E.s.r. spectroscopy has been employed to characterize radical pathways in the thermal and photolytic decomposition of a variety of diaryl sulphoxides and aryl arenethiolsulphonates (ArS0,SAr). For the sulphoxides, S-C bond cleavage leads to the formation of the delocalized and relatively unreactive sulphinyl radicals (ArSO.) ; their subsequent reaction evidently involves disproportionation to sulphonyl (ArSO,.) and thiyl (ArS.) radicals. This pair of radicals is also formed directly in the homolysis of the thiolsulphonates, and the subsequent formation of sulphinyl radicals has been investigated. The results are analysed in terms of the products of the reactions and the efficacy of some of the parent substrates as antioxidants.

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The aryl sulphides 3,3',5,5'-tetra-t-butyl-4,4'-dihydroxydiphenyl sulphide (1 ), the corresponding disulphide (2). trisulphide (3). and tetrasulphide (4). and the alkyl sulphides di-t-butyl sulphide (7) and dibenzyl disulphide (1 0) have been used to catalyse the decomposition of I -methyl-1 -phenylethyl hydroperoxide (cumene hydroperoxide) a t 393 K. The decompositions are catalytic pseudo-first-order reactions. The kinetic data and product studies demonstrate that the catalyst for hydroperoxide decomposition is sulphur dioxide. The mechanism for formation of the sulphur dioxide has been demonstrated to involve oxidation of the sulphides and decomposition of the resulting thermally unstable sulphur-oxygen compounds. The results demonstrate that the thermal chemistry of sulphur-oxygen compounds (sulphoxides. thiolsulphinates, etc.) formed from the sulphides determines whether or not the sulphide will catalyse hydroperoxide decomposition. RESULTS AND DISCUSSIONAt 393 K the aryl sulphides (1)-( 4), the sulphoxide (5), the thiolsulphonate (6), di-t-butyl sulphide (7), di-

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