Polyhalogeno-aromatic compounds. Part XXXII. Synthesis and some reactions of tetrachloropyridine-2-thiol and related compounds

Abstract

On reaction with thiourea or NN′-diethylthiourea, pentachloropyridine N-oxide gives bis(tetrachloro-2-pyridyl) disulphide from which tetrachloropyridine-2-thiol is obtained by reduction. This thiol is prepared less conveniently from tetrachloro-2-pyridyl-lithium and sulphur or by reaction of tetrachloro-2-nitropyridine with potassium hydrogen sulphide. The thiol has been converted into a number of derivatives. With potassium hydrogen sulphide, pentachloropyridine N-oxide gives either a mixture of tetrachloropyridine-2-thiol N-oxide, starting material, and polymer, or a mixture of the same thiol N-oxide and the 2,6-dithiol N-oxide, or the 2,6-dithiol N-oxide exclusively, depending on the amount of reagent used. Some reactions of the mono- and the di-thiol N-oxide are reported. Pentachloropyridine N-oxide gives tetrachloropyridine-4-thiol with phosphorus pentasulphide. Oxidation of tetrachloropyridine-4-sulphonyl chloride gives the corresponding N-oxide which reacts with dimethylamine to give NN-dimethyltetrachloropyridine-4-sulphonamide 1-oxide. Dimethyl 4,6,7-Trichlorothieno[3,2-c]pyridine-2,3-dicarboxylate has been prepared from lithium tetrachloropyridine-4-thiolate and dimethyl acetylenedicarboxylate.