranoles.
The Mauveines are Safranines in which the phenyl
radicle is substituted for one hydrogen in the amido-group.
Finally, the phenylamido- derivatives of the Mauve'mes
are called Indulines.
Safranines from which one of the amido-groups have
been eliminated are known as Aposafranines, which
have particular names if derived from naphthophen-
azine, according to the position of the amido-group ; if
this is present in the naphthalene nucleus, they are
termed Rosindulines, if present in the other nucleus,
Isorosindulines :
N N
N
5
N
C 6 II 6 Cl
Aposafraiiino.
C 6 H 5
Rosinduline.
Cl
N
N
C 6 H 5 01
Isorosinduline.
O.D.
258 ORGANIC DYESTUFFS
Eurhodines.
These were discovered by Witt (Ber., 1886, 19, 441)
by heating o-ainidoazo-compounds with amines. They
may also be obtained :
(a) By heating o-amido-Indamines in aqueous solu-
tion ;
(b) By oxidising certain o-diamines ; thus o-phenylene-
diamine gives os?/m.-diainidodiphenazine.
(c) By condensing nitroso-derivatives of tertiary
amines or quinonedichlordiimides with amines in which
the jara-position is occupied ;
(d) By oxidising certain triamido-derivatives of di-
phenylamine, thus o-di-_p-tri-amido-diphenylamine gives
diamidodiphenazine ;
(e) By condensing ortfAo-quinones with amido-deriva-
tives of ortfAo-diamines.
Properties. The Eurhodines are weak bases of which
the monoacid salts are red and the diacid salts green ;
these salts are hydrolysed by water.
The most important compound of this class is Toluylene
red, which is derived from Toluylene blue, and is most
easily prepared by oxidising a warm mixture of di-
methyl -^-phenylenediamine and ra-toluylenediamine. It
is commercial as Neutral red, and gives red shades on
tanned cotton.
Neutral violet is the lower homologue, obtained by
using w-phenylenediamine (Witt, Her., 1879, 12, 931 ;
D.M.P. 15,272).
Eurhodoles.
These compounds are obtained by heating Eurhodines
with concentrated hydrochloric acid at 180, or by the
alkaline fusion of the sulphonic acids of the Azines,
or by condensing hydroxy-orffo-quinones with ortho-
diamines.
QUINONE-IMIDE DYESTUFFS 259
Safranines.
Historical. Perkin was the first to manufacture a red
dyestuff, Mauve'ine being first prepared by him in 1861.
It was patented by D. Price in England and by F. Duprey
in France in 1869. These two processes consisted of
oxidising aniline iii acid solution by means of lead
dioxide or barium peroxide. Safranine was manufac-
tured at Basle in 1868, and in England by Caro in 1871.
Later Nietzki obtained a better yield by heating
amidoazo toluenes with dilute nitric acid.
The researches of A. W. Hofmann, Witt, and Nietzki,
have determined the constitution of the Safranines, by
showing that they may be obtained :
(a) By heating Indamines with primary monamines ;
(6) By oxidising jp-diamidodiphenylamines in presence
of primary amines ;
(c) By oxidising a 2>ara-diamine in presence of m-
amido-diphenylamine ;
(d) By oxidising a mixture of one molecule of a para-
diamine and two molecules of a monamine, this being the
process used commercially. In this case the ^ara-diamine
should contain a free arnido-group, and the monamine
should be a primary amiiie, but two molecules of different
monamines may be used, in which case one of them
must be a primary amiiie. An Indamine is first formed :
260
ORGANIC DYESTUFFS
On oxidising in presence of a primary atnine, the
Indamiiie yields a Safnmine :
4- O.,
According to their method of formation, it would
appear that the Safranines are ^ara-quinonoid, but it
has been proved that there are two free amido-groups
in Phenosafranine, the simplest member of this class.
Hence the Safranines should be represented by orlho-
quinonoid formulae, thus :
N
NH
NH.,
01 C 6 H 5
Properties. The Safranines are very basic dyestuffs
which form three series of salts : the monoacid salts
are red and are not hydrolysed by water, whereas the
diacid and triacid salts, which are blue and green respec-
tively, only exist in concentrated acid solution. The
monoacid salts are well crystallised substances which
dye wool, silk, and tanned cotton red shades ; to some
QUINONE-IMIDE DYESTUFFS 261
extent they also dye cotton direct. Alkylation of the
amido-groups gives a more violet shade.
Phcnosafranine is prepared according to Witt by
oxidising a mixture of one molecule of p-phenylene-
diamine and two molecules of aniline, or by oxidising an
equimolecular mixture of ^-diamidodiphenylamine and
aniline. This mixture of the diamine and aniline
is obtained by diazotisiiig aniline in presence of an
insufficient amount of acid, and converting the diazo-
arnido benzene formed into amidoazobenzene by heating
with aniline hydrochloridc. On reduction of amidoazo-
benzene, it gives one molecule of ^-phenylenediamine
and one molecule of aniline :
C 6 H 5 N=N C 6 H 4 NH 2 + 4H
= C 6 H 5 NH 2 + NH a C 6 H 4 XH 2 .
A further molecule of aniline hydrochloride is added
to the solution, which is then oxidised with potassium
dichromate. In this reaction Mauvemes are formed
which are less basic than Safranine, and these are pre-
cipitated by addition of chalk. The filtered liquid
contains the Safranine, which is then isolated by salting
out with common salt. The hydrochloride crystallises
from dilute hydrochloric acid in green plates, which are
soluble in water to a red solution. The alcoholic
solution is fluorescent. The free base is obtained by
decomposing the sulphate by means of barium hydrate,
and crystallises in green plates.
Safranine readily gives a diazo-compound, and in
concentrated sulphuric acid solution will give a tetrazo-
compound. On boiling with alcohol, the diazo-com-
pound yields Aposafranine (Nietzki and Otto, Ber. y 1888,
21, 1730) :
Cl
262 ORGANIC DYESTUETS
the hydrochloride of which dissolves in water and
alcohol, giving red solutions, the alcoholic solution being
fluorescent. Under the same conditions, the tetrazo-
compound gives phenylphenazonium chloride, the parent
substance of the Safranines :
It is to be noted that in addition to symmetrical
Safranine, an asymmetrical isomer can exist :
ci
This compound has been prepared by Barbier and Sisley
(Bull. Soc. chim., 1905, 33, 995, 1190, 1232; 1906,
35, 1282) by oxidising a mixture of o-j?-diamidodi-
phenylamine and aniline. They have further shown
that this asymmetrical Safranine is formed together
with ordinary Safranine by the oxidation of a para-
diamine in presence of aniline, the two isomers* being
.separated by fractional crystallisation. To differentiate
between these two dyes tuffs they called the symmetric.*!,!
Safranines the Indoplienosafranines, and their isomers
the Azophenosafranines.
QUINONE-IMIDE DYESTUFFS 263
Dimethylphenosafranine is obtained by oxidising a
mixture of one molecule of dimethyl-p-phenylenediamine
and two molecules of aniline ; its zinc chloride compound
is known as Fuchsia or Methylene violet ; a higher
homologue, Giroflee or Tannin heliotrope is obtained
by condensing iiitrosodimethylaniJine with xylidine.
Tetraethylphenosafranine is prepared by oxidising an
equimolecular mixture of diethyl-^-phenylenediamine,
diethylaniline, and aniline. It is a violet dyestuff
known as Amethyst violet.
Safranine T is commercial Safranine or Tolusafranine,
and is generally prepared from a mixture of bases con-
taining a large amount of o-toluidine, such as Magenta
echappes. Its appearance and shade do not differ
appreciably from that of Phenosafranine, but the yield
obtained is much higher than with the simpler substance.
Magdala red is a Safranine of the naphthalene series,
and was obtained by Schiendl in 1868 by heat-
ing the hydrochloricle of a-amidoazonaphthalene with
a-naphthylamine. It is a basic red dyestuff which is
soluble in alcohol, forming a solution with a brilliant
yellow fluorescence.
Naphthyl violet and Naphlhyl blue are produced by
heat ing mtroso-/3-naphthylamine with the hydro chlorides
of a-naphthylamine and aniline. The commercial pro-
ducts are the sulphonic acids, which give fluorescent
shades on silk.
Basle blue is the basic dvcstuff obtained by condensing
nitrosodimethylaniline \\ith diphenyl-2 : 7 -naphthalene -
diamine. It may be dyed on tanned cotton.
Mauveines.
The Mauveines were the first synthetic dyestuffs
used in dyeing. In 1856, Perkin obtained Mauve me
by oxidising impure aniline ; it is a violet; dyestuff and
was used at that time for dyeing silk. Perkin described
two Mauveines, Pseudo-Mauveine, C M H 18 N 4 , prepared
264 ORGANIC DYESTUFFS
from pure aniline, and Mauveine G 27 H. 24 N 4 , obtained by
using a mixture of aniline and toluidine. As early as
1871 Hofmann and Geyger recognised the analogy
which exists between the Mauvcines and the Safranines.
The constitution of Psewrfo-Mauveine was established
synthetically by Nietzki by oxidising a mixture of
p-phenylenediamine and diphenyl-w-phenylenediamine :
C 6 H 5 Nil
C 6 H 5 NH
The Mauvemes are hence phenyl-derivatives of the
Safranines. They are less basic in character than the
Safranines, and are only of historical interest. For
many years one of these products was used for printing
the English penny stamp.
Indulines.
These dyes tuffs have been known since 1865, being
obtained by heating amidoazobenzene under pressure
with an aqueous solution of aniline hydro chloride.
Indulines are produced by heating aniline hydro-
chloride with amidoazobenzene, azobenzene, azoxy-
benzene, etc., more or less complex mixtures being
formed, according to the conditions of the reaction.
The Indulines which are soluble in water are the alkaline
salts of the sulphonic acids of the Indulines, which are
themselves insoluble in water, but are soluble in alcohol.
QUINONE-IMIDE DYESTUFFS 265
The Nigrosines are grey dyestuffs obtained by heating
aniline with nitrobenzene in presence of a little hydro-
chloric acid and iron at a temperature of 160 to 200.
Similar dyestuffs are obtained by heating aniline with
nitrophenol and aniline hydrochloride at 180 to 200.
Witt found that, by the action of aniline on amido-
azobenzene at a low temperature, there is formed
an intermediate product, azophenine, the constitution
of which was established by Fischer and Hepp as
diphenylamidoquinonedianilide :
NH
NH C 6 H 6
By raising the temperature to 125 to 130, Induline
3B is obtained, and, at 165 to 170, Induline 65.
The Indulines appear to be phenylamido-derivatives
of the Mauveines. They are used in the printing of
cotton in the form of a thickened mixture of the Induline,
tannin, and a solvent such as acetin (glyceryl acetate).
CHAPTER XXI.
INDIGO AND INDIGOID DYESTUFFS.
Historical. Indigo is one of the oldest dyestuffs
Known, being found on the wrappings of Egyptian
mummies. Originally it came from India ; Pliny and
DLs co rides mention unsuccessful attempts to acclimatise
it to European countries. After being forgotten for
many years, the Dutch imported the dyestuff from their
colonies of Batavia and Java in 1631. Indigo is also
found in a crucifera, the " dyer's woad " (Isatis tinctoria),
which was cultivated in France and in Germany as early
as the ninth century ; this culture was prosperous in
Thuringia in the sixteenth and seventeenth centuries.
This was used under t he name of Persian blue, and when
Indigo came from the East it encountered serious
difficulties. At first the use of Indigo for dyeing was
forbidden, and at Nuremberg the dyers were obliged to
take an oath not to use this " devil's colour " (Teufels-
farbe). It was only in 1737 that a royal edict in France
allowed the use of Indigo from the Indies ; from that
time its use extended to other countries, and finally the
culture of dyer's woad disappeared in spite of the aid
given to it by Napoleon I. The purple which was of
such great importance to the Romans, who extracted it
from a certain species of mollusc found on the shores
of Italy, has recently been shown by Friedliinder to be
i derivcitive of Indigo.
The commercial manufacture of Indigo by synthetic
methods was commenced about fifteen years ago, and
INDIGO AND INDIGOI1) DYESTUFFS 267
the artificial dyestuff has gradually replaced the natural
Indigo. This industry is restricted almost entirely to
Germany, where it is very prosperous, as shown by the
following statistics, relating to the value of imports and
exports of Indigo :
GERMANY.
IMPOKTS.
EXPORTS.
1895
21-5 million marks
1898
8*3 ,, ,,
7-6 million
marks
1904
21-7
5)
1906
0-8
31-6
J>
Towards the end of the year 1905, the production of
synthetic Indigo in Germany had reached three thousand
tons. This struggle between natural Indigo and the
synthetic product has caused a considerable decrease in
the price, which had fallen from seven to nine shillings
to three to four shillings a pound in 1908 (Nietzki,
Chemie der organ ische Farbtfoffe, 5th edition, p. 345).
Whereas the amount of Indigo exported by Germany
has increased rapidly, the culture of the plant in India
has decreased considerably. Thus, in the four provinces
which produce it, Bengal, Madras, Punjab and the
United Provinces, the area used for its culture from
1902 to 1907 amounted to 487,000 acres, in 1908-9 its
culture only occupied 283,900 acres (./. Soc. Chem. hid.,
1910, 14(>), and for the year 1910-11 only 263,700 acres.
It is estimated that at present the production of synthetic
Indigo has reached a value of three and a half million
sterling per annum, over 35,000 tons of 20 per cent, paste,
sold at sixpence per pound, being produced per annum.
Some 3,000 tons per annum are made in England.
K Detraction of Indigo. Indigo does not occur in the
state of ludigot ino in the plant from which it is extracted,
but is found as a compound which was first isolated by
Schunek, who termed it indican, and gave its formula
as C 28 H 31 17 N. It was supposed (and this view is still
268 OltUANIO DYESTUFFS
to be found even in many recent text-books) that
indican was a glucoside, resulting from the combination
of Indigo with a certaia sugar, indiglucine, this glucoside
being decomposed by dilute acids or ferments as follows :
2C 26 H 31 N0 17 +4H 2 =C 16 H 10 N a O, + 6C 6 H ]0 6 .
Indican. Iiidigotine. Indiglucino.
Marchlewski (J . Soc. CJiem. Ind., 1898, 430), however,
suggested that indican is the product obtained by con-
densing a molecule of indoxyl with glucose (see below),
according to which indican should decompose to give
these two constituents. This has actually been found
to occur by Hazewinkel, Beyerinck and van Romburg.
Moreover, HoogeweriT and Ter Meulen (Rec. trav. chim.
P.-B., 1900, 19, 106) have succeeded in isolating
indican in the form of a crystalline hydrate of formula :
C 14 H 17 N0 6 + 2H 2 0.
The extraction of the Indigo is carried out as follows :
The plants are cut down some time before flowering
and are placed in tanks or wooden vessels known as
"steeping vats." These arc then covered with boards
or bamboos on which are laid stones, and water added ;
a very vigorous fermentation occurs, lasting for twelve
to fifteen hours, during which time the indican is decom-
posed according to the following equation :
C 14 H 17 N0 6 + H 2 = C 6 H 12 6 + C 6 H 4 JdL
^ NH '
The indoxyl remains in the solution and gives it a
greenish yellow fluorescence. This solution is drawn
off into larger vats, in which it is exposed by some
mechanical means to the action of air. The air oxidises
the indoxyl, and then the leuco-Indigo gives Indigotine,
which is precipitated in fluorescent blue pariieleH. After
standing for several hours, the supernatant liquid is
decanted, the precipitate boiled with water to prevent
INDIGO AND INDIGOID DYESTUFFS 269
destructive fermentation, and the dycstuff is filtered off.
The mass obtained is eompressed and broken into
lumps which are then dried. The yield of Indigo is
about 0-2 per cent, of the weight of the plants used,
the average yield being 2,500 to 3,000 kilograms of the
plant per acre of ground. The Indigo obtained is,
however, often very impure^, containing 20 to 90 per
cent, of Indigotine in addition to a red dyestuff known
as Indirubine, Indigo yellow, Indigo brown, Indigo
gluten, mineral matter, etc. Occasionally it has to
be purified to increase its value. Chemically pure
Indigotine is very difficult to obtain ; after repeated
purification by chemical means it is often necessary to
sublime it in vacuo.
