Addition of hydrogen cyanide to an aldehyde. Mandelic acid from benzaldehyde

ADDITION OF HYDROGEN CYANIDE TO AN ALDEHYDE. MANDELIC ACID FROM BENZALDEHYDE 

Mandelic Nitrile.—Freshly distilled benzaldehyde (15 g.) is stirred with a glass rod in a cylinder with about 50 c.c. of a concentrated solution of sodium bisulphite until a paste of the addition compound /H 

C -OH has formed. The cylinder is then closed with a XSOsNa 

Hydrolysis of the Nitrile.—The nitrile, mixed in a porcelain basin with four times its volume of concentrated hydrochloric acid, is heated on the water bath until an abundant separation of crystals begins to take place on the surface of the liquid. The reaction mixture is then allowed to stand over night in a cool place, and the crystals which have been deposited, after being rubbed with a little water, are separated at the filter pump and washed with water (not too much). A further quantity of the acid is obtained from the filtrate by extraction with ether. The crude mandelic acid is pressed on a porous plate, dried, and purified by crystallisation from benzene. Melting point 118°. Yield about 10-15 g. 

Pure Z-mandelic acid is not easily obtained from small amounts of 1 Cf. Ber., 1883, 16, 1773 and 1899, 32, 2385. 

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