140 (H'ALITATIVE ORGAXIC ANALYSIS
the isolation of the anhydrous acids when present in low concentrations is
not a convenient operation.
The met hot! is of importance not merely in connection with the identi-
nVation of the eight comixiunds listed, but of any compounds that are readily 1
converted into ihe>e acids, e.g., the esters, amides, nitrites, salts, etc. It is
of rtrurse necessary that the total acidity of the solution be due entirely to
the volatile acid present and not to inorganic acid.
(hitline the method for the identification of propionic acid in the solution
obtained by the alkali hydrolysis of propionamide.
ESTERS, ALDEHYDES, AND KETONES
EXPERIMENT 17
Determine the specific gravity at 20° of ethyl benzoate in one i
of the small specific gravity tubes (cap. about f cc.). See page
119, Fig. 10.
Dissolve 2 g. of sodium in 50 cc. of absolute alcohol and add
10 cc. of water after the sodium has dissolved. Withdraw a 10-cc. |
sample from the homogenous solution for titration against N/4 1
acid for a determination of alkalinity. Place 40 cc. of the remain-
ing alkaline solution into a 100 cc. r.b. flask and transfer quan-
titatively from the specific gravity tube the weighed sample of
ester. This may be done by means of the capillary tube used for
filling the bulb. Small portions of the alcohol from the 40-cc. {
portion of sodium ethylate solution are used for the purpose of
rinsing the tube.
Boil the ester solution under the reflux for one-half hour, cool
the contents of the flask, withdraw a 10 cc. portion of the alcoholic *
solution and titrate the excess alkali against the N/4 acid. From i
these values the saponification equivalent of the ester may be
determined by the use of a formula identical with that used for
calculating neutral equivalents of acids.
Q .- ,. . , , Wt. of esterX1000
bapomfication equivalent=^----------^-^—=n—^------?.
No. cc. of N alkali used .• fc
The specific gravity tube is convenient for weighing samples intended
for quantitative saponification, since a single trip to the balance serves not
only for weighing the sample, but also for an accurate determination of the
specific gravity—a constant which may prove of value in connection with the f
identification of the unknown. - *_
For esters of low molecular weight, the quantity of sodium used must
be increased accordingly.