Properties of Indigotine. This compound is obtained
as an amorphous powder which has a copper reflex when
it is compressed. It crystallises from acetic acid,
phthalic anhydride, nitrobenzene, aniline, or phenol,
and also sublimes, forming crystals with a brilliant
metallic lustre. On heating it forms violet vapours, and
at a high temperature decomposes. It dissolves in cold
sulphuric acid to form a green solution, addition of water
precipitating the dyestuff unchanged ; on heating
the sulphuric acid solution, it becomes blue and the
substance remains in solution on diluting, owing to the
formation of sulphoriic acids. According to the condi-
tions, mono-, di- ; tri- or tetra-sulphonic aeids are obtained ;
the sodium salt of the disulphonic aeid is known as
Indigo carmine. Oxidising agents destroy Indigotine,
giving isatin.
The most interesting property is its conversion by
alkaline reducing agents to leuco-Indigo (Indigo white),
which dissolves, forming a yellow solution. This
solution oxidises in contact with air, regenerating
Indigotine. This property is applied in the dyeing of
textile fabrics, a solution of the reduced Indigo, known as
an " Indigo vat," being prepared, and the fibre immersed
in it ; after being squeezed the fibre is exposed to air
270 ORGANIC DYESTUFFS
to regenerate the dyestuff. The reducing agents in
general use are : ferrous sulphate and lime ; zinc and
an alkali ; glucose and caustic soda ; and sodium
hydrosulphite. The people of the East, who were able
to dye with Indigo more than five thousand years ago,
used vats obtained by fermentation as described above,
these being still employed in certain countries. In these
vats the reduction is effected by the fermentation of
various organic substances, such as bran, glucose, faeces,
etc. The reduction of Indigo is assisted by the presence
of a small quantity of Induline scarlet (B.A.S.F., E.P.
29,918 (1910) ).
Kalb (Ber., 1909, 42, 3642) suggests a new method in
which dehydroindigo, obtained by oxidising Indigo with
lead dioxide in non-aqueous suspension, is used :
It forms stable, crystalline, bisulphite compounds, with
which the fibre is padded, dried, and then passed into an
acid or alkaline bath at 80-100 C. to regenerate Indigo.
Constitution of Indigotine. The percentage com-
position of Indigotine corresponds to the formula
C 8 H 5 ON, but determination of its molecular weight gives
the formula C 16 H 10 2 N 2 , and in certain solvents the
cryoscopic method gives values corresponding to double
this formula (Sommaragu, Ann., 1879, 195, 312 ; Vaubcl,
Zeitsch.f. Farben- u. Textil-Chem., 1902, 1, 39).
Oxidation with chromic acid decomposes Indigotine,
giving two molecules of isatin :
C 16 H 10 2 N 2 + 2 = 2C 8 H B 2 N,
showing that the Indigotine molecule is symmetrical
and formed from two C 8 H 6 ON groups linked together.
Isatin is hence derived directly from the complex
C 8 H 5 ON, and if the constitution of this group of atoms
is determined, that of Indigotine may easily be deduced.
On reduction, under different conditions, isatin yields
INDIGO AND INDIGOID DYESTUFFS 271
three products (Baeyer and Knopp. Ann., 1808, 140, 295):
dioxiiidol, C 8 H 7 O 2 N ; oxiiidol, C 8 H 7 ON ; and indol,
C 8 H 7 N. Indol may also be obtained directly by reduc-
tion of Indigo tine, which it regenerates to some extent
on oxidising with ozone (Nencki, Ber., 1876, 9, 299).
This was one of the first syntheses of Indigo, Nencki
having extracted indol from the products obtained by
the pancreatic digestion of albumen (Ber., 1874, 7, 1593).
Hence, indol may be regarded as the parent substance
of isatin and of Indigotlne, the manner in which the
atoms are arranged being the same in these various
compounds. The dry distillation of Indigotine gives
aniline, whilst in the products obtained by the alkaline
fusion of Indigotine or isatin is found o-amidobenzoic
acid. Hence, these substances (Indigotine, isatin and
indol) contain the same grouping, namely, a benzene
nucleus in which one of the carbon atoms is bound to
nitrogen ; the formation of o-amidobenzoic acid shows
that there is also a carbon atom attached to the nucleus
in orJ/w-position to the nitrogen atom. Indol contains
the grouping, C 7 H 4 N :
OH
^ \
HC C Cs
I II
HC C N -
\ /
CH
To this grouping CH 3 must be added to give indol.
Indol is a weak base, but does not contain an ainido-
group. It gives a nitroso -compound and an acetyl
compound. These properties would agree with those
of a compound containing the imido-group, NH, and
indicates the following constitution I
CH
C 6 H
NH
272 ORGANIC DYESTUFFS
This has been proved by the synthesis of indol. Baeyer
and Eminerling (Ber., 1869, 2, 680) obtained indol by
fusing o-nitroeinnamic acid with caustic potash and
iron filings. Baeyer and Caro (Ber., 1877, 10, 692, 1262)
observed the formation of indol on passing the vapours
qf diethyl-0-toluidine through a red-hot tube.
The constitutions of isatin and oxindol have been
established by their synthesis. Oxindol is the internal
anhydride of o-amidophenylacetic acid (Baeyer and
Knopp, loc. cit.) :
CH 2 COOH CH 2
NH 2 NH
and isatin is the internal anhydride of o-amidophenyl-
glyoxylic acid (Claisen and Shadwell, Ber., 1879, 12, 350) :
CH COOH CO
NH 2 NH
Isatin has the property of reacting in either of two
tautomeric. forms, either as a lactam, known as pseudo-
isatin, or as the lactim, for which the name isatin is
reserved : these two forms have not been isolated in the
free state, but Pummerer (Ber., 1911, 44, 338) has
recently prepared certain of their derivatives.
CO CO CO
C 6 H C.OH C 6 H 4 X) C 6 H
N NH N
Isatin. Pseudo- Isatin. Isatin Chloride.
With phosphorus pentachloride, a chloride is obtained
which is a derivative of isatin. Comparing the mole-
cular formula of this chloride, C 8 H 4 ONC1, with that of
Indigotine (C 8 H 5 ON) 2 , it will be seen that they differ
INDIGO AND INDIGOID DYESTUFFS 273
by the substitution of 01 for H. By eliminating the
chlorine and replacing it by hydrogen, Indigotine should
be obtained. Baeyer (Ber., 1879, 12, 456) has actually
obtained Indigo by reducing isatin chloride with zinc,
and hence Indigotine results from the combination of
two groupings of the formula :
[
CO
O.H 4X /
N
It only remains to determine exactly how this com-
bination occurs. On boiling o-nitropheiiylpropiolic acid
with water, it loses carbon dioxide, and gives ortho-
nitrophenylacetylene. On oxidising with potassium
ferricyanide two molecules combine, giving di-o-nitro-
phenyldiacetylene :
c=c c=c
C 6 H 4 <( NC^
NO 2 N0 2
On treating this compound with sulphuric acid and
reducing with ammonium sulphide, Indigotine is pro-
duced (Baeyer, 7?er., 1882, 15, 50). This synthesis shows
that the two benzene rings in Indigotine are linked
together by a chain of four carbon atoms. Hence on
reduction of isatin chloride, combination must occur by
the linking of the carbon atoms adjacent to nitrogen, thus
establishing the constitution of Indigotine, as follows :
CO
2C 6 H 4 / \C-C1 + 4H = 2HC1 +
N
CO CO
cH 4 / )>c = c/ ;c 6 H 4
NH NH
Q.D. S
274 ORGANIC DYESTUFFS
This formula also explains its properties. Thus
oxidation yields two molecules of isatin :
CO CO
C 6 H 4 / ^C = C/ \C 6 H 4 + 2
NH NH
CO
= 2 C 6 H^ \CO
NH
Reduction gives fewco-Indigo (Indigo white), which is
soluble in alkalies, due to the presence of hydroxyl
groups :
C 6 H 4 / C = C C 6 H 4 + H
2
C 6 H 4 C-C . >C 6 H 4
\ NH / \ NH /
Binz an^Walter (Zeitschr. angew. Chem., 1906, 19,
1415) showed that the formation of an Indigo vat, using
caustic soda and sodium hydrosulphite, depends upon the
sodium salt of Indigo first produced passing into solution
owing to the loss of two hydroxyl groups. This is
represented by the following equations :
X NH X /NH,
C 6 H 4 < >C = C< >C 6 H 4 + 2NaOH
NH,
64 = \C 6 H 4 + Na 2 S 2 4
OH ONa OH ONa
/NH, /Ntt.
C 6 H 4 / /C-C;/ ^C.H, + 2NaHS0 3 .
ONa ONa
INDIGO AND INDIGOID DYESTUFFS 275
On reoxidising, which only takes place in presence
of moisture, caustic soda is produced, leaving Indigotine
on the fibre. Other reactions accompany this oxidation
(see Crowther, J. Sac. Dyers and CoL, 1911, 27, 146;
also Ehrhardt, ibid., 1913, 29, 121). Binz and Sehadel
(Ber., 1912, 45, 586) have obtained further evidence that
the formation of the Indigo vat is due to removal of
oxygen, and not to addition of hydrogen. Liebermann
had previously found that on acetylation, Indigo white
behaved as though it possessed the formula :
7X XX
C 6 H/ >C-C< >C 6 H 4 ,
MXK I |\CO/
H H
and hence exists in two tautomeric forms.
The constitution of isatin accounts for its conversion
into dioxindol and oxindol by reducing agents.
Indoxyl is an isomer of oxindol and is found in the
urine of herbivorous animals in the form of its sulphuric
ester (Baumann and Tiemann, Ber., 1879, 12, 1192 ;
1880, 13, 415) ; it was synthesised by Baeyer (Ber., 1881,
14, 1741) by reducing o-nitrophenylpropiolic acid with
ammonium sulphide, when the indoxylic acid first
produced loses carbon dioxide, giving indoxyl ;
C 6 H 4 < >C-COOH = CO 8
NH
/C(OHU
C 6 H 4 < >
or C 6 H 4
NH /
(I.) (II.)
Indoxyl can also react in either of two tautomeric
forms, which are called indoxyl (I.) and pseudo-indoxyl
(II.). It has been obtained in the pure state by Vor-
lander (Ber., 1902, 35, 1701) in the form of yellow crystals.
Indoxyl oxidises rapidly on exposure to air, giving
276 ORGANIC DYESTUFFS
liidigotiiie. It condenses with aldehydes and with
ketones to give the indogenides (Baeyer, Ber., 1882, 16,
2197 ; Nolting, Bull Soc. chim., 1902, 27, 835) ; thus
with isatin it yields the indogenide Indirubine, a red
dyestuff which is an isomer of Indigotine, with which
it occurs in natural Indigo, and which has the following
constitution :
/C(X ......................... / co \
C C H 4 < >C:H 2 + OC< >NH
' ........
/ co
= C 6 H 4 < >C-C< >NH + H 9 0.
\NH/ X C 6 H/
This constitution, which was established by Baeyer,
has recently been further proved by Wahl and Bagard
(Bull. Soc. cliim., 1909, 5, 1041), who have syiithesisecl
Indirubine by condensing isatin chloride with oxindol.
In addition to Baeyer's indogenides, Wahl and Bagard
have prepared a series of the isomeric compounds, the
iso-indogenides, from oxindol. The t'soindogenide of
isatin is a further isomer of Indigotine :
/CO, ,,CH,
C 6 H 4 < >CO + CO<
CO
to which these authors have given the name iso-Indi-
gotine ; it crystallises in garnet coloured needles which
are insoluble in alkaline reducing agents.
SYNTHESES OF INDIQOTINE.
In the preceding port ion it has been seen that Indigotine
may be synthesised by various methods : by the oxidation
of indol by ozone (Nencki in 1875) ; the synthesis of
INDIGO AND INDIGOID DYESTUFFS 277
oxindol and its conversion into isatin (Baeyer and Comm-
stock, Ber., 1883, 16, 1704) ; the synthesis of isatin and
isatin chloride, the reduction of which gives a mixture
of Indigotine and Indirubine (1879). It was not,
however, until the year 1882 that Baeyer and Drewsen's
synthesis from o-nitrobenzaldehyde gave a process with
some possibility of commercial application. Even this
possibility was not quickly realised, as attempts to
carry out the process on a large scale failed for a long time.
In his address to the German Chemical Society (March,
1910), B. Bohn remarked that " The historian will not
be able to pass over in silence the period of deep depression
which was produced by difficulties encountered in all
the various attempts made to apply the results of
Bacyer's researches in commerce. New dyestuffs were
then sought to replace Indigo."
With the synthesis of Heumann (Bcr., 1890, 23, 3044,
3431 ; D.R.P. 54,626 and 56,273 (1890) ), using phenyl-
glycine and its carboxylic acid, a new method was
available to investigators which finally solved the problem
of the manufacture of Indigo, one of the most striking
chemical syntheses.
The various synthetic processes will be described in
the following order :
I. Syntheses from cinnamic acid.
II. Syntheses from o-nitrobenzaldehyde.
III. Syntheses from thiodiphenylurea and nitroso-
ethyldiphenylamidine (Sandmeyer's synthesis).
IV. Syntheses from phenylglycine.
V. Syntheses from anthranilic acid.
I. Syntheses from Cinnamic Acid
The nitration of cinnamic acid or its esters yields a
mixture of isomerides, of which only the o-nitrocinnamic
acid can be converted into Indigotine, this being carried
278 ORGANIC DYESTVFFS
out in several ways. On treating with bromine and
then with alcoholic potash, this compound gives o-nilro-
phenylpropiolic acid :
/CH-CHCOOH
C,H/ + Br 2 >
X N0 2
/CHBr CHBr COOH
C,H/ + 2KOH
X N0 2
,C==C COOH
= C 6 H 4 < + 2KBr + 2H 2 0.
The action of reducing agents (glucose and caustic
soda, or alkali xanthates) converts this acid into
Indigotine ; the yield is about 70 per cent, and the pro-
cess was used for some time in calico-printing (D.R.P.
15,516). It has already been shown that this acid may
also be converted into nitrophenylacetylene. Finally,
onitrocinnamic acid combines with a molecule of
hypochlorous acid, giving o-nitrophenylchlorlactic acid,
which on treatment with alkalies loses hydrochloric acid
to give o-nitrophenyloxyacrylic acid :
O
C.H
N0
This compound gives Indigotine on fusing or heating
with acetic acid or phenol (D.R.P. 11,857 (1880) ).
II Syntheses from o-Nitrobenzaldehyde.
In 1882, Baeyer and Drewsen (Ber., 1882, 15, 2856)
showed that an excellent yield of Indigotine was obtained
by treating o-nitrobenzaldehyde dissolved in acetone
INDIGO AND INDIGOID DYESTUFFS 279
with caustic soda. Aldol condensation first takes place,
and then acetic acid and water are split off :
X CHO
C 6 H 4 < + CH 3 CO CH 3
X N0 2 .
yCHOH CH 2 CO CH 3
P TT / 2 3
^6^4^
X N0 2
or CH(OH) CH CO CH 3
/ / co \ \
= CH 3 COOH + H 2 O + C 6 H 4 < >C =
\ X NH/ /
Two of the groupings so obtained then combine to give
Indigo tine.
The acetone may be replaced by acetaldehyde or by
pyruvic acid (Baeyer and Drewsen, Her., 1883, 16,
2205; D.R.P. 19,768) ; moreover, by using a substituted
o-nitrobenzaldehyde, a substituted Indigo is readily
obtained. Thus, o-nitro-m-toluic aldehyde (Hochst
Farbwerke, D.R.P. 21,683), chlor- and brom-o-nitro-
benzaldehyde (D.R.P. 30,339), and dichlor-o-nitro-
benzaldehyde (D.R.P. 32,238) have been used.
" Indigo salt," used to some extent in printing, is
formed by combining the above alcohol (o-nitropheriyl-
lactylketone) with sodium bisulphite ; it is a white
substance which is stable in air, but yields Indigo with
alkalies.
