The chlorination of pyridine: Investigations on pyridine and quinoline derivatives 41st. Communication

Abstract On chlorinating pyridine in the gas phase at 270° a good yield of 2‐chloropyridine is obtained together with a small quantity of 2:6‐dicloropyridine. At 400° the main product is 2:6‐dichloropyridine. It is shown that among the products produced in the chlorination at 270°, a small amount of a pyridylpyridinium compound must be present, for 2‐aminopyridine is obtained on hydrolysis of the reation product. Chlorination in the gas phase takes place very slowly at about 200° at this temperature 3:5‐dichloropyridine is obtained together with 3:4:5‐trichloropyridine. On chlorinating fused pyridine hydrochloride at about 170° a considerable yield of 3:5‐dichloropyridine is produced along with a small amount of 3:4:5‐trichloropyridine and pentachloropyridine. Thus in the chlorination of pyridine a specific temperature effect on the type of substitution is observed as in the bromination of pyridine. In the chlorination, the temperature limits for both types of substitution lie near together. 2‐Aminopyridine is obtained on heating 2‐chloropyridine with aqueous ammonia and copper sulphate. 2‐Amino‐6chloropyridine is obtaines on heating 2:6‐dichloropyridine with aqueous ammonia.