Surface-Mediated Reactions. 8. Oxidation of Sulfides and Sulfoxides with tert -Butyl Hydroperoxide and OXONE 1

Silica gel and alumina have been found to mediate the oxidation of sulfides and sulfoxides with (CH 3 ) 3 COOH and OXONE. With all combinations except (CH 3 ) 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 (CH 3 ) 3 COOH/silica gel occurs at least predominantly via nucleophilic attack by the sulfide on (CH 3 ) 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 (CH 3 ) 3 COOH on the sulfoxide, which is activated by being bound to associated silanol sites (Scheme 3). Oxidation of sulfoxides by (CH 3 ) 3 COOH/alumina involves attack of (CH 3 ) 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 KOSO 2 OOH, 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.