Kinetics of the decomposition of bis-1,5-diphenylformazan-3-yl disulphide and bis-4-phenyl-Δ2-1,3,4-thiadiazolin-2-yl disulphide in organic solvents

Abstract

The heterolytic thermal fission of the sulphur–sulphur bond in the symmetrical disulphide bis-4-phenyl-Δ²-1,3,4-thiadiazolin-2-yl disulphide (I) to give the parent thiol (II) and a mesoionic compound (III) is shown to proceed by first-order kinetics and at rates which increase with the polarity of the solvent. Similar results are reported for bis-1,5-diphenylformazan-3-yl disulphide (IV) which is less stable and cleaves thermally to give equimolecular amounts of dithizone (1,5-diphenyl-3-mercaptoformazan)(VII) and a mesoionic compound (VIII) containing two fewer hydrogen atoms.

The mechanism is discussed and linear correlations demonstrated between log k and the polarity index Z for organic solvents or the index Y for reactions in ethanol–water mixtures.