Syntheses by means of o-nitrobenzaldehyde are,
however, dependent on the preparation of this com-
pound, which is rather difficult. The nitration of
benzaldehyde only gives a small amount of the ortho-
compound, yielding 100 to 105 per cent, of its weight of
the ^p-nitro-derivative and only 20 to 25 per cent, of
280 ORGANIC DYESTUFFS
the or^o-derivative. By treating o-nitrotoluene with
chlorine under certain conditions, it is partly converted
into o-nitrobenzyl chloride, and this compound may be
converted into the aldehyde by several processes. Thus
on heating with alkali salts, acetates, sulphites, or
thiosulphates, it is converted into the corresponding
esters of o-nitrobenzyl alcohol, which are then oxidised
(D.R.P. 48,722, 104,360) :
/CH 2 01
C 6 H 4 < + NaOOC.CH,
X N0 2
/CH 2 O(COCH 3 )
- C 6 H 4 < + NaCl .
X NO 2
or the product may be heated with aniline, the benzyl-
aniline oxidised, and then the benzylidcne aniline so
obtained hydrolysed (Hochst Farbwerke, D.R.P. 91,503,
92,084, 93,539, 97,847, 97,948) :
/CH 2 C1 /CH 2 NH C 6 H 6
C 6 H 4 <( + NH 2 -C 6 H 5 = C 6 H/ HC1
X NO 2 X N0 2 +no1
/CH 2 NH C 6 H 5
C.H/ +
X NO 2
/ CH=N-C 6 H 5
= C 6 H 4 < +H 2
X N0 2
Finally, the side chain of hydrocarbons has been
converted into the aldehyde group ; thus, on oxidising
o-nitrotoluene with manganese dioxide in presence of
sulphuric acid :
/CHo /CKO
C 6 H 4 < +0 2 = C 6 H 4 < +H 2
Other methods are known, but they are of less
importance.
INDIGO AND INDIGOID DYESTUFFS 281
III Sandmeyer's Syntheses.
These were discovered by Sandmeyer at the works
of Geigy and Co. in Basle in 1899. There are two
processes :
(1) By the action of chloral on a mixture of aniline
and hydroxylamine hydrochlorides, an isonitroso- deriva-
tive is obtained :
. .. . /{-Sl JHLnjN OcJLLc
C 6 H 5 NHiH + Cl: C< +
| X C1
CH O H,N OH
C 6 H 5 NH C =N C 6 H 5
= I + 3HC1 + H 2 O
CH=N OH
On heating with sulphuric acid, this compound loses
ammonia, giving isatin a-anilide :
CH=NOH
/1 vr /~i TT
NH
C=N-C 6 H 5 4- NH 3
NH'
and this compound is readily and quantitatively con-
verted by means of reducing agents, such as ammonium
sulphide, into Indigotine.
(2) Carbon disulphide gives symmetrical diphenyl-
thiourea with aniline, from which lead salts remove sul-
phuretted hydrogen :
/NH C 6 H 5 Jtf-C 6 H 5
CS< - CC + H 2 S
\NH C 6 H 8 ^N C 6 H 6
282 ORGANIC DYESTUJPPS
On treating this compound with potassium cyanide,
hydrocyanocarbodiphenylimide is produced :
,N-C 6 H 5 ^N-C 6 H 5
Cf + HCN = C
NH-C 6 H 5
This product is also formed by dehydrating the above
isonitroso-compound, and is readily converted into the
anilide obtained in (I.) by treating with ammonium
sulphide and then with concentrated sulphuric acid.
The following thioamide is formed as an intermediate
product :
OS NH,
IV. Syntheses from Phenylglycine.
In 1890 Heumanri (Ber., 1893/26, 225; D.R.P. 54,626
and 54,988) showed that the product obtained by the
alkaline fusion of phenylglycine yielded a small amount
of Indigotine on oxidation in air. It may be supposed
to be formed from indoxyl according to the equation :
/ co \
C a H 5 . NH CH 2 COOH = C 6 H 4 < ^CH. + H 2 0.
Phenylglycine is obtained by condensing aniline with
monochloracetic acid :
C 6 H 5 NH 2 +C1CH 2 COOH = HC1 + C 6 H 5 NH-CH 2 COOH
or by the action of a mixture of formaldehyde and potas-
sium cyanide on aniline (Deutsche Gold- und Silberscheide
Anstalt, D.R.P. 117,623, 137,955, 141,749) :
C 6 H 5 NH a + CH 2 O + HCN = C H 5 NH CH 2 CN
v C 6 H 5 NH CH 2 COOH.
INDIGO AND INDIGOID DYESTUFFS 283
This preparation has been the subject of a number of
patents (Bucherer, D.R.P. 157,710, 157,909, 157,910 ;
B.A.S.F., D.R.P. 156,760, 157,617, 158,346, 158,090,
158,718, 181,723).
The alkaline fusion of phenylglycine only gives a very
small yield of Indigotine, owing to decomposition
occurring at the high temperature (300) at which the
reaction must be carried out. Jlence an attempt has been
made to replace caustic alkalies by mixtures, in order to
lower the temperature of reaction to about 200 ; thus, by
mixing phenylglycine with a mixture of alkalies and
sodium peroxide, sodium ethylate, lime, etc., greater
yields are generally obtained. In 1900 it was found that
sodamide was a very suitable reagent for converting
phenylglycine into Indigotine (Deutsche Gold- u. Silber-
scheide Anstalt, D.R.P. 169,186). This process has
been used by the Hochst Farbwerke, and gives good
results (see p. 286).
V. Syntheses from Anthranilic Acid.
Heumann noticed that Indigotine is also formed
by the alkaline fusion of phenylgtycine o-carboxylic
acid. In this reaction the yield is considerably greater
than that obtained with phenylglycine under the
same conditions, and this method became the com-
mercial process as soon as phenylglycine o-carboxylic
acid could be satisfactorily obtained. The commercial
prepni tition of this acid, and hence of Indigo, was first
carried out by the B.A.S.F., who have devoted a large
amount of capital to the installation of the necessary
plant.
The raw material is naphthalene, which is first con-
verted into phthalic acid by oxidation ; the most
suitable oxidising agent is fuming sulphuric acid, the
action of which is made more energetic by the addition
of mercury salts :
284 ORGANIC DYEb'TUFFS
CH CH CH COOH
//'\ C / /X \
HC / \ x v CH HC
HC
CH
CH CH CH COOH
This reaction is carried out at about 280-300.
Phthalic acid, or better, i\& anhydride, is then converted
into phthalimide by heating to 225 with ammonium
carbonate, or by passing ammonia into fused phthalic
anhydride :
/ co \ / co \
C 6 H 4 / \0 + NH 3 = H 2 + C 6 H 5 <(^ \NH
The phthalimide is then treated with alkaline hypo-
chlo rites (Hofm ami's reaction), and gives anthranilic
acid, intermediate compounds probably being produced
as follows :
CO /COx C0
C 6 H 4 NH->C 6 H 4 / N-C1 -C 6
co x co COOH
,NH COOH ,NH 2
* C 6 H 4 <^ > C 6 H 4 /
X COOH \COOH
The conversion of anthranilic acid into phenylglyeine
o-carboxylic acid can be carried out in several ways.
Thus anthranilic acid may be treated with mono-
chloracetic acid. The reaction must be carried out at
a low temperature (40), being then very slow ; at
higher temperatures secondary products are obtained.
C 6 H 4 < +C1CH 2 COOH
\COOH
/NH CH 2 COOH
= C 6 H 4 < + HC1
X COOH
INDIGO AND INDIGOID DYESTUFFS 285
By the action of a mixture of formaldehyde, sodium
bisulphite and potassium cyanide on anthranilic acid
in aqueous solution, the following changes occur rapidly,
giving an excellent yield :
/NH CH 2 SO 3 H /NH CH 2 CN
C 6 H 4\ . -- > C 6 H 4\
X COOH X COOH
X NH CH 2 COOH
> C 6 H 4 <^
X COOH
This acid is then fused with an alkali, the resulting
mass dissolved in water and oxidised by a current of air :
NH
OH/ \
6 M 4\ CH 2 COOH = H 2 +
COOH
NH
C 6 H/ ^CH COOH -- * Indigotine.
Synthetic Indigotine contains impurities which may
be removed by various methods, such as boiling with
pyridine. Indigo comes into commerce in the form of a
paste or an impalpable powder.
Sandmeyer's syntheses have not yet received practical
application, as the works at which this process was
attempted (Geigy and Co., Basle) were destroyed by
fire some years ago. This process has been perfected
by Rahtjen, and a company has been formed at Ham-
burg, with a capital of a quarter of a million sterling, with
a view to its exploitation (Ohem.-Ztg., 1910, 162).
Syntheses from o-nitrobenzaldehyde are dependent
on toluene as the raw material, and the production
of this substance is somewhat limited. It has been
calculated that four tons of this hydrocarbon yield
one ton of Indigo, and as the monthly consumption
286 ORGANIC DYESTUPFS
of Indigo is seven to eight thousand tons, this would
require thirty thousand tons of toluene. Hence the
production of toluene is not sufficient under present
conditions, although the increasing use of bye-product
coke-ovens will naturally lead to an increase in the
production.
Syntheses from phenylglycine or its carboxylic acid
require as raw materials aniline, naphthalene, and
monochloracetic acid. The electrolytic soda industry
yields the necessary amount of chlorine for the ready
preparation of monochloracetic acid. Naphthalene is
the commonest of the hydrocarbons ; according to
Brunck, its production amounts to forty or fifty thousand
tons per annum, and its price is about 4 per ton. Its
conversion into phthalic anhydride can be carried out
very economically, as the catalytic process yields fuming
sulphuric acid at a very low price. The Badische Co.
manufactures its Indigo Pure B.A.S.F. in a works
which cost over a million sterling to erect.
Of the numerous syntheses of Indigotine which have
been suggested or actually carried out on a large scale,
the sodamide modification of Heumann's process is the
chief one. This great improvement over the original
caustic fusion was the invention of the Deutsche Gold
und Silberscheide Anstalt, and was acquired by Meister,
Lucius and Briming. The yield of the alkaline fusion
method was 13 per cent., whereas it is stated that the
sodamide process gives over 75 per cent, of the theoretical
amount. To avoid handling sodamide as such, it is
probable that ammonia gas is passed over a mixture of
phenylglycine, caustic alkali, and sodium, sodamide
being thereby formed in situ.
The leuco-compound, Indigo white, is now com-
mercial, various patents having been taken out of
methods used to increase its stability, and at the same
time to facilitate its solution or the ease of obtaining
a vat. (For details see Vlies, J. Soc. Dyers and Col.,
1914, 22.)
INDIGO AND INDIGOID DYESTUFFS 287
Indirubine.
This compound is the isomer of Indigotine, together
with which it occurs in almost all the natural products,
particularly in Indigo from Java, which frequently
contains 5 to 7 per cent, of Indirubine, from which
Indigo from India is practically free (see A. G. Perkin,
J. Soc. Dyers and Col., 1911, 52). Its constitution was
established by Baeyer (Ber., 1881, 14, 1745), who syn-
thesised it from isatin and indoxyl. Another synthesis
has recently been carried out by Wahl and Bagard (Bull.
Soc. diim. y 1910, 7, 1090 ; 1911, 9, 56) by condensing
isatin chloride with oxindol, thus :
C 6 H >CO + Cl-C >C 6 H 4
/ /^
= C 6 H / CO CO^ ^N + HC1
which passes into the isomeric compound Indirubine :
/CO . / CO ,
NH< >C=C< >C 6 H 4
This reaction may be applied to substituted deriva-
tives of isatin, which yield, on condensation with oxindol,
substituted derivatives of Indirubine of the type :
NH C = C >C 6 H 3 X
CO
X3,H
The same derivatives may be obtained by condensing
isatin with substituted derivatives of indoxyl, X being
Br, 01, NO 2 , etc.
288 ORGANIC DYESTUFFP
Action of Alkalies on Indigotine and on Indirubine.
Warm concentrated alkalies decompose Indigotine,
giving an orange solution from which acids precipitate
chrysanilic acid. Friedlander and Schwenk (Ber., 1910,
43, 1971) have shown that this acid is not the first
product formed, indoxyl-2-aldehyde and anthranilic
acid being first produced, thus :
/CO, /CO.
C 6 H 4 < >C=C/ >C 6 H 4
x CO x | , 0(ONa)v
C 6 H/ >C-C^ >C 6 H 4
/ \ /
OH
|
>C
/COOH
-* C 6 H 4 < + CHO-C >C 6 H 4
X NH 2 \ NH /
Unless the indoxyl-2-aldehyde is removed by ether,
these products condense on acidifying to give chrysanilic
acid.
Under the same conditions, Indirubine yields an
isomeric aldehyde, oxindol-3-aldehyde, as follows :
7 co x / ccf x
C 6 H/ >C = C< >NH
X NH X X C 6 H/
OH
C 6 H 4 -C )NH
C 6 H 4 /
/COOH ^
C 6 H 4 ( + CHO Of >NH
. N C 6 H 4
This reaction occurs with all the Indigoid dyestuft's, and
also with derivatives of Thioindigo. Thus Thioindigo
scarlet R yields chrysanilic acid and thiosalicylic acid,
INDIGO AND INDIGOID DYESTUFFS 289
INDIGOID DYESTUFFS.
For a long time Indigo and Indirubine occupied an
isolated position amongst the organic dyestuffs. Fried-
lander (for nomenclature of the Indigoid compounds
see Friedlander, Monatsh. f. Chem., 1898, 29, 359) has
shown that there exists a class of dyestuffs which he
terms " Indigoid " dyestuffs, of which Indigo and
Indirubine only constitute the first members. The
Indigoid dyestuffs are characterised by the presence of
the grouping :
CO C-C CO
I I
which occurs in Indigotine and its two isomers, Indi-
rubine and iso-Indigotine. Indigoid dyestuffs may be
symmetrical or asymmetrical according to whether the
two parts of the molecule united by the double bond are
identical and apparently similarly arranged, or whether
they are different in structure or orientation.
The symmetrical dyestuffs are obtained by oxidising
products similar to indoxyl, and have the constitution :
in which X represents a divalent atom or group, such
as O, CO, S, NH, CO . NH, etc. ; the group C 6 H 4 may
itself be replaced by another ring. The asymmetrical
dyestuffs are prepared by condensing a compound similar
to indoxyl with a cyclic ketone such as isatin, thus :
- XXX / CO \
C 6 H 4 < >C|H 2 "T'"OiC< >Y
\/ ............................ X
/CO. /CO.
= C 6 H/ )> C = C \ /> Y + H 2
-X- OftH^
O.D.
290 ORGANIC i DYESTUFFS
They are also obtained by condensing isalin chloride
or isatin ajiilides with cyclic molecules containing a
C(OH)=CH group, such as phenols, diphenols, naph-
thols, pyrazolones, isoxazolones, pyramidines, etc.
(Friedlander, Ber., 1908, 41 ? 772 ; Friedlander, Bezdrik,
and Koniger, ibid., 227). It will hence be seen that
a large variety of Indigoid dyes tuffs can be obtained,
some of which have already met with great commercial
success.
Thioindigo.
The preparation of this dyestuff is very similar to
the synthesis of Indigo tine from anthranilic acid (Kalle,
D.R.P. 188,702, 192,075, 194,237, 194,254, 177,346
(1905). For further details see J. Soc. Chem. Ind., 1909,
32, 565). It consists in fusing pheiiylthioglycine-o-
carboxylic acid with alkalies and oxidising the aqueous
solution of the resulting product, by means of a current
of air, or other oxidising agent, such as dichromate,
ferric chloride, etc.
XX)OH
C 6 H/ .CH 2 COOH = H,0 + C0 2 +
\S-^
/ C0 \
C 6 H/ >CH 2 or CeH^
\s / \ s /
There is produced a compound which differs from indoxyl
by the replacement of the NH group by S, and is called
thioindoxyl or 3-oxythionaphthen.* Like indoxyl, this
is oxidised on exposure to air, giving the dyestuff.
