In a 1-l. three-necked flask fitted with a stirrer, a thermometer, and a dropping funnel are placed 300 ml. of water and 55.5 ml. of concentrated hydrochloric acid. The flask is surrounded by an ice-salt bath, the stirrer is started, and 33.5 g. (0.31 mole) of phenylhydrazine (Note 1) is added dropwise (5–10 minutes is required). Phenylhydrazine hydrochloride separates as fine white plates. Stirring is continued, and, after the temperature has fallen to 0°, 100 ml. of ether is added, after which a previously prepared solution of 25 g. of technical sodium nitrite in 30 ml. of water is added from the dropping funnel at such a rate that the temperature never rises above 5°. This requires 25–30 minutes.

The reaction mixture is subjected to steam distillation until about 400 ml. of distillate is obtained. The ether layer is removed from the distillate, and the aqueous layer is extracted once with 25 ml. of ether. The combined ethereal solutions are dried over 10 g. of anhydrous calcium chloride. The dried solution is placed in a 200-ml. ordinary Claisen flask arranged for vacuum distillation. The flask must be surrounded by a cylindrical wire screen, and a laminated glass screen must be interposed between the operator and the apparatus (Note 2). The flask is immersed in a water bath at 25–30°, and the ether is removed under reduced pressure. Then the temperature of the water bath is raised to 60–65°, and the product is distilled under reduced pressure. Phenyl azide boils at 49–50° at 5 mm. (Note 3). A yield of 24–25 g. (65–68%) of the pungent, pale yellow, oily azide is obtained (Note 4).