The standard directions for the preparation of phenylacetic acid
specify that the benzyl cyanide is to be treated with dilute
sulfuric acid prepared by adding three volumes of sulfuric acid
to two volumes of water. There action, 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 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.
When only small quantities of the acid are required, the following
modified procedure is of value. One hundred grams of benzyl cyanide
are 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 isolated in the usual manner.
The odor of phenylacetic acid is disagreeable and persistent.