CHCH
*Thiophen has the constitution : \\ \\ and hence the name
cy
thionaphthen has been given to the compound :
INDIGO AND INDIGOID DYESTUFFS 291
The raw material for this process, phenylthioglycine-
o-carboxylic acid, may be obtained in several ways ;
thus, if anthranilic acid is diazotised %and treated
with a solution of sodium disulphide, obtained by
dissolving sulphur in sodium sulphide, the following
reaction occurs :
N =N 01
=
2C 6 H 4 < + Na 2 S 2 = 2NaCl
XX)OH
X N=N S S N=N X
C 6 H/ >C 6 H 4
\COOH COOH/
The diazodisulphide produced is very unstable, and
loses its nitrogen, giving dithiosalicylic acid, which is
converted by reducing agents into thiosalicylic acid :
C 6 H 4 + H 2 = 2C 6 H 4 <
COOH COOH \COOH
Finally, by the action of monochloracetic acid on this
acid, phenylthioglycine-o-carBoxylic acid is obtained.
Diazoanthranilic acid may also be combined with
thioglycine, obtained by treating monochloracetic acid
with sodium sulphide :
X COOH
f Cl
xCOOH
C 6 H 4 < + HS CH 2 COOH
NM^T- ~
+ HC1
-N =N S CH 2 COOH
This diazosulphide also readily loses its nitrogen and
yields the acid required.
Of the numerous processes for the preparation of
Thioindigo which have been made the subject of
292 ORGANIC DYESTUFFS
patents may be mentioned the process which consists
in condensing acetylene dichloridc with thiosalicylic
acid and dehydrating the compound formed (Munch,
Zeitsch. angew. Ghent., 1908, 21, 20.TO ; D.R.P. 205,324) :
SH SH X
C G H/ + Cl CH=CII Cl + X H 4
HX)OH COOH/
:=CH s v
C.H 4< >C 6 H 4
X COOH COOH/
/ S \ ' / S
The commercial product Thioindiyo (red) B, which is
prepared by the firm of Kallo according to Friedlander'y
patents, dyes cotton from a vat, giving fairly fast violet
red shades. (See Knccht, J. Soc. Dyers and Col.,
1906, 50.)
Thioindigo scarlet R (Kallo, D.R.P. 187,586, 190,292,
182,260, 193,150) is the dycstuff obtained by condensing
isatin with oxythionaphthen :
C 6 H >CH 2 +CO/ NH
co
\CH
6
= C 6 H 4 < >C = C< >NI-1 + H a O
Its constitution is determined by its method of formation.
It dyes cotton brilliant scarlet shades.
INDIGO AND INDIGOID DYESTUFFS 293
Substituted Indigoid Dyestuffs.
Ciba Dyestuffs (Soc. pour rind, chim., Basic, D.It. P.
190,292, 192,682, 193,438). These dyestuffs are poly-
halogenated derivatives of the Indigoid dyestuffs,
Incligotine, Indirubine, Thioinrligo, Thioindigo scarlet,
etc., produced by halogcnation at high temperatures
in absence of water, using nitrobenzene, dichlor benzene,
glacial acetic acid, etc., as solvents (E.P. 5122, 6105,
9546, and 13,148 (1907) ; 19,563 (1908) ). The original
name is now used as a trade name for all the Indigo
derivatives of this firm. Whereas the mono- and cli-
halogenated derivatives are only of slight importance,
the tri- and tetra-halogenated derivatives have very
pure shades which differ from those of the original
substances. The position of the substituted atoms has
a great influence on the shade produced. Ciba blue B
and 2B are tri- and tetra-brom-Indigotine.
On heating Indigo with an excess of benzoyl chloride,
dibenzoyl -Indigo, a brown amorphous powder of M.P, 108,
is produced. In presence of condensing agents, such as
copper, using nitrobenzene as solvent, an intense yellow
dyestuff is produced (Engi and Frohlich, U.S.A. Pat.,
1026,574 (1912) ), Indigo yellow 3 Ciba, which probably
has the following composition :
/ca /co x
C 6 H/ >-C/ >C,H ;
\ N / \ N /
C 6 H 6
This dyestuff and the bromo-derivative Ciba yellow G
(D.R.P. 246,837) were the first yellow vat dyestuffs for
wool ; they also dye cotton and silk from a vat. (Wuth,
J. Soc. Dyers and Col, 1911, 201; Engi, Chem.-Ztg. 9 1914,
199.)
294 ORGANIC DYESTUFFS
Although Indirubine itself is practically useless for
dyeing purposes, its bromo-derivatives possess a much
greater affinity for the fibre, and excel in purity of shade
and general fastness. Ciba heliotrope (E.P. 6106 (1907) )
is prepared by brominating Indirubine in presence of an
excess of nitrobenzene at 130 C. The Helindone dye-
stuffs of the Hochst Farbwerke are jalso substituted
derivatives of Indigoid compounds.
On condensation with isatin and subsequent bromina-
tion, methylindoxyl gives new violet dyestuffs, such as
Helindone violet D (M.L.B., E.P. 24,886 (1910) ).
Whereas the Anthraquinone derivatives are with very
few exceptions (for example, Helindone blue 3G) unsuit-
able for wool dyeing, the Helindone dyestuffs of the
Indigoid or Thioindigoid series are suitable for dyeing
on wool (Kammerer, J. Soc. Dyers and Col., 1913, 68),
for example, Helindone blue 2B 9 which is mainly 5 : 5'-
dibrom-Indigo :
co
c=c
It is interesting to note that Friedlander (Mon. sci.,
1909, 570) has recently proved the identity of Tyrian
purple with dibrom-Indigotine, which has the con-
stitution :
c=c
/
NH
This dyestuff of the Romans was extracted from a species
of mollusc found in the Mediterranean, known as the
murex brandaris.
INDIGO AND IND1GO1D DYESTUFFS 295
On condensing with acenaphthene quinone, oxythio-
naphthen gives an interesting dyestuff, for the pre-
paration of which the acenaphthene extracted from
coal-tar, which previously had no commercial application,
may be used. This product is known as Ciba scarlet G
(Soc. pour Vind. chim., Basle, D.R.P. 205,377), and has
the following constitution :
CO
co
The substitution derivatives of Thioiiidigo form a very
important class ; whereas the derivatives of Indigo do
not differ greatly in colour, those of Thioindigo cover
almost the whole range of the spectrum. Thioindigo
can be substituted in seven different positions :
The remarkable influence of substituents on the
colour is illustrated by the following examples (Fried-
lander, vol. ix, p. 502) : 6 : 6'-methoxy-thioindigo gives
an orange-red shade, the 4 : 4' compound, blue-violet ;
6 : G'-diamido-thioindigo gives an orange-brown shade,
the 4 : 4' compound, green-black ; 6 : G'-di-ethoxy-
thioindigo is a bright orange dyestuff, the 5 : 5' com-
pound, dark violet.
296
ORGANIC DYESTUFFS
The following Helindone [M.L.B.], Thioindigo [K.],
and Ciba [C.I.B.] dyestuffs are commercial, and are
derivatives of Thioindigo :
DYE STUFF.
PATENT No.
CONSTITUTION.
Thioindigo redBG.\
Helindone red B. j
D.R.P. 198,864
5 : 5'-Dichlorthioindigo.
Ciba red B.
E.P. 6490(1907)
6 : 6'-Dichlorthiomdigo.
Thioindigo red 3B.}
Helindone red 3#. /
Helindone Fast
D.R.P. 241,910
D.R.P. 213,465
5 : 5'-Dichlor-6 : 6'-di-
methylthioindigo.
5 : 5'-Dichlor : 6 : 6'-di-
scarlet R.
ethoxythioindigo.
Helindone grey BR.
D.R.P. 216,224
Dichlor- v 7 : 7 / -diamido
thioindigo.
Helindone violet 2B. \
Thioindigo violet 2B.J
D.R.P. 241,910
Dichlor-dimethyl-di-
methoxy- thioindigo.
Ciba bordeaux B.
E.P. 6490(1907)
5 : 5'-Dibrom-thioiiidigo,
Helindone pink BN.\
Thioindigo pink BN.j
D.R.P. 239,094
6 : 6'-Dibrom-dimethyl-
thioindigo.
Helindone orange D.
D.R.P. 198,644
Dibrom-6 : 6'-diamido-
thioindigo.
Helindone orange R. \
Thioindigo orange R. /
E.P. 1472(1907)
6 : 6'-Diethoxy-thio-
indigo.
Thioindigo scarlet S.\
Helindone scarlet S.f
D.R.P. 239,089
6 : e'-Dithioxyl-thio-
indigo.
Helindone grey 2B. ^
Thioindigo grey 2B.J
D.R.P. 241,910
7 : 7'-Diamido-thioindigo.
According to Bohn (Ber., 1910, 43, 987), the Indigoid
dyestuffs may be divided into symmetrical and asym-
metrical dyestuffs, and each of these groups may be
divided into three classes, as shown in the following
table. This classification does not include Oxindigo
C 6 H 4 <
CO^ ,CO
>c=c<
o/ x o
>C 6 H 4
which has recently been obtained by Fries and Hassel-
bach (Ber., 1911, 44, 124) and by Stormer and
Brachmann (Ibid., 315). This substance is unstable,
and 19 decomposed by caustic alkalies
INDIGO AND INDIGOID DYESTUFFS 297
Indigoid Dyestuffs.
I. SYMMETRICAL DYESTUFFS.
CLASS I.
CLASS II.
CLASS III.
Nitrogen
compounds.
Sulphur-nitrogen
compounds .
Sulphur
compounds.
Chromogen :
Chromogen :
Chromogen :
NH NH
S NH
S S
/ \ / \
C-C
/ \ / \
c=c
/ \ / \
c-c
\ / \ /
CO CO
\ / \ /
CO CO
\ / \ /
CO CO
Indigo and
derivatives.
Ciba violet and
derivatives.
TJiioindigo JSand
derivatives.
II. ASYMMETRICAL DYESTUFFS.
CLASS IV.
CLASS V.
CLASS VI.
Nitrogen
Sulphur-nitrogen
Sulphur com-
compounds.
compounds.
pounds.
Chromogen :
Chromogen :
Chromogen :
CO CO
CO CO
CO CO
/\ /\
/\ /\
/\ /\
C=C NH
C=C NH
c=c
\/ \/
\/ \/
\/ \/
NH
S
S
Indirubinc and
Thioindigo scarlet
Ciba scarlet G
derivatives.
and
and derivatives.
derivatives. '
CHAPTER XXII.
THIAZOL DYESTUFFS.
THE name thiazol has been given to a heterocyclic
ring containing three carbon atoms, one nitrogen atom,
and one sulphur atom. The first derivative of this
group known, phenylbenzthiazol, was obtained by
Hofmann by fusing benzanilide with sulphur :
^ NH
\
CO 6 H 6 + S
The simplest derivatives of thiazol are colourless.
Phenylbenzthiazol is, however, a chromogen, as the
introduction of basic groups in para-position to the
carbon of the thiazol ring gives feebly yellow coloured
substances.
The thiazol derivatives used in the manufacture of
dyestuffs are those obtained by fusing jp-toluidine or
its homologues with sulphur. This reaction was dis-
covered by Green in 1887 (Ber., 1889, 22, 969) and
led to the preparation of Primuline, the manufacture of
which was immediately undertaken by Brooke, Simp-
son and Spiller, near London. The process was not
patented, and the researches of Jacobson (Ibid., 331),.
Gattermann (Ibid., 424, 1064), Anschiitz and Schultz
(Ibid., 581). soon gave the chemical constitution and
method of preparation of this compound. Since that
time the manufacture of Primuline has been the subject
THIAZOL DYESTUFFS 299
of t a number of patents, mainly relating to the separation
of the products formed in the reaction, Primuline and
dehydrothiotoluidine .
Manufacture of Primuline.
When p-toluidine is fused with sulphur and the mass
heated to 200, sulphuretted hydrogen is liberated, and
there are produced two products, dehydrothiotoluidine
and Primuline, the relative amounts of w 7 hich depend
on the duration of the reaction, the temperature, and
the amount of sulphur. Dehydrothiotoluidine, or
jp-amidophenyltoluthiazol, results from the action of
four atoms of sulphur on two molecules of the base, thus :
4S
NH 2 + 3H 2 S
When the reaction lasts for a longer period, or is
carried out at a higher temperature, Primuline is pro-
duced by the action of sulphur on a molecule of de-
hydrothiotoluidine and a molecule of jo-toluidine :
-f 4S
300 ORGANIC DYESTUFFS
It is difficult to limit this reaction, and hence a
mixture of the two products is obtained. On heating
100 parts of p-toluidine with 60 parts of sulphur for
twenty-four hours, there is obtained a mixture containing
50 per cent, of dehydrothiotoluidine, 40 per cent, of
Primuline, and 10 per cent, of unchanged _p-toluidine.
The two bases may be separated by their different
solubilities in alcohol, Primuline being insoluble. In
order to obtain soluble dyestuffs it is necessary to
use the sulphonated derivatives of these bases, which
can be separated fairly easily commercially.
The reaction between sulphur and j?-toluidine is
carried out in a directly heated cast-iron vessel,,
closed by a cover carrying one or two fairly large
pipes surrounded by warm water, in order to condense
the vapours of the jp-toluidine without solidifying the
base ; the sulphuretted hydrogen which escapes is led
by a pipe to the fire where it burns. When the reaction
has commenced, the combustion of the sulphuretted
hydrogen formed supplies the heat necessary to maintain
the required temperature. When the liberation of gas
diminishes the reaction is finished, and the contents
of the vessel are forced into a sheet-iron tank and allowed
to solidify ; the yellowish brown mass obtained contains
a mixture of dehydrothiotoluidine and Primuline.
In order to sulphonate this product, it is first finely
powdered, and then added to four or five times its weight
of fuming sulphuric acid, containing 23 per cent, of
the anhydride, kept at 70. The sutphonation is
finished when the precipitate formed by pouring a drop
of the sulphuric acid solution into water is completely
soluble in caustic soda or sodium carbonate. The
sulphuric acid solution is then poured into water and
the precipitate separated ; it consists of a mixture of
the sulphonic acids of dehydrothio-j9-toluidine and
Primuline. For some preparations this mixture may
be used direct, but for others the products must be
separated. For this purpose the sulphonic acids are
THIAZOL DYESTUFFS 301
treated with concentrated ammonia solution, when the
ammonium salt of the sulphonic acid of Primulinc,
being very soluble, dissolves, whilst that of dehydrothio-
toluidine sulphonic acid is only slightly soluble and is
precipitated in the form of a paste of fine yellow needles
which is separated from the liquid. The solution ob-
tained is then treated with caustic soda, which replaces
the ammonia on heating, and by addition of salt there
is obtained the sodium salt of Primuline sulphonic acid,
which constitutes the Primuline of commerce.
Dehydrothio->-toluidine is insoluble in water, and
crystallises from alcohol in yellow needles of M.P. 191,
B.P. 434. Its sulphonic acid crystallises in small
yellow needles which are insoluble in water but soluble
in alkalies ; in dilute alkaline solutions it has a violet
fluorescence. The alkali salts have a very slight affinity
for cotton.
Primuline base is insoluble in water, and in alcohol.
Its sulphonic acid is an amorphous yellow powder which
is insoluble in water but soluble in alkalies, forming a
light yellow solution which has a violet fluorescence when
dilute.
Application of Primuline.
Primuline of commerce is the sodium salt of Primuline
sulphonic acid, and has the property of dyeing cotton
direct a greenish yellow shade, which of itself is not
of much interest. Primuline, however, contains a free
NH 2 group, which can be diazotised on the fibre and
then combined with amines or phenols to give various
shades. A. G. Green, who discovered this property,
gave the names " Ingrain " dyes tuffs to those which
are obtained directly on the fibre, thus indicating that
these dyestuffs are produced inside the cells of the
fibres. The production of Ingrain dyestuffs includes
three operations : dyeing, diazotising, and coupling or
developing.
