An Effective Catalytic Epoxidation of Terpenes with Hydrogen Peroxide ­under Organic Solvent-Free Conditions

A catalytic system that operates well for the epoxidation of α-pinene, a very challenging substrate, at near-neutral pH and ambient temperature without organic solvent was developed. With hydrogen peroxide as a terminal oxidant, combination of Na2WO4, PhP(O)(OH)2, and [Me(n-C8H17)3N]HSO4 successfully catalyzed the epoxidation of α-pinene to give α-pinene oxide in 95% selectivity at 91% conversion, while the previously published conditions that use NH2CH2P(O)(OH)2 as a promoter provide no epoxide. The method is also well applicable to the epoxidation of the other acid-sensitive terpenes.