A solution of 390 g. (3 moles) of aniline hydrochloride and 190 g. (3.2 moles) of urea in 1500 cc. of water is boiled in a 3-l. flask under a reflux condenser (Note 1) and (Note 2). After about one hour, crystals begin to separate; at the end of one and one-half to two hours, the mixture, which bumps considerably, is filtered rapidly by suction, and the crystals of carbanilide washed with 100 cc. of boiling water. The filtrate is chilled, and the phenylurea which crystallizes out is filtered off and rinsed with a little cold water, the washings being discarded. The filtrate is again boiled under a reflux condenser for one and one-half to two hours, or until it begins to bump, and the process is repeated. The above operations are repeated a third time, and each time the phenylurea is collected from the cold filtrate. The mother liquor is finally evaporated to one-half its original volume, and additional crops of carbanilide and phenylurea are so obtained. Further evaporation is not profitable.

The crude carbanilide (symmetrical diphenylurea) is practically pure, and may be obtained in large colorless needles melting at 235° by recrystallization from alcohol with the use of decolorizing carbon; 1 l. of alcohol is required for every 25 g. of product (Note 3). The weight of the crude carbanilide is 122–128 g. (38–40 per cent of the theoretical amount).

The crude phenylurea is somewhat colored and contains a little carbanilide. It may be purified by dissolving in a minimum quantity of boiling water, adding a little decolorizing carbon, and filtering. When the filtrate first begins to cool, a flocculent precipitate of carbanilide is deposited; this must be filtered off while the liquid is still hot. The filtrate, on cooling, yields colorless stout needles or flakes of phenylurea melting at 147° (Note 4). The total weight of pure product is 212–225 g. (52–55 per cent of the theoretical amount).