302 ORGANIC DYESTUFFS
The dyeing of cotton with Primuline is carried out
under the same conditions as with the direct cotton
colours, that is, from a warm bath containing common
salt. The diazotisation is effected by immersing the
dyed fibre in a dilute solution of sodium nitrite acidified
with hydrochloric acid, and is complete in a few minutes.
After washing thoroughly, the dyestuff is developed by
immersing the fibre in an alkaline solution of a phenol,
a naphthol, or their derivatives, or in an acid solution
of an amine. The development is almost instantaneous.
The shades obtained are as follows : yellow with phenol,
orange with resorcinol, red with /3-iiaphthol, bordeaux
with ethyl-/3-naphthylamine, garnet with N.W. acid,
brown with m-phenylenediamine.
The Ingrain dyestuffs are very fast to washing, but not
to light. Green, Cross and Sevan (E.P. 7453 (1890) )
have applied the instability of the diazo-compound of
Primuline to light, in photography. The dyed material
is diazotised, washed and dried ; on placing under a
negative and exposing to the sun, the diazo-compound is
destroyed in the exposed places, and on developing
these portions remain yellow, whereas the remainder is
altered. This process, though interesting, has not
met with any commercial success.
Dyestuffs derived from Dehydrothiotoluidine.
Dehydrothiotoluidine has no affinity for cotton. On
methylating the free base by heating to 170 with
methyl alcohol and a mineral acid, a methyl chloride
compound of dimethyldehydrothiotoluidine is obtained,
which is soluble in water to a yellow solution :
CH 3
\C-C.H 4 -N(CH 3 ) 2
^ \
Cl
THIAZOL DYESTUFFS 303
This is a basic dyestuff, Thioflavine T (Green and
Lawson, J.C.8., 1889, 55, 230), which dyes wool and
tanned cotton greenish yellow shades.
When dehydrothiotoluidine sulphonic acid is oxidised
with an alkali hypochlorite, a yellow dyestuff is
obtained, which is known as Chlorophenine (Clayton
Aniline Co.) or Chloramine yellow, and which gives yellow
shades on cotton which are very fast to light. Oxida-
tion of the mixture of the sulphonic acids of dehydro-
thiotoluidine and Primuline gives a product, Oxyphenine,
the shade of which is not so pure.
Clayton ydlow or Thiazol yellow S. (D.R.P. 53,935) is
a direct yellow dyestuff, which is prepared by diazotising
dehydrothiotoluidine sulphonic acid and combining the
diazo- compound obtained with a further molecule of
that substance. It is not a true azo-dyestuff, as it no
longer contains the NH 2 group, but is very probably
a diazoamido- compound.
The higher homologues of ^p-toluidine, such as m-xyli-
dine and psemfo-cumidine, give similar compounds.
The Thiazol dyes tuffs are not destroyed by reducing
agents, and this property is used in printing for obtaining
coloured discharges.
CHAPTER XXIII.
SULPHUR DYESTUFFS.
THE Sulphur or Sulphide colours are prepared by
heating various organic substances with sulphur, alone
or^mixed with alkali sulphides. They are direct dye-
stuffs for vegetable fibres.
The first definite product was obtained by treating
crude dinitronaphthalene with alkali sulphides, but
the first commercial djrestuff of this class was discovered
by Croissant and Bretonniere in 1873 by heating saw-
dust, bran, and similar substances with sulphur and
alkali sulphides. This dyes tuff was known as Gachou
de Laval, and dyed cotton directly a greyish brown.
Its preparation from almost any organic debris, coupled
with its very weak tinctorial properties, did not en-
courage further research. The discovery remained at
this stage until 1893, when R. Vidal extended this
reaction in an unexpected manner. He found that
on heating a mixture of quinone and phenols with
sulphur and alkali sulphides in presence of ammonia,
intensely coloured dyestuffs were produced. On replac-
ing this mixture by p-phenylenediamine, p-amidophenol,
etc., he found that the latter substance, for example,
gave under these conditions a product which was soluble
in alkali sulphides, forming a green solution which dyed
cotton black ; this was called Vidal black, and was
manufactured by the firm of Poirrier at Saint-Denis.
The appearance of Vidal black was followed by that
of an enormous number of dyestuffs, obtained by
applying the above reaction to other organic substances.
The various colour firms have given the Sulphur dyestuffs
which they manufacture different names, as follows :
SULPHUR DYESTUFFS
305
Sulphur colours
Kryogen colours
Katigen colours
Immedial colours
Thioxin colours
Clayton colours
Pyrogen colours
Rexoll colours
Eclipse colours
Amidazol or
Sulpho colours
Cross dyes
Thiophor colours
Thion colours
Pyrol colours
Thionol colours
TJiiogen \
Melanogen J
Thional colours
Auronal colours
(Berlin Aktiejigesellschafi).
(B.A.S.F.).
(Bayer Co.).
(Cassella).
(Griesheim Elektron).
(Clayton Aniline Co.).
(Ba.sle Societe).
(Glaus & Co.).
(Geigy & Co., Basle).
(Read Holliday).
(Jager).
(Kalle Co.).
(Leonhardt).
(Levinstein) .
colours (Hochst Farbwerke).
(Sandoz).
(Weiler-Ter Meer).
The Sulphur dyestuffs have a certain number of
properties in common ; they are almost all coloured,
amorphous powders, insoluble in water, acids, and the
usual solvents. They dissolve in cold alkalies in the
presence of reducing agents, such as sodium sulphide or
glucose, and the solutions so obtained are decolorised by
stronger reducing agents such as hydrosulphites. On
immersion in these coloured solutions, vegetable fibres
absorb the dyestuff, which is partly fixed, and the
fixation is completed by passing through a warm, dilute
dichromate or copper sulphate bath, or in many cases
by mere exposure to air.
The Sulphur colours may also be precipitated from
solutions and fixed on the fibre by means of animal
colloids, such as glue, albumen, casein, etc. (Cassella,
D.K.P. 225, 314).
By evaporating a solution of a Sulphur dyestuff to
o, P. ' u
306 ORGANIC DYESTUFFS
dry ness with a caustic alkali and a reducing agent other
than sodium sulphide, such as glucose, a solid, stable
leuco-preparation of the dyestuff is obtained as an alkali
salt (Moistcr, Lucius and Bruning, E.P. 4510 (1912) ).
These products are useful on account of their solubility,
and can be used in the so-called lime-fermentation vat,
or the lime-glucose vat.
Manufacture of Sulphur Dyestuffs.
The methods used for manufacture have been further
improved since the discovery of Vidal black. These
improvements are to a large extent due to better know-
ledge, even yet incomplete however, of the chemical
reaction which gives these dycstuffs, Vidal was the
first to attempt an explanation ; he supposed that
on heating jj-cliamincs and jp-amidophenols with sulphur
and alkali sulphides, there is first produced a deriva-
tive of diphenylamine, which seems very probable, as
ammonia is liberated. The dyestuff is then formed
by the action of sulphur and alkali sulphides on the
substituted derivative of diphcnylamine so produced.
Vid al's view was subsequently confirmed, as a short
time afterwards the firm of f-assella obtained Immedial
black by fusing hydroxydinitrodiphenylamine with
sulphur and alkali sulphides. This discovery gave a
new impetus to the manufacture of Sulphur colours by a
different method to that previously employed. Various
derivatives of diphcnylamine, Mich as the hydroxy-,
amido-, alkylamido-, and chloro- compounds, and sul-
phonic and carboxylio acid derivatives, were fused with
sulphur and alkali sulphides. Hence, methods for
prc-paring these substances had to be found, as most of
them were then unknown, and they became raw materials
of very great importance.
Two methods are available by which these substances
can readily be prepared. The first is to treat substituted
aromatic amines with chlorclinitrobenzene. Whereas the
chlorine atom of monochl or benzene is only^ eliminated
with very great difficulty, the presence of the nitro-groups
SULPHUR DYESTUFFS 307
in chlordinitrobcnzene makes the chlorine easy to remove.
Thus, on healing in dilute alcoholic solution \vith
j)-amidophenol in presence of an alkali salt, chlordinitro-
benzene yields hydroxydinitrodiphenylamine, the raw
material used in. the manufacture of Immedial black,
thus: / v . /
)H
= NO 9 < > NH < >OH+HC1
The second method is to reduce Indophenols or Ind-
amines ; but this reduction need not actually be carried
out, as the sodium sulphide reduces the Indophenol or
Indamine, and the sulphur then converts the derivative
of diphenylamine so obtained into a dyestuff. An
attempt has also been made to replace the fusion method,
which is a rather destructive process, by the use of alkali
sulphides in the presence of a solvent such as alcohol,
glycerine, or even water. Finally, it has been found that
the presence of copper, manganese, zinc, etc., salts con-
siderably modifies the shade of the dyestuff formed in
these reactions.
Constitution of Sulphur Dyestuffs.
The constitution of most of the Sulphur dyestuffs
has not been definitely established ; indeed, the study
of these products is met with several difficulties. First
of all, they are generally amorphous substances which
are insoluble in the usual solvents, and are hence very
difficult to isolate in the state of purity essential for
examination. Moreover, in these reactions there are
often formed mixtures of several dyestuffs, which it is
difficult, if not impossible, to separate. Vidal supposed
that the sulphur contained in the products was combined
to form a certain number of thiazine rings. This view
has recently been confirmed by the discovery of a new
process for manufacturing Sulphur dyestuffs (A. O.
Green, Meyenberg, and the Clayton Aniline Co., DJLP.
308 ORGANIC DYESTUFFS
120,560, 127,856, 128,916, 130,440), which is in some
respects similar to that used for Methyl one bliie. On
oxidising with cold potassium dichromate in presence
of a large excess of sodium thiosulphate, a p-diamine or
a p-amidophcnol does not give Bcmthsen's mono-
thiosulphonic acid, but yields di- or tetra-thiosulphonic
acids, according to the experimental conditions. Thus,
jj-phenylenediamiue yields the two acids :
S SO 3 II HO 3 S S NH 2 S SO 3 H
no 3 s s NH 2 no 3 s s ]sn 2 s so
On oxidising with dichromate in presence of amines,
amidophonols, etc., these two acids yield, as inter-
mediate products, Indamine thiosulphoiiic acids, which
lose* sulphur dioxide on boiling with dilute mineral acids,
giving insoluble dyestuffs which have all the properties
of the Sulphur colours. This process makes it very
probable that thiazine rings are present in dyestuffs
of this group. All the sulphur is not, however, present
iu this form. It is known that on heating with sulphur
a large number of organic substances yield organic
disiilphides, which are generally only slightly soluble.
These disulphides are converted by reducing agents into
mcrcaptans, which are soluble in alkalies, and are easily
oxidised, regenerating the original insoluble sulphur
compounds.
The Clayton Aniline Co. (D.R.P. 140,964) have
obtained a process for preparing a blue dyestuff which
has made this view extremely probable. When a mixture
of dimcthyl-p-phenylenediamine thiosulphonic acid and
o-hydroxythiophenol is oxidised in alkaline solution, an
insoluble dyestuff very similar to, or identical with, the
Immcdial Pure blue of Cassella is obtained . The reaction
should therefore be represented by the following equation :
SULPHUR DYESTUFFS 30!)
NH 2
o
the mercaptan so formed then oxidising to give a di-
sulphide, which is the dycatuff :
(CH 3 ) 2 NC 6 H
S
O O
That vsuch a compound is soluble in alkaline reducing
agents (sulphides, or glucose and caustic soda) is explained
by the disulphide being converted on reduction into two
molecules of the mercaptan.
The thiazino constitution of Immcdial Pure blue has
also been confirmed by its conversion into tetrabrom-
Methylene violet (Gnehm and Kaufler, Ber. y 190 ! , 37,
2617, 3032),
Immedial Indone has been found by Frank (J.(7.^.,
1910, 97, 218) to give a dicarboxylic derivative
C L7 H lt 4 N 2 So, which requires two atoms of hydrogen
for its reduction to the leuco-compound. The con-
stitution suggested for this derivative is :
310 ORGANIC DYESTUFFS
There is another class of Sulphur dyestuffs known
which are obtained by fusing methyl ring-substituted
derivatives of ra-diamines with sulphur and alkali
sulphides. They are yellow, orange, or brown dyestuffs,
which appear to be somewhat similar to the Thiazol
derivatives, dehydrothiotoluidine and Primuline.
According to Nietzki (CJiemie der organischen Farb-
stoffe), the Sulphur dyestuffs may be divided provisionally
into the following six clasess :
(1) Immedial Yellow class. This includes dyestuffs
similar to those from thiazol, obtained from m-diamines,
particularly from w-toluylenediamine and its formyl,
acetyl, etc., derivatives. These compounds are fused
with sulphur, and the products so obtained are heated
with a concentrated solution of sodium sulphide, in
which they dissolve ; the dyestuff is then precipitated
by addition of an acid.
(2) Vidal Black class. Of the substances stated by
R. Vidal to give Sulphur colours on fusing with alkali
polysulphides, only p-amidophenol and dinitrophenol
give products of practical importance.
(3) Immedial Black class. These dyestuffs are ob-
tained by treating the derivatives of diphenylamine with
alkali polysulphides. The first of these products was
Immedial black, which rapidly replaced Vidal black.
(4) Immedial Pure Blue class. The Basle Soci6t6
pour 1'industrie chimique has prepared blue dyestuffs by
treating Indophenols, for example the one formed by the
oxidation of a mixture of dimethyl -p-phenylenediamine
and p-amidophenol, with alkali polysulphides. In the
same way, the firm of Cassella have obtained Immedial
pure blue dyestuffs by the action of polysulphides on
derivatives of diphenylamine at a low temperature.
(5) This class includes the violet and red dyestuffs
obtained by treating with sulphur the dyestuffs derived
from phenazine, such as amidooxyphenazine,Safra/ioles,
Rosindones, etc.
(6) This group contains the products obtained by
SULPHUR DYESTUFFS
311
treating 1 : 5- and 1 : 8-dinitronaphthalene, and the
intermediate products obtained in the manufacture of
naphthazarin, with alkali sulphides. The most im-
portant dyestuff of this group is Fast black (B.A.S.F.),
obtained by heating dinitronaphthalene with an aqueous
solution of sodium sulphide.
The following table gives the principal Sulphur dye-
stuffs (Nietzki, Chemie der organischen Farbstoffe, 5th
edition) :
DYESTTTFF.
PATENT No.
PREPARATION.
Vidal black [P.]
D.R.P. 82,748
Fusion of p-amidophenol
84,632, 85,330,
and p-diamines with
88,392, 91,719,
alkali polysulphides.
94,501
Fast black
D.R.P. 139,099
Dinitronaphthalene is
[B.A.S.F.]
treated with alkali
sulphides in aqueous
solution.
Immedial black V.
D.R.P. 103,861
Fusion of hydro xydinitro-
[C.]
diphenylamine with
alkali polysulphides.
Sulphur black T.
D.R.P, 127,835
Dinitrophtfnol is treated
[A.]
with an aqueous solu-
tion of polysulphides.
Auronal black
D.R.P. 144,119
p-Amidodinitrodiphenyl-
[W.]
amine is treated with
sulphides in presence
of glycerol.
Katigen black 2B.
E.P. 15,625.
From chlordinitrophenol.
[By.]
Immedial blue
D.R.P. 103,861,
Hydroxydinitrodiphenyl-
[C.]
104,283
amine is treated with
polysulphides at a low
temperature.
Pyrogen direct
blue,
D.R.P. 132,424
Hydro xydinitrodiphenyl-
amine is treated with
Pyrogen blue R.
polysulphides in alco-
[C.I.B.]
holic solution.
Immediai Pure
D.R.P. 134,947
p-Dimethylamidohydroxy-
blue [C.]
diphenylamine is
treated with sulphur.
Pyrogen yellow M.
D.R.P. 135,335
Fusion of oxybenzylidene
Pyrogen olive
[C.I.B.]
compounds with poly-
sulphides.
312
ORGANIC DYESTUFFS
DYESTUFF.
PATENT No.
PREPARATION.
Eclipse yellow O
and 3G [G.].
Immedial yellow D
[C.]
Immedial orange O
[C.]
Verde Italiano.
