To a mixture of
212 g. (1 mole) of benzoin (Note
1),
200 cc. of glacial acetic acid, and
200 cc. (2.1 moles) of acetic anhydride, in a
1-l. beaker provided with a
mechanical stirrer, is added slowly, with stirring,
20 cc. of concentrated c.p. sulfuric acid. This requires five minutes, during which the
benzoin quickly dissolves and the temperature rises to about 50°. The beaker is placed on the
steam bath for twenty minutes (Note
2). The mixture is allowed to cool somewhat, transferred to a
large dropping funnel, and added
slowly to 2.5 l. of water vigorously stirred in a
4-l. (1-gal.) crock during thirty minutes (Note
3). Stirring is continued for one hour. The mixture is filtered by suction on a
30-cm. Büchner funnel, and the crystals are sucked as dry as possible and spread on
filter paper. After about two hours the crystals are transferred to a 1-l. beaker and warmed to about 60° with
400 cc. of 95 per cent ethyl alcohol. The clear solution is cooled with stirring to 5° and filtered by suction. The air-dried
benzoin acetate, melting at
80–82°, weighs
220–230 g. (
86 to 90 per cent of the theoretical amount). Another crystallization from
400 cc. of alcohol removes the slight yellow tinge and gives a product melting at
81.5–82.5°, with a loss of about 10 g.