In a 2-l. round-bottomed flask, fitted with a stopper holding a dropping funnel and a mechanical stirrer, is placed a mixture of 275 cc. (4.3 moles) of concentrated nitric acid (sp. gr. 1.42) (Note 1) and 275 cc. (4.9 moles) of concentrated sulfuric acid (sp. gr. 1.84). This is cooled to 10° in a freezing mixture, and 100 g. (0.85 mole) of benzyl cyanide (free from alcohol and water) (Note 2) is run in slowly, at such a rate that the temperature remains at about 10° and does not exceed 20°. After all the benzyl cyanide has been added (about one hour), the ice bath is removed, and the mixture is stirred for one hour and then poured onto 1200 g. of crushed ice. A pasty mass slowly separates; more than half of this mass is p-nitrobenzyl cyanide, the other constituents being o-nitrobenzyl cyanide, and a variable amount of an oil which resists hydrolysis; apparently no dinitro compounds are formed. The mass is filtered on a porcelain funnel with suction, pressed well to remove as much oil as possible, and dissolved in 500 cc. of boiling 95 per cent alcohol. On cooling, p-nitrobenzyl cyanide crystallizes; the mother liquor, on distillation, gives an impure alcohol which can be used for the next run. Recrystallization from 550 cc. of 80 per cent alcohol (sp. gr. 0.86 to 0.87) yields 70–75 g. (50–54 per cent of the theoretical amount) (Note 3) of a product which melts at 115–116°.

This product is satisfactory for most purposes, and incidentally for the preparation of p-nitrophenylacetic acid (p. 406). Occasionally it must be free even from traces of the ortho compound; if so, it should be crystallized again from 80 per cent alcohol; it then melts at 116–117°.