Pyrogen green
Immedial bor-
deaux [C.]
Immedial maroon
[C.]
D.R.P. 138,839
D.R.P. 139,430
D.R.P. 152,595
Lopetit, Dollfuss
&Co. (1896).
D.R.P. 148,024
D.R.P. 126,175
Fusion of mono- or di-
formyl-7W-toluylene
diamine, alono or
mixed with benzidine,
with sulphur at 240 C.
Fusion of ra-toluylene di-
amine with sulphur at
190C.
Fusion of m-toluylene di-
amine with sulphur at
250 C.
Fusion of p-amidophe-
nol or its substituted
derivatives with poly-
sulphides in presence of
copper salts at 180 C.*
Fusion of azines with
sulphur and alkali
sulphides.
The proportions of sulphur and sodium sulphide, and
of the polysulphide to the raw material used, the tempera-
ture at which the reaction is carried out, and the methods
used for the separation of the dyestuffs, all play an
important part in determining the product which will
be obtained. In many cases the best conditions lie
between very small limits. The field being so extensive,
in fact almost every class of organic compound appears
to have been submitted to the action of sodium poly-
sulphide, it is not surprising to find that products have
been obtained which have subsequently been found to
be mixtures of dyestuffs and their intermediate products.
Taking into account the complexity of these dyestuffs,
the chemical constitution of which is generally unknown,
it is remarkable that there should not have been more
cases of the patents of different firms clashing. Many
of VidaPs patents were incomplete ; thus E.P. 16,449
(1896) is an example of how to produce a Sulphur black
from dinitrophenol under the worst possible conditions.
SULPHUR DYESTUFFS
313
The compounds, and in some cases the methods, used
for obtaining some of the recent yellow and brown
dyestuffs are given in the following table. (See Vlies,
J. Soc. Dyers and Col., 1913, 316.)
Kryogen yellow R.
Thion yellow 0.
Immedial yellow GO.
Kryogen yellow G.
Thion brown.
Eclipse brown colours.
Thio Katigen colours.
Immedial brown.
Immedial bronze.
Thiophor bronze 5G.
99 99
Kryogen brown.
G.
Thional brown G, etc.
Thional bronze.
m-Toluylonediamino thiourea.
m-Toluy lenediamiiie .
Dohydrothiotoluidine mixed with benzi-
dine.
Thiourea derivatives of w-toluylene-
diamine mixed with benzidine.
Aniline-azo-ra-toluyleiicdiamine.
Mixtures of m-toluylencdiamino with
several bases and acids, such as
oxal-m-toluylenediamine, nitrotolui-
dines, phthalic acid, thio-diglycollic
acid, etc.
Fusion of acetyl-p-phonylenediamine
with sulphur and solution in sodium
sulphide ;
or Action of sodium polysulphide on
nitro-acetanilide, etc.
Action of caustic soda on hydroxydinitro-
diphenylamiiie, which may be fol-
lowed by fusion of the product with
sodium polysulphide.
Fusion of dinitrocresol with polysul-
phide.
Fusion of a mixture of p-phenylenedi-
amino and p-amidoacetanilide with
sulphur.
As above, but with addition of bonzi-
dine.
Reduction of 1 : 8-dinitronaphthaleno
with sulphide or sulphite and sub-
sequent treatment with polysulphide.
Fusion of /3-oxynaphthaquinone anilides
with sodium polysulphide.
The enormous number of Sulphur dyestuffs produced
during the ten years which followed Vidal's discovery
has left behind a host of prematurely extinct patents,
and has been followed by a period of inactivity which is
remarkable. During the last two years the production
of new Sulphur dyestuffs has been so small that one
314 ORGANIC DYESTUFFS
might reasonably conclude that this group of colouring
matters is not capable of any great extension. The
original Vidal black from p-amidophenol appears to be
no longer manufactured. Cheaper colours of higher
tinctorial powers, such as the Rexoll blacks (Glaus and
Co.), have taken its place.
The Sulphurised Vat Dyestuffs.
The new " Hydron " dyestuffs of Cassella and similar
products must not be confused with the Sulphur colours.
Although produced by the action of polysulphides on
certain organic compounds, they are vat dyestuffs, and
are insoluble in sodium sulphide. The chemical con-
stitution of these dyestuffs is quite unknown ; they may
be divided into :
(1) Sulphurised anthracene derivatives.
(2) Sulphurised vat dyestuffs of Indophenols and
allied compounds.
Sulphurised anthracene derivatives.
These compounds are prepared by melting anthracene
and several of its more or less complicated derivatives
with sulphur at high temperatures. The simplest
representative is Indanlhrene olive (D.R.P. 186,990),
which is obtained by melting anthracene with sulphur
at 250 C., and giveS olive shades fast to light and washing
from a dark violet coloured vat. Hydron olive G [C.]
is probably a similar dyestuff prepared by the action of
sulphur chloride on anthracene (D.R.P. 247,416) at a
high temperature.
Cibanone blue 30 and black B (E.P. 20,094 (1908) ), and
probably the later brands, Cibanone green B and black 2B 9
are produced by treatment of 2-methylbenzanthrone
with sulphur. 2-Methylanthraquinone, and also this com-
pound halogenated in the methyl group, on fusion with
sulphur, gives rise to compounds which possess dull and
worthless shades, but on oxidising with hypochlorites
SULPHUR DYESTUETS 315
are transformed into bright orange dyestuffs. Cibanone
yellow R (E.P. 7583 (1908) ) from to-monochlor-methyl-
anthraquinone, and Cibanone orange R, from the dichloro-
derivatives, are so obtained.
Amido- and diamido-2-methylanthraquinone melted
with sulphur give yellow to violet brown dyes. Cibanone
brown (E.P. 13,057 (1908) ) is probably prepared from
the mono-amido compound.
Sulphurised Vat Dyestuffs from Indophenol.
The colouring matters obtained by heating many
organic compounds with sodium polysulphide, chiefly
the tetrasulphide, are known as Sulphur dyestuffs. If,
however, a poly-sulphide approaching the hypothetical
Na 2 S 7 and Na. 2 S 8 acts upon certain Indophenols, new
dyestuffs are obtained which no longer dissolve in sodium
sulphide, but form soluble leuco-compounds with
hydrosulphite, and behave like true vat dyes.
L. Haas (E.P. 2918 (1909) ) found that carbazol
condenses with nitrosophenol in sulphuric acid solution,
producing an Indophenol, analogous to the Indophenol
of diphenylamine prepared in the same way, thus :
/NH-
Indophenol of diphenylamine.
X NH\
Indophenol of carbazol.
On heating with the usual proportion of sodium
sulphide and sulphur, Indophenol-carbazol gives a blue
Sulphur colour. The addition' of copper sulphate to
316 ORGANIC DYESTUFFS
the mixture gives a product which dyes black shades,
and is commercial as Indocarbon S [C.].
More intensive sulphurisation of Indophenol-carbazol
or of its substitution products, alkyl or acyl derivatives,
or of the condensation product of dinitrochlorbenzene
with leuco-Indophenol-earbazol leads to the production
of entirely different dyestuffs, which appear in commerce
as Hydron blue R, G, B (D.R.P. 224,590-1 ; E.P. 956,348,
Hertz and Cassclla) and Hydron blue-black.
The trade name " Hydron " of Cassella does not only
include carbazol dyestuffs, but also embraces vat dye-
stuffs belonging to other groups ; for example, Hydron
yellow G is not a Sulphur vat dyestufi, and may be one
of the colours obtained by condensing a diphthaloyl
carbazol by means of sulphuric acid or other dehydrating
agent (E.P. 28,874 (1911) ). Grandmougin states that
Hydron violet B resembles the Indigoid dyestuffs. All
Hydron colours can be dyed in combination with one
another. Hydron blue G and R approach Indigo in
shade, being somewhat greener and redder respectively :
Erban (Farb.-Ztg., 1911) states that they are faster to
washing, boiling, and bleaching than Indigo.
CHAPTER XXIV.
ANILINE BLACK.
Aniline black is an insoluble dyestuff which is pro-
duced on treating aniline with acid oxidising agents.
Its formation was noticed by Runge as early as 1834.
Aniline black is not used in the solid form for printing
cotton, but is always prepared directly on the fibre by
special dyeing or printing processes.
The first application of Aniline black in dyeing was
made in England by Gal vert, Clift and Lowe in 1862.
The fibre was immersed in a solution containing aniline
hydrochloride, potassium chlorate and an iron salt ;
it acquired a green shade, which \\as converted into
black by subsequent passing thiough warm dilute
bichromate (" chroming "). In the following year,
Lightfoot improved the method, having observed that
the presence of traces of a copper salt accelerated the
formation of the black, the copper salt acting as an
oxygen carrier. The black so obtained developed at
a relatively low temperature (40-50) in moist air.
Lightfoot 's method is still used at the present time,
but has undergone certain modifications. Thus the
presence of soluble copper salts has the disadvantage
that they attack the steel doctors of the machines
used in calico printing. In 1864 this difficulty was
overcome by Lauth J(Mon. sci., 1865, 58) by adding to
the mixture an insoluble copper salt, such as the sulphide,
which is, however, oxidised on exposure to moist air
and then becomes soluble. In 1876, Guyard and Witz
318 ORGANIC DYESTUFFS
discovered that vanadium salts exert a much more
energetic catalytic action than copper salts ; thus one
part of vanadium is sufficient to promote the oxidation
of 270,000 parts of aniline salt mixed with potassium
chlorate. In order to prevent the tendering of the
cotton fibre, which always takes place on dyeing with
Aniline black, the copper or vanadium salts are replaced
by ferrocyanides, which also neutralise the acidity due
to the hydrochloric acid liberated from the aniline
hydrochloride.
Ferrocyanide blacks are often called Steam blacks.
The three methods available for the production of
Aniline black may be summarised as follows :
1. Single Bath black. This method is used chiefly for
yarn dyeing. The fibre is sometimes bottomed with a
Sulphur black, on which the Aniline black is then pro-
duced by immersing the cotton in a solution containing
aniline salt, potassium dichromate and hydrochloric acid,
in which it is worked in the cold, or better, slowly brought
to the boil. The dyestuff is produced in the bath, a por-
tion remaining on the fibre. If the black has been obtained
in the cold the process must be finished by steaming.
2. Aged black. This is very much used for dyeing
of pieces, but may also be used with certain precautions
for hank dyeing. The method consists in padding the
fibre with a solution containing aniline salt (which has
been made basic by the addition of a small quantity of
aniline), sodium chlorate, and copper sulphate. After
the fibre has been wrung out, it is passed into an
oxidation chamber in which the air is heated to
40-50 C., and kept sufficiently moist by means of steam.
After leaving this chamber the fibre has a dark green
colour due to the presence of emeraldine ; the oxidation
is finished by passing through warm dichromate solution,
which converts the emeraldine into Aniline black. (See
also N. Evans, J. Sac. Dyers and Col., 1910, 26, 117.)
A. G. Green has found that oxidation with chlorate
may be replaced by oxidation with air alone, by adding
ANILINE BLACK 319
to the mixture of aniline salt and the copper s,alt a trace
of 2>-phenylenediamine or p-amidophenol (E.P. 16,189
(1907) ), these substances acting as catalysts. Deriva-
tives of p-phenylenediamine, and certain nitroso-com-
pounds may also be used (Zeidler and Wengraf, D.E.P.
223,404, 224,384). This process has a great future, as it
does not damage the fibre.
3. Steam blacks. These are used for dyeing pieces,
and mainly for producing resists in printing. After
padding in a bath containing aniline salt, sodium chlorate,
and potassium ferrocyanide,the material is wrung out and
steamed for two or three minutes in a rapid ager. The
formation of the black is almost complete, the oxidation
being finished by passing through bichromate. If the
material has been printed with an alkaline substance
before steaming, the black does not develop in the printed
parts, and white resists are obtained (Prudhomme).
At the present time, Aniline black is one of the most
important of all colouring matters in cotton dyeing and
calico printing.
Constitution of Aniline Black.
Three stages may be distinguished in the oxidation
of aniline : a green substance (emeraldine) is first pro-
duced, which is converted into a black, and this eventu-
ally becomes green (nigraiiiline), and by more complete
oxidation becomes an ungreenable black. In spite of a
considerable number of researches, the constitution and
even the composition of the black remained undeter-
mined for a considerable period, although some light-
was thrown on the subject by the researches of Caro,
and more recently by those of Willstatter (Willstatter
and Moore, Ber., 1907, 40, 2665 ; Willstatter and
Dorogi, ibid., 1909, 42, 2148, 4118; Willstatter and
Cramer, ibid., 1910, 43, 2976; 1911, 44, 2162. See
also Nover, Ber., 1907, 40, 288, and A. G. Green,
J. Soc. Dyers and Col, 1909, 189). According to
Kayser, the composition of the black corresponded
320 ORGANIC DYESTUFFS
to C 12 H 10 N 2 ; according to Nietzki it was C 18 H l& N3,
according to Goppelsroder, C24H 20 N 4 ; later analyses of
Nietzki lead to the formula CaoH^N^ and finally
Willstatter and Moore gave the minimum formula
asC 48 H 36 N 8 .
Caro has shown that on oxidation of aniline by
potassium permanganate in cold aqueous solution, a
yellow solution is obtained, from which an amorphous
yellow substance may be extracted with ether which
gives emeraldine on treatment with acids. This yellow
substance has been isolated in a crystalline state by
Willstatter and Moore, who have established its con-
stitution as that of phenylquinonediimide :
C 6 H 5 N = C 6 H 4 = NH.
In contact with acids it is converted entirely into
emeraldine, the base of which has been obtained in a
crystalline condition, its molecular weight correspond-
ing to C 24 H 20 N 4 . It is hence a polymer of the above
yellow substance. Oxidation of this base in benzene
solution yields a red compound, C 24 H 18 N 4 , which on
polymerisation finally gives ungreenable Aniline black.
As emeraldine was formed by the condensation
of phenylquinonediimide, the following formula was
incorrectly assigned to it by Willstatter and Moore, the
bonds being in yarn-position :
C 6 H 5 N = C 6 H 4 N C 6 H 4 NH C 6 H 4 NH 2
The red base obtained by oxidation contains two
atoms less of hydrogen ; its constitution may be repre-
sented by :
C 6 H 5 N = C 6 H 4 =N C 6 H 4 N =C 6 H 4 =NH
This base polymerises even on heating with water
in a sealed tube, giving an amorphous powder which
is the Aniline black called " polymerisation black."
The formula should therefore be (C 24 H 18 N 4 ) a} , and for
the minimum value x = 2, the formula becomes C 48 H 36 Ng,
which is the simplest possible formula for Aniline black.
ANILINE BLACK 321
The constitution of Aniline black has now been
elucidated by A. G. Green and S. Wolff (Ber., 1913, 46, 33 ;
J. Soc. Dyers and Col., 1913, 105). It has been shown
that the products obtained by earlier investigators, in-
cluding those of Willstatter, consist of impure emeraldine
or nigraniline (Green and Woodhead, J.C.S., 1910. 97,
2388 ; and Green and Wolff, Ber., 1911, 44, 2570 ;
J.C.S., 1912, 101, 1117). Green states that these pro-
ducts are merely mixtures of emeraldine and nigraniline
with a variable amaunt of polymerisation or decom-
position compounds, produced by the action of the
mineral acid employed for " purification," as none of
these substances exhibit the characteristic behaviour
of an ungreenable Aniline black formed on the fibre,
which alone can be regarded as a true Aniline black.
The oxidation of aniline to Aniline black has been shown
by Green and Wolff to proceed by a series of quinonoid
additions according to the scheme shown on next
page.
In a later paper, Green and Johnson (J. Soc. Dyers
and Col., 1913, 338) give the results of investigations
which further confirm the above formula for the hydro-
chloride.
On oxidation with lead dioxide suspended in dilute
sulphuric acid, and allowing 5 per cent, for loss by over-
oxidation, the yield of quinone obtained from the
Aniline black of Green and Wolff was 52*5 per cent.,
corresponding very closely to that theoretically indicated
by the phenylazonium formula.
