A solution of 3,5-dimethylaniline (36.3 g; 0.3 mole) in glacial acetic acid (200 ml) is treated with methanesulfonic acid (60 g), and the stirred mixture cooled to 0°-5° C. in an ice-salt bath. An ice-cold solution of sodium nitrite (21 g in 80 ml H2O) is slowly added over a half-hour period. This diazonium solution is then added quickly to an ice-cold solution of cuprous chloride [from cooper sulphate 5 H2O (125 g), sodium chloride (32.5 g) and sodium sulphate (71 g)] in concentrated hydrochloric acid (160 ml). The mixture becomes very thick and is allowed to warm to room temperature. The stirring is continued overnight, and the solution is heated to 60° C. for 1/2 hour. Concentrated ammonia is added with cooling until the solution is alkaline, and the oil is extracted with ether. The dried ether extract distillation gives 5-chloro-m-xylene, b.p. 70°-73°/12 mm (25.6 g).
