(A) Preparation of Cuprous Chloride Solution (Note 1).—A solution of 1250 g. (5 moles) of crystallized copper sulfate and 325 g. (5.6 moles) of sodium chloride in 4 l. of hot water is prepared in a 12-l. flask. The flask is fitted with a mechanical stirrer, and an alkaline solution of sodium sulfite (265 g. of sodium bisulfite and 175 g. of sodium hydroxide in 2 l. of water) is added during a period of five to ten minutes. The mixture is allowed to cool to room temperature and washed by decantation. The cuprous chloride is obtained as a white powder, which, however, darkens on exposure to the air. The crude product is dissolved in 2 kg. of commercial 28 per cent hydrochloric acid (sp. gr. 1.14) and the solution is used in the following preparation (Note 2).

(B) o-Chlorotoluene.—In a 10-l. stone jar fitted with a mechanical stirrer are placed 2 kg. (1755 cc.) of commercial 28 per cent hydrochloric acid (sp. gr. 1.14) and 428 g. (427 cc., 4 moles) of o-toluidine. The mixture is cooled to 0° by adding cracked ice (about 1 kg. is required). The o-toluidine hydrochloride separates as a finely divided precipitate. The stirrer is started, and to the cold suspension is added a solution of 280 g. (4.05 moles) of sodium nitrite in 800 cc. of water; the diazotization is carried out at 0–5° and requires about fifteen minutes. Cracked ice is added from time to time to keep the temperature within the proper limits. The volume of the final solution is 5–6 l.

While the diazotization is being carried out the cuprous chloride solution (A) is cooled to 0°. The cold diazonium solution is now poured rapidly into the well-stirred cuprous chloride solution. The solution becomes very thick, owing to the separation of an addition product between the diazonium salt and the cuprous chloride. The cold mixture is allowed to warm up to room temperature, and stirring is continued for two and one-half to three hours at this temperature (Note 3). When the temperature reaches about 15°, the solid addition compound begins to break down with the formation of nitrogen and o-chlorotoluene. After the specified time the solution is placed on a steam bath and heated to 60° to complete the decomposition of the addition product. The o-chlorotoluene forms a layer on top of the copper salt solution. The water solution is drawn off through a siphon until only 5–6 l. remains. The remaining material is steam-distilled from a 12-l. round-bottomed flask (Note 4) until about 3.5–4 l. is collected in the distillate. The o-chlorotoluene layer is separated from the water, washed with cold concentrated sulfuric acid (Note 5) and then with water, and finally dried over calcium chloride. The product boiling at 155–158° weighs 375–400 g. 74–79 per cent of the theoretical amount).

(C) p-Chlorotoluene.—p-Chlorotoluene is prepared in exactly the same way starting with p-toluidine. The yields are 70–79 per cent of the theoretical amount of a product which boils at 158–162° and melts at 4–7°.