The above authors have also investigated the variety
of Aniline black known as " Single Bath black " or
" Bichromate black." The samples obtained by various
practical methods had in general the same properties,
differing only in the amount of impurities present. It
is to be noted that the name " Aniline black " cannot
properly be applied to any of the products prepared by
Willstatter and his pupils, as Green and Wolff have
shown them to be mixtures of emeraldine and nigrani-
a
55
aV
** "C
&~
o
O f
+ 1
s r i
^
=J K
J 55
o
o
o o y
I
1
I
K
55
W
o
a
55
a
55
55
o
o
525
cJ
O
a
o*
S3,
d 9
52!
d 9
"4
O
o
52;
d 9
CD S
6 H 5 NH 2
ANILINE BLACK
323
line. The results show that Bichromate black is an
analogue of the Chlorate black, being a phenylazonium
hydroxide :
W-
H
0)
a
O
a
1
1
W
I X
I
i
324 ORGANIC DYESTUFFS
as the presence of an OH group explains the difficulty
experienced in removing the chromium, and the smaller
solubility of the base in acetic acid. Further Bichromate
black differs from the other quinonoid bases of the
series in having a maximum combining capacity of two
molecules of hydrochloric acid in place of three ; as
usual in this series, the dihydrochloride is not hydrolysed
by water.
BOOKS OF REFERENCE.
H. BUCHERER. Die Teerfarbstoffe. Goschen, Leipzig.
1904.
H. BUCHERER. Lehrbuch der Farbenchemie. Spamer.
Leipzig. 1914.
J. 0. CAIN AND J. F. THORPE. The Synthetic Dyestuffs.
Griffin, London. 1913.
H. CARO. Ueber die Entwicklung der Teerfarbenindustrie.
Friedlander, Berlin. 1893.
W. A. DAVIS AND S. S. SADTLER. Allen's Commercial
Organic Analysis. J. A. Churchill, London.
1912.
FABRE AND GUYOT. La chimie des matidres colorantes
organiques. Carre, Naud et Cie, Paris. 1901.
F. J. FARRELL. Dyeing and Cleaning. Griffin, London.
1912.
F. FELSEN. Der Indigo und seine Konkurrenten. Berlin.
1909.
F. FELSEN. Turkischrot und seine Konkurrenten. Berlin.
1911.
J. FORMANEK AND E. GRANDMOUGiN. Untersuchung und
Nachweis organischer Farbstoffe auf Spektro-
skopischen Wege. Springer, Berlin. 1911.
P. FRIEDLANDER. Die Fortschritte der Teerfarben-
fabrikation und verwandter Industriezweige. Julius
Springer, Berlin. 1877-1913. 10 vols.
326 BOOKS OF REFERENCE
GEOKGIEVICS AND GRANDMOUGIN. Lehrbuch der chemi
schen Technologic der Gespinstfasern. Teil I.
Lehrbuch der Farbenchemie. Deuticke, Vienna.
1913.
A. G. GREEN. The Identification of Dyestuffs on Vege-
table Fibres. Goodall and Suddick, Leeds, 1910.
A. G. GREEN. The Identification of Dyestuffs on Animal
Fibres. Goodall and Suddick, Leeds. 1913.
A. HALLER. Rapport sur VExposition Universelle 1900,
Class 87. Impr. nationale, Paris. 1901.
W. HARMSEN. Die Fabrikation der Teerfarbstoffe.
Fischer, Berlin. 1889.
HEUMANN. Die Anilin Farben. Vieweg, Braunschweig.
J HUBNER. Bleaching and Dyeing of Fibrous Vegetable
Materials. Constable, London. 1912,
G. F. JAUBERT. Historique de I'industrie suisse des
matieres color antes artificielle. George et Cie,
Geneva. 1896.
E. KNECHT, C. RAWSON, and R. LOEWENTHAL. A
Manual of Dyeing. Griffin, London. 1910.
E. KNECHT AND E. HIBBERT. New Reduction Methods
in Volumetric Analysis. Longmans, Green
& Co., London. 1910.
0. LANGE. Die Schwefelfarbstoffe. Spamer, Leipzig.
1912.
L. LEF&VRE. Les matieres coloranles. Masson, Paris.
1897. 2 vols.
LEHNE. Tabellarische Uebersicht der kunstlichen or-
ganischen Farbstoffe. Springer, Berlin. 1893.
G. LUNGE. Coal Tar and Ammonia. Gurney and
Jackson, London. 1909.
G. LUNGE AND C. A. KEANE. Technical Methods of
Chemical Analysis. Gurney and Jackson, Lon-
don. 1911. 2 vols.
BOOKS OF REFERENCE 327
MOHLAU. Organische Farbstoffe. J. Blom, Dresden.
1890.
MOHLAU AND BUCHERER. Farbenchemisckes Praktikum.
Leipzig. 1908.
S. P MULLIKEN. Identification of Commercial Dyesiuffs.
Chapman and Hall, London. 1910.
R. NIETZKI. Chemie der organischen Farbstoffe. 5th
edition. Springer, Berlin. 1906.
NOLTING, LEHNE AND PICQUET. Le Noir d' Aniline.
" Revue generate des matieres colorantes," Paris.
1908.
L. PELET-JOLTVET. Die Theorie des Farbeprozesses.
Steinkopf , Dresden. 1910.
REVERDIN AND NOLTING. Sur la constitution des derives
de la naphtaline. Bader, Mulhouse. 1888.
F. REVERDIN. Analyse des matieres colorantes or-
ganiques. Eighth Congress of Applied Chemistry,
New York. 1912.
SEYEWITZ AND SISLEY. La chimie des matieres colorantes.
Masson, Paris. 1896.
G. SCHULTZ. Die Chemie des Steinkohlenteers. Vieweg,
Braunschweig. 1900. 2 vols.
G. SCHULTZ. Farbstofftabellen. Wiedinann, Berlin.
1911-3.
TAUBER AND NORMANN. Die Derivate des Naphtalins.
Gartner, Berlin. 1896.
E. THORPE. Dictionary of Applied Chemistry. Long-
mans, Green & Co., London. 1912.
L. E, VLIES. Recent Progress in the Colouring Matters
and their Application. Journ. Soc. Dyers and
Col., 1913, 316 ; 1914, 22, 99.
WAGNER, FISCHER AND GAUTHIER. Chimie industrielle.
Masson, Paris. 1903.
A. WAHL. Progres realises dans Vindustrie des matieres
colorantes. Mon. sci., 1902, 1903, 1904, 1907.
328 BOOKS OF REFERENCE
J. WALTER. Aus der Praxis der Anilinfabrikation.
Jaenecke, Hanover. 1903.
J. K. WOOD. The Chemistry of Dyeing. Gurney and
Jackson, London. 1913.
A. WURTZ. Dictionnaire de chimie pitre et appliquee.
Hachette, Paris. 14 vols.
Note. For details of the character and contents of
recently published books, readers should refer to the
reviews in the Journal of the Society of Dyers and
Colourists, which also contains abstracts of many of the
important papers to which reference has been made.
INDEX.
PAC, K
Abbreviations xi
Aeotanilido 66
7-Acid - 65
5-Acid - ... 42
Acid dye-stuffs - - 81
Alizarin black R - - 114
Alizarin blue - 215
blue 6G - - - 151
green S - - - 150
Magenta - - -105
violet 6B, 10B - - 169
yellow 88
yellow G - - - 104
Acridine dyestuffs - - 195
orange - - 198
red B - - - - 185
yellow - - - 198
Acridinium compounds - 199
Acylated compounds - 66
Adjective dyestuffs - 80
Afghan yellow - 135
After-chromed dyestuff - 96
Aged black - - 318, 322
Algol blue CF, 3G - - 222
blue K - - - 223
blue 3H - - - 230
bordeaux 3B - - 229
Brilliant orange FR - 230
Brilliant red 213 - - 230
Brilliant violet 2B, R - 230
green B 223
grey B 229
olive R 230
orange R - - - 229
pink R 230
rodB- - - 220,231
red 5G, R extra - - 230
PAOE
Algol scarlet G - - 230
violet B 230
yellow WC, 3G, R - 230
Alizadine colours - - 114
Alizarin - - - 203, 222
constitution of - - 203
distinction of natural - 213
manufacture of - - 206
properties of - 210
synthesis of 205
S - - - - 211
GI, RG, SDG, X - 213
Acid blue BB, GR - 215
Astral - - - 217
blue - 219
blue S - 219
blue-green - 220
bordeaux - - 214
Celestol - - - 218
Cyniiine - - 215
Cyaiiino given - - 217
green S [M.L.B.] - - 219
green S | B.A.S.F.] - 220
indigo blue - - - 220
Irisol - - - - 218
orange - - - 211
Saphirol - - - 217
Viridine DG, FF - 214
yellow R, GG - - 113
Alkali blue - -171, 173
blue XG - 172
Alkaline fusion - - 33
practical details of - 34
Alkylation 68
Alsace green 92
Amethyst violet - - 263
Amidazol colours - - 305
330
INDEX
PAGE
Amido G acid 63
R acid 63
Amidonaphthol sulphonic
acids - - 65
Amidophenols - - 64
alkylated - - 72
Amines, primary - 53, 70
secondary 70
tertiary 70
Aniline - - - 55
manufacture of - 56
" Aniline oil for blue " 57, 170
" Aniline oil for red " 157, 170
" Aniline salt " - - 58
Aniline black- 317, 321, 322
constitution of - 319
ungreenablo - 319, 321
Aniline blue - 170, 171, 172
red - - - - 1
violets - - - 166
yellow - - - 104
Anisolo 69
Anisolino - - - 194
Anisolines - - 193
Anthracene - - 10, 17
dyestuffs - - - 200
vat dyestuffs - - 220
blue - - - - 215
brown - - 212
Chrome black - - 114
Anthracyanines - - 253
Anthraflavic acid - - 202
Anthraflavono - - 224
Anthragallol - - - 212
Anthranilic acid - - 284
Anthrapurpurin - - 213
Anthraquinone - - 200
dyestuffs - - - 200
manufacture of - - 207
sulphonation of - - 207
vat dyestuffs - 220, 231
Anthraquinone violet - 217
Anthraquinoneimides - 229
Anthrarufin - - - 212
Aposafranine - - - 261
Aposafranines - - 257
Arnica yellow - - 135
Auramine - - - 139
Auramine G - - - 140
Aurantia - - 89 i
Auriiio -
PAC1K
- 176
Auronal colours
- 305
black -
- 311
Auxochromos -
81
Azaloin -
- 153
Azidino Fast scarlets
- 119
Aziries -
- 254
Azobenzone -
- 100
Azococcme
- 108
Azococcirie 21!
- 108
Azocorinth
- 128
Azo-dyestxiffs
94
chrome-developed
96, 113
classification of -
- 100
disazo
- 115
monoazo
- 100
mordant monoazo
- 113
tetrakisazo
- 127
trisazo
126, 128
Azoeosine'
- 108
Azof la vine S -
- 105
Azomageiitas
- Ill
Azophcnino -
- 265
Azophenosafraninos
- 262
Azorubine S -
- 108
Azorubirie 2B
- 109
Azo yellow
- 105
Azoxy-compounds - 54
Azthionium derivatives 182,241
Azulino -
- 177
Basic dyestuffs
- 81
Basle blue
- 263
Bavarian blue
- 172
Bayer acid
41
Benzanthrone
- 227
Benzauririo
- 175
Benzene
10, 13
Beiizidino
- 122
Benzo blue-black R
- 128
Brilliant blue
- 172
Fast scarlets
- 118
olive -
- 128
orange R -
- 125
scarlets
- 124
Benzoflavirio -
- 198
Benzols -
9, 15, 16
Benzophenono
- 137
Benzopurpurino 4B,
10B 125
Benzyl violet
- 169
INDEX
331
Bichromate black -
Biebrich black, Patent
Biebrich scarlet
Bindschedler's green
preparation of -
Bismarck brown
Blue-black B -
Bordeaux B -
Brilliant Crocein
green -
orange
Ponceau
Bronner's acid
Cachou do Laydl -
Capri bhje>/ x -
CarbinoTs
Carbolic acid -
Celestine blue
Cerise -
Chicago orange
Chloramine yellow -
Chlorate black
Chlorophenino
Chromacetine blue -
Chromanthrene colours -
Chromazurine G, E
Chromazurol S
Chrome-developed
dyes tuffs
Chroming
Chromogens -
Chromophorcs
Chromotropes
Chromotropic acid
Chromoxan colours
Chrysanilino -
Chrysazin
Chrysoidine -
Ciba dyestuffs
blue B, 2B -
bordeaux B
heliotrope -
red B -
scarlet G -
violet -
yellow G
Cibanone black B, 2B
blue 3G
brown
PAGE
321, 323 Cibanone green B -
PAGE
- 314
- 120
orange R -
- 315
119, 120
yellow R
- 315
- 235
Citronino
- 105
- 236
Citronine A -
88
106, 121
Clayton colours
- 305
- 120
yellow
- 303
- 109
Cleve's acids -
62
- 120
Cloth red B, G
- 120
- 149
scarlet G
- 120
- 109
Coal Tar
7
- 109
composition of -
8
63
treatment of
- 8, 11
Ccerule'ine
- 191
- 304
Cceruleme S -
- 191
- 247
Colour and structure
75
142, 145
nature ot -
- 75
- 9, 18
Congo Corinth G
- 125
- 253
red -
122, 125
- 159
Corallin, red -
- 177
- 135
yellow
- 177
- 303
Cotton blue -
- 172
- 322
Cotton blue R
- 249
- 303
Coupling
- 96
- 253
of diazo-compounds
99
s - 114
of tetrazo -compounds - 124
- 254
rules for
102, 106
- 176
Crosols -
19
Crocein acid -
40, 41
96, 113
3BX -
- 109
- 317
orange
- 109
76
Cross dyes
- 305
76, 82
Crystal scarlet
109, 110
- Ill
violet
166, 169
66
^-Cumeno
15
- 176
Curcumin
- 135
159, 198
Curcumin S -
- 135
202,212
Curcuphenin -
- 135
- 105
Cyanaminos -
- 250
- 293
Cyanol -
'- 151
- 293
Cyanosine
- 190
- 296
Cyanthrene -
- 227
- 294
- 296
Dahl's acids -
62
- 295
Dehydroindigo
- 270
- 297
Dehydrothiotoluidine
299, 302
- 293
Delphine blue B
- 254
- 314
Diamines
- * 53
- 314
Oiomine black BH, 3O
,RO 125
- 315
blue 2B, 3B, BX
- 125
332
INDEX
Diaminc bronzo G -
brown
brown V -
green B - - 120,
scarlet
Sky blue -
violet N
Diaminogens -
Diaminogen black -
blue G
Diamond black P.V.
Flavine
Magenta
yellows
Dianil blue G
Dianisidine
Dianthine
Diazo Brilliant scarlet -
Diazo-compounds -
coupling of
Diazonium salts
Diazotisation
apparatus for
Dimethylaniline
Dimethyl-p-phenyleno-
diamine
Dinitrobenzene
Dinitronaphthalenes
Dinitrosoresorcinol
Dinitrotolueno
Dioxin -
Dioxindol
Diphenazino -
Diphenetidine
Diphenoxazine
Diphenylamine
blue - - - 171,
orange ...
Diphenylmethano
dyestuffs
Direct dyestuffs 80, 113,
yellow G -
yellow RT -
yellow, preparation of
Disazo-dyestuffs - 114,
DObner's violet
Dyeing, mechanism of -
process of -
" Dyer's woad "
Dyestuffs, acid
126
Dyostuffs, additions to
-
100
125
adjective
-
80
125
analysis of -
-
102
128
application of
-
74
125
basic -
,
81
125
classification of -
-
74
125
definition of
_
78
127
direct - - 80,
112,
121
120
mordant - 79,
113,
200
127
nature of -
-
80
114
poly genetic-
-
79
113
ort/io-quinonoid -
-
83
160
para-quinorioicl -
-
83
113
quirionoid theory of
-
83
125
substantive
.
