芳香重氮盐和氰化亚铜反应可得到氰基化合物，该反应要在中性条件下进行，以避免氰化氢的逸出。通常在制备好重氮盐后，用NaHCO3或Na2CO3小心地将体系中和到中性。反应产率一般，有时候用氰化镍代替氰化亚铜，可以得到较好的产率。

   (A) Preparation of Cuprous Cyanide Solution. —Cuprous chloride prepared from 1250 g. (5 moles) of crystallized copper sulfate, according to the directions given on p. 170, is suspended in 2 l. of cold water in a 15-l. crock fitted with a mechanical stirrer. A solution of 650 g. (12.7–13 moles) of sodium cyanide (96–98 per cent) in 1 l. of water is added and the mixture stirred, whereupon the cuprous chloride enters into solution with considerable evolution of heat.  Surrounding the crock with cold water then cools the mixture. 

    (B) o-Tolunitrile. —While the cuprous cyanide solution is cooling, 428 g. (427 cc., 4 moles) of o-toluidine is mixed in a 20-l. crock with 1 l. of commercial 28 per cent hydrochloric acid (sp. gr. 1.14) and enough cracked ice, about 4 kg to bring the temperature of the mixture to 0°. A solution of 280 g. (4.06 moles) of sodium nitrite in 800 cc. of water is added, with stirring, to the resulting suspension of o-toluidine hydrochloride, the temperature being kept at 0–5° by the addition of cracked ice. The addition of the nitrite occupies about fifteen minutes; at the end of the operation, the mixture must show a distinct and permanent reaction for free nitrous acid on testing with starch-iodide paper. The final volume of the solution is 5–6 l. The mixture is now cautiously neutralized by adding dry sodium carbonate with constant stirring, using litmus paper to determine the end-point; about 200 g of the anhydrous carbonate is required. 

    The cold cuprous cyanide solution is now chilled to 0–5° by the addition of ice, and 1 l. of benzene is poured on the surface. To this mixture is slowly added the cold neutralized diazonium solution. During the addition, which occupies about thirty minutes, such vigorous stirring is maintained that the benzene on the surface is constantly drawn to the stirrer, and the temperature is maintained at 0–5° by occasionally adding ice. As soon as the diazonium solution comes into contact with the cuprous cyanide, a dark yellow, oily precipitate is formed that at once begins to give off nitrogen; the resulting nitrile is taken up by the benzene as soon as it is formed. When all has been added, the temperature is held at 0–5° for thirty minutes longer, and then is allowed to rise to that of the room (20–25°), which usually requires about three hours. 

      After stirring has been continued for two hours longer, the crock is surrounded by hot water or steam and warmed to 50° without stirring. The mixture is then allowed to stand until cool, when the aqueous layer is drawn off by means of a siphon. The upper oily layer is transferred to a 12-l. flask and distilled in a current of steam until no more oil passes over; about 10 l. of distillate is collected. The water is drawn off and the benzene removed by distillation, by means of a 2-l. round-bottomed flask and a fractionating column about 90 cm. long. When benzene no longer distils over,the distillation is continued in the same apparatus under reduced pressure, and the fraction that boils at 94–96°/20 mm. is collected. A small amount of dark-colored residue remains in the flask. The yield of almost colorless o-tolunitrile is 300–330 g. (64–70 per cent of the theoretical amount).