Surface-mediated reactions.: 8.: Oxidation of sulfides and sulfoxides with tert-butyl hydroperoxide and OXONE

Silica gel and alumina have been found to mediate the oxidation of sulfides and sulfoxides with (CH3)(3)COOH and OXONE. With all combinations except (CH3)(3)COOH/alumina, sulfides were oxidized with reasonably good selectivity to sulfoxides. These studies afforded insights into the mechanisms of surface-mediated processes. Adsorption studies, combined with the effect of partial silylation of silica gel, indicate that oxidation of sulfides by (CH3)(3)COOH/silica gel occurs at least predominantly via nucleophilic attack by the sulfide on (CH3)(3)COOH which is activated by being bound to isolated silanol sites on the silica gel surface (Scheme 2), whereas oxidation of sulfoxides involves nucleophilic attack by (CH3)(3)COOH on the sulfoxide, which is activated by being bound to associated silanol sites (Scheme 3). Oxidation of sulfoxides by (CH3)(3)COOH/alumina involves attack of (CH3)(3)COO- on the sulfoxide bound to free Al+ sites on the surface (Scheme 4B). Mediation of oxidation by OXONE involves instead activation by its being dispersed on the surface of the adsorbent, providing contact between KOSO2OOH, the oxidizing component, and the substrate. With silica gel, binding involves the associated silanol sites (Scheme 5). It is proposed that this is a general model for surface mediation of inorganic salts.