Polyhalogenoaromatic compounds. Part XI. Some reactions of 2,3,5,6-tetrachloro-4-mercapto- and 2,3,5,6-tetrachloro-4-methylthiopyridine

Abstract

2,3,5,6-Tetrachloro-4-mercaptopyridine was prepared by treating pentachloropyridine with phosphorus pentasulphide or with potassium or sodium hydrogen sulphide. It could be methylated with dimethyl sulphate, and with n-butyl-lithium, after hydrolysis, it gave a mixture of 2,3,6-trichloro-(70%) and 2,3,5-trichloro-4-mercaptopyridine (30%) which could also be methylated. Oxidation of the tetrachloro-4-methylthiopyridine with peroxyacetic acid (1 or 2 equiv.) gave the 4-methylsulphinyl- and the 4-methylsulphonyl-pyridine respectively. Pyrolysis of the latter gave pentachloropyridine (45%), tetrachloro-4-methylpyridine (24%), and tar. With n-butyl-lithium the tetrachloro-4-methylthiopyridine yielded 4-n-butyltetrachloro pyridine as the major product, together with tetrachloro-4-mercaptopyridine and 2,3,5,6-tetrachloropyridine. The sodium salt of 2,3,6-trichloro-4-mercaptopyridine reacted with chloroacetone to give (2,3,6-trichloro-4-pyridylthio)acetone which cyclised on treatment with hot polyphosphoric acid to give 4,6,7-trichloro-3-methylthieno[3,2-c]pyridine.