ELECTROCHEMICAL REDUCTION OF 2,5-DICHLOROBENZENESULFONYL CHLORIDE AND CORRESPONDING DISULFIDE

The electrochemical reduction of 2,5-dichlorobenzenesulphonyl chloride to the corresponding thiol proceeds at high material and current efficiencies (90-100%) on a lead cathode in organic and aqueous organic solvents. Sulpholane/hydrochloric acid or ethanol/sulphuric acid electrolytes appear suitable media for the reaction. Disintegration of the lead cathode was observed in the presence of chloride ions upon prolonged operation but this may be avoided using an alternative electrochemical/chemical process based on the reaction between the thiol and the sulphonyl chloride to produce disulphide. The disulphide may then be reduced electrochemically to the thiol, the latter being used for recycle. This route is also an effective means to circumvent the hydrolysis of the starting material to the corresponding sulphonic acid, which is reduced only with great difficulty, and its formation constitutes an inefficiency in the total process and introduces a by-product that increases process costs. To whom all correspondence should be addressed. © 1979 Chapman and Hall Ltd.