Selective Oxidation of Organic Sulfides to Sulfoxides by Hydrogen Peroxide with Trirutile-Type Solid Oxide Catalyst HNbMoO6

Abstract

Selective oxidation of organic sulfides to sulfoxides has been the subject of extensive research because of their importance of sulfoxides as intermediates in various organic reactions. One of the simplest methods for oxidation of sulfides to sulfoxides is the use of hydrogen peroxide as an oxidant in the presence of a catalyst. Though a number of catalysts including soluble metal complexes have been used for the reaction, there are a few reports employing a heterogeneous catalyst despite the advantage in separation and reuse of the catalyst. In this paper, we introduce a new heterogeneous catalyst, HNbMoO6, which shows an excellent catalytic activity in the oxidation of sulfides. Trirutile-type solid oxide, AMM’O6, was first synthesized in 1970. Since then, many applications of the solid oxide in various fields such as non-linear optics and composites have been reported. However, the catalytic activity of the oxide in organic reactions has not been well studied in spite of the potentials expected from the two different transition metals contained in the solid oxide. Recently, we reported a selective sulfoxidation of allylic sulfides catalyzed by the trirutile-type solid oxide, LiNbMoO6 and successfully applied the oxidation method to the synthesis of Lansoprazole. Because of the good catalytic activity shown by the LiNbMoO6 in the sulfoxidation of sulfides, we decided to test other trirutile-type solid oxides, AMM’O6 (A=H, Li, M=Nb, Ta, M’=Mo, W), as a catalyst in the hydrogen peroxide oxidation of sulfides to sulfoxides (Eq. 1).