Org. Synth. 1922, 2, 63
Submitted by Roger Adams and A. F. Thal.
Checked by O. Kamm and A. O. Matthews.
In a 5-l. round-bottom flask
, fitted with a mechanical stirrer
and reflux condenser
, are mixed 1150 cc. of water, 840 cc. of commercial sulfuric acid (Note 1)
and 700 g. (6 moles) of benzyl cyanide (p. 107)
. The mixture is heated under a reflux condenser and stirred for three hours (Note 2)
, cooled slightly, and then poured into 2 l. of cold water. The mixture should be stirred so that a solid cake is not formed; the phenylacetic acid
is then filtered off. This crude material is melted under water and washed by decantation several times with hot water. These washings, on cooling, deposit a small amount of phenylacetic acid
which is filtered off and added to the main portion of material. The last of the hot water is poured off from the material while it is still molten, and it is then transferred to a 2-l. Claisen distilling flask
and distilled under reduced pressure. A small amount of water comes over first and is rejected; about 20 cc., containing an appreciable amount of benzyl cyanide
, then distils. This fraction is used in the next run. The distillate boiling at 176–189°/50 mm.
is collected separately and solidifies on standing. It is practically pure phenylacetic acid
, m.p. 76–76.5°
, and weighs 630 g.
per cent of the theoretical amount) (Note 3)
. As the fraction which is returned to the second run of material contains a considerable portion of phenylacetic acid
, the yield actually amounts to at least 80
For the preparation of small quantities of phenylacetic acid, it is convenient to use the modified method given in (Note 3).
The standard directions for the preparation of phenylacetic acid
specify that the benzyl cyanide
is treated with dilute sulfuric acid
prepared by adding three volumes of sulfuric acid
to two volumes of water. The reaction, however, goes so vigorously that it is always necessary to have a trap
for collecting the benzyl cyanide
which is blown out of the apparatus. The use of the more dilute acid, as described in the above directions, is more satisfactory.
The odor of phenylacetic acid is disagreeable and persistent.
The phenylacetic acid
may also be made by boiling under a reflux condenser for eight to fifteen hours, without a stirrer, but this method is not nearly so satisfactory as that described in the procedure.
The following modified procedure can be used for the preparation of small quantities of the acid. One hundred grams of benzyl cyanide
is added to a mixture containing 100 cc. of water, 100 cc. of concentrated sulfuric acid
, and 100 cc. of glacial acetic acid
. After this has been heated for forty-five minutes under a reflux condenser, the hydrolysis is practically complete. The reaction mixture is then poured into water, and the phenylacetic acid
is isolated in the usual manner.
The standard method for the preparation of phenylacetic acid
is the hydrolysis of benzyl cyanide
with either alkali1
The acid hydrolysis runs by far the more smoothly and so was the only one studied. Phenylacetic acid
can also be prepared by the carbonation of benzylmagnesium chloride3
and by the catalytic reduction of mandelic acid
This preparation is referenced from:
Chemical Abstracts Nomenclature (Collective Index Number);
sulfuric acid (7664-93-9)
acetic acid (64-19-7)
Mandelic acid (90-64-2)
α-Toluic acid (65-85-0)
Benzyl cyanide (140-29-4)
Phenylacetic acid (103-82-2)
benzylmagnesium chloride (6921-34-2)
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