HETEROCYCLIC POLYFLUORO-COMPOUNDS .15. SYNTHESIS OF TETRAFLUOROPYRIDINE-4-SULPHONIC ACID AND RELATED SULPHUR-CONTAINING DERIVATIVES OF PENTAFLUOROPYRIDINE

Pentafluoropyridine reacts with potassium hydrosulphide, potassium thiophenoxide, sodium benzenesulphinate, or sodium sulphite in aprotic solvents to yield 2,3,5,6-tetrafluoropyridine-4-thiol, phenyl 2,3,5,6-tetrafluoropyridyl sulphide, phenyl 2,3,5,6-tetrafluoropyridyl sulphone, and 2,3,5,6- tetrafluoropyridine-4-sulphonic acid, respectively. Reaction of sodium 2,3,5,6-tetrafluoropyridine-4-sulphonate with sodium cyanide in dimethylformamide gives 4-cyano-2,3,5,6-tetrafluoropyridine. Treatment of 2,3,5,6-tetrafluoropyridine-4-thiol with pentafluoro-pyridine, cyanuric chloride, or performic acid yields bis-(2,3,5,6-tetrafluoropyridyl) sulphide, dichloro-s-triazinyl 2,3,5,6-tetrafluoropyridyl sulphide, and 2,3,5,6-tetrafluoropyridine-4-sulphonic acid, respectively. Oxidation of phenyl 2,3,5,6-tetrafluoropyridyl sulphide with hydrogen peroxide yields phenyl 2,3,5,6-tetrafluoropyridyl sulphone and the corresponding sulphoxide; bis-(2,3,5,6-tetrafluoropyridyl) sulphoxide and sulphone are formed when the corresponding sulphide is treated with peroxytrifluoroacetic acid. Chlorination of bis(2,3,5,6-tetrafluoropyridyl)disulphide, obtained by oxidation of the parent thiol with bromine, yields 2,3,5,6-tetrafluoropyridine-sulphenyl chloride, which reacts with piperidine to give the corresponding sulphenamide.