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 _in vacuo_. 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 176-189'0/50 mm.
is collected separately and solidifies on standing. It is practically
pure phenylacetic acid, m. p. 76-76.5'0; it amounts to 630 g.
(77.5 per cent of the theoretical amount). 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 per cent.

For the preparation of small quantities of phenylacetic acid,
it is convenient to use the modified method given in the Notes.


2. Notes

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,