Sulfide oxidation catalyzed vanadyl complexes of N-salicylidene α-amino acids at low catalyst loading

Sulfoxides are extensively used in chemical and pharmaceutical industries. Various catalytically synthetic methods were reported, but in common 1–10 (mol)% catalyst loading were demanded. Sulfide oxidation catalyzed by vanadyl complexes of N-salicylidene α-amino acids with catalyst loading as low as 0.03 (mol)% gave high yields at room temperature with aqueous hydrogen peroxide as an oxidant, which is a green, solvent-free, energy-saving and easy-operated protocol. In contrast, vanadyl complexes of N-salicylidene amino alcohols could not, even at 0.1 (mol)%. The possible reason is that the stronger acidity of N-salicylidene α-amino acids makes their vanadyl complexes stable to aqueous hydrogen peroxide. This rule may be used in designing other high efficient catalysts, especially with aqueous hydrogen peroxide as an oxidant.