80
122
190
Eclipse colours
-
305
113
brown colours
-
313
94
yellow G, 3G
-
312
99
Emcraldino - olJ),
320,
322
97
Eosino -
-
188
96
Erachrome colours
.
114
98
Eriochlorine -
.
152
71
Eriochrome colours
.
114
red B -
132
93
Erio Chrome A/Airol B
.
176
46
Cyanine R -
-
175
49
Eriocyanino -
-
152
92
Erioglaucine -
-
152
48
Erythrincs
-
189
92
Erythrosines -
-
190
271
Erythrosine B
-
190
256
Esterification
-
68
122
Ethyl green -
-
149
246
Eurhodines -
256,
258
71
Eurhodoles
257,
258
172
105
F acid -
-
38
Fast Benzo orange S
-
124
137
black -
-
311
121
green -
-
92
133
Marine blue
-
249
135
yellow
-
104
135
Ferrocyanido blacks
-
318
115
Firms, List of Principal -
xiii
146
Flavanthreno'
-
224
80
Flavaurino
-
86
78
Flavazinos
-
131
266
Flavopurpurin 210,
212,
213
81
Fluorane
-
186
INDEX
333
Fluorescein -
Fluorescent blue
Formyl violets
Fuchsia -
Fuchsiasine -
Fuchsino (Magenta)
Fuchsono
Fuchsonimirio
Fulvene -
G acid -
Gallamine blue
Gallanil blue -
green
indigo
Galle'ine -
Galloeyanine -
Gallo violet -
Gambin G, Y, R -
Gamma acid -
Gentian blue -
Girofl6e -
Glacier blue -
Grenat soluble
Guaiacol
Guinea green B
H acid -
Helianthin
Helindone dyostuffs
blue 2B, 3G
Fast scarlet R
grey 2B, BR
orange D, R
pink BN -
rod B, 3B -
scarlet S
violet 2B -
violet D -
yellow 3GN
Holiochrysin -
Helio Fast red RL
Helvetia blue
Histizariii
Hoffmann's violet -
HoZo-quinones
Hydrazine yellows -
Hy drazobeiizen e
Jlydrazo-compounds
Hydrazones -
I'AOK
- 186
Hydron dyestuffs
PAGE
- 314
- 251
blue B, G, R
- 316
- 169
blue -black -
- 316
- 263
olive G
- 314
- 153
yellow G -
- 316
- 153
violet B
- 316
174, 175
Hydroquinone
35, 82
- 145
78
Immedial colours
- 305
black V
- 311
41
blue -
- 311
253, 254
bordeaux -
- 312
- 254
bronze
- 313
- 254
brown
- 313
- 254
Indono
- 309
- 190
maroon.
- 312
252, 253
orange C
- 312
- 253
Pure blue -
308, 309, 311
- 92
yellow D
- 312
- 65
yellow GG -
- 313
- 172
Imperial violet
- 171
- 263
Indamines
- 231
- 152
Indanthrene -
- 221, 222
- 87
colours
- 222
- 69
blue CE, GC
, GCD,
- 150
RC, RS -
- 222
blue 3G, 2GS
- 223
66
bordeaux B
- 229
- 105
dark blue BO
- 227'
- 294
golden orange
G, R - 227
- 294
green -
- 227
- 296
grey B
- 223
- 296
maroon
- 223
- 296
olive G
- 314
- 296
redG-
- 229
- 296
scarlet G
- 227
- 296
violet R
- 231
- 296
violet RT -
- 227
- 294
yellow
- 226
- 230
Indian yellow
- 105
- 133
Indican -
- 267
- 115
Indigo and Indigoid dye-
- 172
stuffs
- 266
- 202
Indigo, extraction of 267
- 168
gluten
- 269
- 236
industry
- 267
- 131
natural
- 266, 287
77
synthetic -
- 285, 286
54
vat
- 269, 274
- 129
white 269, 274, 275, 286
334
INDEX
Indigo brown
carmine
Pure B.A.S.F. -
yellow
yellow 3G Ciba -
" Indigo salt "
Zeuco-Indigo - 268,
Indigoid dyestuffs -
substituted
Indigotine
constitution of -
properties of
syntheses of
iso-Indigotiiio
Indirubine - 269,
Indocarbon S
Indogenides -
wo-Indogenides
Indol -
synthesis of
Indophenols -
Indophenol -
carbazol
Tndophenosafraniries
Indoxyl -
pseudo- Indoxy 1
Indulines
Induline 3B, 6B -
Ingrain dyestuffs -
Iodine violet -
Isamine blue -
Isatin -
psewdo-Isatin
Isatin yellow -
Isoanthraflavic acid
Isopurpuric acid
Isopurpurin - 210,
Isorosiridulines
J acid -
Jet black
Katigen colours
black 2B -
Ketone base -
Kryogen colours
brown
yellow G, R
Lactam structure -
PAGE
- 269
Lactim structure . -
PACE
272
- 269
Lakes -
79
- 286
Lake bordeaux B -
- 115
- 269
red D, P -
- 115
- 293
Lauth's violet 240,
241, 242
- 279
Leucaniline
- 155
269, 274
Leuco- bases -
- 147
- 289
Leuco-compounds -
77, 82
- 293
Liebermann and Kostaiioeki,
- 268
rule of
- 201
270, 273
Light blue
- 172
269, 288
green SF -
- 150
- 276
Fast yellows
- 131
- 276
Lithol Fast scarlet R
- 115
287, 288
red R -
- 115
- 316
Rubin B -
- 115
- 276
Lyons blue
- 171
- 276
- 271
Madder plant
- 203
- 272
Magdala rod -
- 263
- 237
Magenta
153, 165
- 238
constitution of -
- 154
- 315
dchappfe
158, 159
- 262
manufacture of -
- 157
- 275
properties of
- 163
- 275
Magenta OO -
- 160
257, 264
Magenta S
- 165
- 265
Malachite green
- 146
95, 301
derivatives of
- 149
- 168
homologues of
- 149
- 172
manufacture of -
- 147
270, 272
Manchester brown
- 106
- 272
yellow
' - 88
- 130
Martius yellow
88
- 202
Mauve -
1
87
Mauvei'no
259, 264
212, 213
pseudo-Mauveino
263, 264
- 257
Mauvemes
257, 263
Melanogen colours -
- 305
65, 66
Meldola's blue
- 248
- 120
Mercerol colours
- 114
Meri-quinorios
- 236
305
Meso-position
- 257
- 311
Motanilic acid
- 61
- 138
Metanil yellow
- 105
- 305
Methylene azure
- 246
- 313
Methylono blue
241, 242
- 313
use in analytical
chemistry
- 245
- 272
Methylene green -
- 246
INDEX
335
PAOK
Methylene violet - - 263
PAOK
New blue R - - - 249
Methyl green - - - 169
New Fast Cotton blue - 249
orange - - - 105
Magenta - - 161,165
violet- - - - 168
Methylene blue - - 246
Michler's hydrol - - 139
Methylene blue N.Q.G. 250
ketono - - - 138
Victoria blue - - 174
Mikado golden yellow - 133
yellow - 86, 104, 105
orange - - - 133
Nicholson's blue - - 173
yellow - - - 134
Night blue - - - 174
" Mixed acid" - - 44
Nigraniline - 319,321,322
Modern blue - - - 253
Nigrosines - - - 265
blue CVI - - - 253
Nile blue - - - 249
cyunincs - - -253
Nile blue A, 2B - - 250
heliotrope PH - - 253
Nitranilines 67
violet - ... 253
Nitration 43
violet N 253
practical details of - 44
Monoazo-dyestuffs - - 100
Nitroalizarins - 211
chrome-developed - 113
Nitrobenzene - - 45
Mordants - - - 79
Muscarine - - - 249
?so-Nitro-compounds - 90
Nitro-compounds,
reduction of - - 53
Naphtha 9
Nitro-dyestuffs - - 85
Naphthalene - - 12, 16
constitution of - 89
sulphonic acids 28
Acid black - - - 120
Nitronaphthalenes - - 48
Nitrophenols 50
greens - - - 152
aci-Nitrophenols 90
yellow 88
p-Nitrosodimothylaniline 93
Naphthazarin - - 204
Nitroso-dyestuffs - - 91
Naphthionic acid - 61,62
Nitrosonaphthols - - 92
a-Naphthol - - 36, 37
Nitrotoluenes - 47, 48
0-Naphthol - - 36, 37
N.W. acid - - - 39
Naphthol AS - - - 108
Napthol sulphonic acids - 37
Opal blue - - - 172
black - - ' - 120
Orange I. - - 108
blue - 248
II. - 109
blue-black - - - 118
III. .... 105
green 92
IV. - 105
yellow S - 88
No. 3 - - - - 109
Naphthyl blue - - 263
G - - ' - - 109
violet- - - - 263
Orcellino - - - 120
Naphthylamines - 59, 60
Orchil red A - - - 120
sulphonic acids - - 61
substitute - - 111
Naphthylamme black - 120
Orient yellow - - 190
yellow 88
Oxanthranol - - -221
a-Naphthylamme
Oxazimes - - 247
bordeaux - - 108
Oxazines ... 246
Naphthylone blue - - 249
Oxazones - - 247, 251
Neutral red - - - 258
Oxindigo - - - 296
violet- - - - 258
Oxindol - - 271, 272
No vile and Winther's acid 39
Oxonium theory - - lb*2
336
INDEX
Oxyanthraquinones
Oxyanthrarufin
Oxychrysazin
Oxyphenine -
Paeonine
Palatine Chrome black -
Paraleucaniline
Paranitrariiline red
Para red
Pararosanil ine
hydrochloride 156,
Paris violet -
Patent Biebrich black
blue -
blue A
Pen-position -
Perkin's violet
Permanent red 4B -
Persian blue -
Phenanthrono
Phenanthreno red -
Phenazonium derivatives
Phenetole
Phenocyanines
Phenol -
synthesis of
sulphonic acid
Phenolphthalein
Phenosafranino
Phenylene blue
brown
Phenylene diamines
Phenylglycine
Phenylhydrazones -
Phenyl violet
Phloxine
Phosphine
Phthalems
Phthalic anhydride
Phthalimide -
Phthalophenone
Picramic acid
Picric acid
Pigment colours
Fast red HL
orange R -
purple
scarlet 3B -
Polvchrorhin
PAGE
- 201
Polygenetic dyestuffs
PAGE
79
212, 213
Polymerisation black
320
- 212
Ponceaux
95
- 303
Ponceau G, 2G, 4GB, 2R,
3R, RT -
109
- 177
Primuline ...
298
c - 114
application of -
301
155, 156
manufacture of -
299
- 108
Prune -
254
67
Purpurin
212
155, 157
Purpuroxanthin
202
157, 164
Pyramino orange -
125
1
Pyranthrone -
226
- 120
Pyridono ring
230
- 150
Pyrocatechol -
35
- 151
Pyrogallocyanines -
253
- Ill
Pyrogen colours
305
1
blue R
311
- 115
Direct blue
311
- 266
green - - - -
312
- 18
olive - - - -
311
- 130
yellow M
311
yes 256
Pyrol colours -
305
69
Pyrono ring -
183
- 253
Pyronines
184
19
Pyronine B
185
- 35
G
184
- 32
- 177
Quinhydrone -
83
260, 261
Quinizarin - - 211,
214
- 235
Quinol - - - -
35
- 106
Quinone -
82
58, 123
^oZo-Quinones
236
- 282
meri- Quinones
236
- 129
Quinone-Tmide dyestuffs
233
- 171
Quinone -Oximes
91
- 190
Quinonoid theory of dye-
- 199
stuffs
83
178, 186
- 178
R acid - - - -
41
- 284
Radial yellows
132
- 178
Bed eorallin -
177
87
Reducing agents - 53,
270
86
Regina violet
171
- 114
Rosazurine
251
- 115
Resorcinol
35
- 115
Resorcin brown
116
- 115
yellow
104
- 115
Resorufamine
251
- 135
Resorufine
251
INDEX
Ilcxoll colours
PAGE
- 305
Succinems
PAGE
194
blacks
314
Sulphanilic acid
61
Rhodamines -
180, 191
Sulphide dyestuffs -
304
Rhodamiuc B
- 192
Sulpho-colours
305
313, 6G, S -
- 194
Sulphonation -
22
Roccollino
- 109
apparatus for
25
Kosaminos
- 185
practical details of
23
Rosanilino
154, 157
Sulphonic acids
22
hydrochlorido
150, 157
constitution of -
22
Rosanilines
- 165
manufacture of -
26
phonylaiod
- 169
Sulphur colours
305
llosaiithrono O
- 112
black T
311
Hose Bengal -
- 190
Sulphur dyestuffs -
304
Rosindulines -
- 257
constitution of
307
Rosolic acid -
176, 177
manufacture of
306
Rubcrythric acid
- 203
Sulphurised vat dyestuffs
314
Rufigallic acid
215
Sun yellow - - 133,
135
Russian green
- 92
Tannin, use as mordant -
79
Saccharei'ns -
- 194
Tannin heliotrope -
263
S acid -
- Ill
Tartar emetic, use of
80
Saf ratlines
- 257
Tartrazine - - 130,
131
Safranino
- 259
Tetrakisazo-compounds -
127
T
- 203
Tetrazo-compounda
121
Safranoles
- 257
coupling of -
124
Salicin colours
- 114
Thiazimes
241
Scarlet GR -
- 109
Thiazines - - 239,
241
Schaffor acid -
- 40
Thiazol dyestuffs -
298
Schollkopf acid
- Ill
yellow S
303
Sotocyanino -
- 152
Thiazones
241
Sotoglauciiie -
- 152
Thiazonium derivatives -
182
" Silver salt "
- 208
Thiocarmines
246
Single Bath black -
318, 321
Thioflavine T
303
Soluble blue XG -
- 172
Thiogen colours
305
Cotton blues
- 174
Thioindigo - - 290,
295
K os hies
- 189
Thioindigo B -
292
Primrose
- 190
grey 2B
296
Silk blue -
- 174
orange R -
296
Sky blue
- 172
pink BN -
296
Soudan III
- 120
red B -
292
brown
- 108
red 3B, BG
296
Spirit blue
- 172
scarlet R - - 288,
292
Eosines
- 189
scarlet S
296
Primrose -
- 190
violet 2B -
296
Sky blue
- 172
Thio Katigen colours
313
Steam blacks -
- 319
Thion colours
305
Stilbene dycstuffs -
- 133
brown
313
orange
- 134
yellow G
313
yellow 8G -
- 134
Thional colours
305
Substantive dycstuffs
80
bronze ...
313
338
INDEX
Thional brow r n G
Thionaphthoii
Thionine
Thionol colours
Thiophen
detection in benzene
Thiophor colours -
bronze G, 5G
Thioxin colours
Titan Comos -
Tolidine
Toluene -
Toluidines
Tolusaf rani no
Toluylene blue
Toluylenediamines -
Toluylene red
Triphenylmethane
stuffs
amido -derivatives
hydroxy-derivatives
Trisazo-dyestuffs
Tropseolin D -
O
30, 4O
Y
Turkey red oil
PAOK PAGB
- 313 Turmeric - - - 135
"- 290
Tyrian purple
294
- 241
- 305
Ultra violet dyestuffs
253
- 290
Uranine - - 18 7-,
188
no - 16
305
Vat dyestuffs
220
Ql'J
anthracene -
220
) A O
- 305
172
sulphurised
Verde Italiano
314
312
~ j. i j
1 99
Vesuvine -
106
1 ** t
10 14
Victoria blue -
174
A,Vf, It
58, 59
green 3B
152
263
orange
86
236, 255
59
Vidal black - - 304,
Violamine B, G, R, 2R -
311
193
255, 258
Violanthrene BS
227
dve-
Wurster's red
235
- 142
- 143
Xanthene dyestuffs
181
os - 176
Xanthone -
181
- 126
Xanthonium compounds
180
- 105
Xylene - - - 10
, 14
- 104
yellows
131
- 108
Xylidines
59
- 103
79
Yellow corallin
177
GLASGOW I PRINTKD AT TUB UNIVERSITY PRESS BY ROBERT MACI.KflOSR AMI) CO. LTD
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