Selective and mild oxidation of sulfides to sulfoxides by oxodiperoxo molybdenum complexes adsorbed onto silica gel

Aliphatic and aromatic sulfides, ketosulfides, sulfinyl acids and esters, and olefinic sulfides were oxidized to sulfoxides using oxodiperoxo complexes of molybdenum coated on silica gel (150 Å pore size) in very high yields. Complete chemoselectivity was observed for the oxidation of all functional sulfides. Sulfones were, however, the main products of the reaction when the complexes were not coated on silica gel. The influence of silica gel as the support of these reactions was also investigated and it was demonstrated that it alters the reactivity of the complex but it is not responsible for the excellent chemoselectivity of the complexes. The complex [MoO(O2)2(pyrazole) (H2O)] proved to be more reactive than [MoO(O2)2(Opyr) (H2O)].