摘要：

The oxidation of thiols by four transition metal oxides has been studied in xylene at 55deg; in the absence of oxygen. In all cases studied, oxidation of the thiol to its disulfide was observed. The most active metal oxide was manganese dioxide. Ferric oxide, cobaltic oxide, and cupric oxide displayed similar oxidizing capabilities. Product yields and rate studies indicate that thiol structure and acidity do not influence the rate of thiol conversion. The reactions are not influenced by the presence of amine catalysts but they are dependent on the rate of agitation. These facts suggest that the rate-determining step in these reactions is thiol adsorption on the surface of the metal oxide. Oxidation studies at various thiol-metal oxide ratios in the presence of an olefin resulted in the formation of sulfide. The latter apparently forms by a low-temperature, free-radical addition reaction in which the metal oxide functions as an initiator for the production of thiyl radicals. This finding represents the first unequivocal evidence for the production of intermediate free radicals in low-temperature oxidations by manganese dioxide and other transition metal oxides.

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