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. (
77.5 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 per cent.