water-bath with a condenser for about half an hour. On cooling the liquid, benzoin separates out as a mass of small colourless crystals, which are filtered off from the mother liquor. From the latter a further quantity of benzoin may be obtained by adding 2-3 grms. potassium cyanide and again heating for a short time. on the water-bath. The second crop of crystals is added to the first and the whole recrystallised from hot alcohol.

Properties.-Colourless prisms; m. p. 137°; with difficulty soluble in water; easily soluble in alcohol and ether. The solution in dilute alcohol reduces Fehling's solution on warming. On oxidation with nitric acid it yields benzil, C&H,CO CO C6H5

Fifteen grms. benzoin are heated on the water-bath with 35 grms. conc. nitric acid in a flask connected with an air condenser, the flask being well shaken. Nitrous fumes are evolved and the crystals of benzoin are converted into a yellow oil, which after two hours heating is free from unchanged benzoin. After oxidation the contents of the flask are poured into water and the yellow crystalline deposit separated by filtra

Properties.-Yellow prisms; m. p. 95°; insoluble in water, easily soluble in hot alcohol and ether; dissolves in cold alcoholic potash solution with a violet colour.

PREPARATION XXVII.

BENZILIC ACID, C11H12O3=(C6H5)2C(OH)·CO2H. (Diphenylglycolic Acid.)

LITERATURE.-Liebig (1838), Ann. Ch. Pharm. 25, 25; Zinin (1839), Ann. Ch. Pharm. 31, 329; E. Fischer (1880), Ber. 14, 326.

Fifty grms. caustic potash are melted with a small quantity of water in a silver crucible on the oil-bath. The temperature of the mass is brought to 150° and 10 grms. finely powdered dry benzil added. The benzil melts and the contents of the crucible shortly change to a solid mass of potassium benzilate. The cooled melt is dissolved in water and the alkaline

solution acidified with hydrochloric acid, which precipitates the benzilic acid.

The crystalline mass, which contains small quantities of benzoic acid, is separated from the mother-liquor and washed with cold water. It is then transferred to a porcelain basin, dissolved in hot water and the solution boiled until the smell of benzoic acid has entirely disappeared. On cooling, benzilic acid crystallises out and is purified by a second crystallisation from hot

water.

C6H5CH(OH)
C&H,CO

Benzil

+ KOH = (C6H5)2COH.COOK

Potassium Benzilate.

Properties.-Colourless needles; m. p. 150°; scarcely soluble in cold, readily in hot water and alcohol; dissolves in conc. sulphuric acid with an intense red colour.

PREPARATION XXVIII.

BENZOYL CHLORIDE, C,H,OC1=C,H,COCI.

LITERATURE.-Wöhler (1832) Ann. Ch. Pharm. 3, 262; Cahours (1846), Ann. Ch. Pharm. 60, 255, and (1849), 70, 40.

The pentachloride may also be used, in which case three times the quantity must be taken. The reaction is started by

Fifty grms. dry benzoic acid are introduced into a flask connected with a spiral condenser and 30 grms. phosphorus trichloride are added.* When the reaction which proceeds at the ordinary temperature is finished, the contents of the flask are heated on the oil-bath to 120° until the evolution of hydrochloric acid ceases. The benzoyl chloride is obtained from the liquid product by distillation. Unchanged phosphorus trichloride first passes over, the thermometer then rises to 195° and benzoyl chloride begins to distil. The latter after a second distillation is chemically pure.

3C6H5CO2H + PCI,
Benzoic Acid

=

3C6H5COCI + P(OH)3
Benzoyl Chloride.

Properties.-Colourless liquid with a penetrating odour; b. p. 198°5°; sp. gr. 1°2142 at 19°; decomposes with water forming hydrochloric acid and benzoic acid. With ammonia it yields benzamide (C,H,CONH,).

Benzamide.-5 grms. benzoyl chloride.

Five grms. benzoyl chloride are slowly added to 10 grms. finely powdered commercial ammonium carbonate and thoroughly mixed in a mortar. The reaction proceeds quietly. If the smell of benzoyl warming, and is complete when the benzoic acid has dissolved. Hydrochloric acid is evolved, and phosphorus oxychloride formed, the latter being removed by fractional distillation.

chloride does not entirely disappear, the mass is heated for about twenty minutes on the water-bath or a few drops of strong aqueous ammonia added. It is allowed to cool, extracted with cold water and filtered. The benzamide remains on the filter in the form of a white crystalline powder, and may be recrystallised from a small quantity of boiling water.

C6H5COCI + 2NH3 = C6H5CONH2 + NHCI
Benzoyl Chloride

Benzamide.

Properties. Colourless plates; m. p. 128°; b. p. 290°; scarcely soluble in cold, more readily in boiling water; soluble in alcohol and ether.

PREPARATION XXIX.

NHCH

SULPHOCARBANILIDE, C13H12N2S-CSNHCH

(Diphenylthiourea, Thiocarbanilide.)

LITERATURE.-Hofmann (1849), Ann. Ch. Pharm. 70, 142; Weith (1873), Ber, 6, 967; Losanitsch (1886), Ber. 19, 1821.

100 grms. aniline

A solution of 100 grms. pure commercial aniline, 50 grms. carbon bisulphide,' and 50 grms. absolute

1 Carbon bisulphide being very volatile and exceedingly inflammable, great care must be taken when using this substance in the neighbourhood of a flame.