Heterocyclic amine salts of Keggin heteropolyacids used as catalyst for the selective oxidation of sulfides to sulfoxides

A range of sulfides can be selectively oxidized to the corresponding sulfoxides in good yields using catalytic quantities of heterocyclic amine salts (quinoline, cinchonine, and cinchonidine) of Keggin heteropolyacids with different green oxidants. The cinchonine heteropolyacid catalyst is easily recoverable and reusable without loss of its catalytic activity, and an enantiomeric excess can be obtained.