Submitted by Carl N. Webb
Checked by C. S. Marvel and P. L. Salzberg.
1. Procedure
In a
3-l. round-bottomed flask are placed
750 g. (8.1 moles) of aniline (Note
1) and
1 kg. (8.2 moles) of benzoic acid. When about two-thirds of the
benzoic acid is in the flask the mixture is melted to make room for the rest. The flask is placed in a large
oil bath and connected to a
condenser for distillation. The temperature of the oil is raised quickly to 180–190°, at which point distillation starts. The bath is held at this temperature until practically no more
aniline and water distil (about two hours), and then the temperature is slowly raised to 225° and maintained at this temperature until no further distillation takes place (one to two hours). The oil bath is now removed and the contents of the flask are allowed to cool below 180° and
550 g. (5.9 moles) of aniline is added. The distillations at 190° and 225° are repeated (about six hours). The hot mixture is poured into two
20-cm. evaporating dishes (Hood) and is allowed to cool. The crude product weighs
1600–2000 g., depending on the amount of
aniline retained.
The purplish-gray solid is ground (Note
2) in a large
mortar and is poured with vigorous stirring into a
12-l. (3-gallon) crock containing
6 l. of approximately normal hydrochloric acid (5.5 l. of water and
500 cc. of concentrated hydrochloric acid). The stirring is continued for one hour after all the
benzanilide has been added, and then the solid is filtered on a
20-cm. Büchner funnel. The process of stirring with acid and filtering is repeated twice to remove the excess of
aniline. The solid is stirred for two hours with 6 l. of water and is filtered. It is stirred for one hour with
6 l. of normal sodium hydroxide solution to remove the excess of
benzoic acid and is then filtered. The stirring with alkali and filtering is repeated. The solid is next stirred for two hours with 7 l. of water and is filtered, sucked dry, and air-dried overnight on paper.
After drying on paper the purplish solid is dried to constant weight in three 20-cm. evaporating dishes at 90–100° (about two days) and is then repowdered. The product is light purplish-gray and weighs
1270–1325 g. (
80–84 per cent of the theoretical amount). It melts at
157–160°. The product is pure enough for use in the preparation of
p-dimethylaminobenzophenone (p. 217) and for most synthetic purposes. When
100 g. of benzanilide is dissolved in
750 cc. of hot alcohol (Note
3) and the solution is boiled with about
10 g. of decolorizing carbon (Norite), filtered, and cooled at 10° overnight,
80–86 g. of an almost colorless product melting at
160–161° separates. A second crystallization from alcohol using decolorizing
carbon gives a white product with approximately the same loss in the mother liquors as in the first crystallization.
2. Notes
3. Discussion
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