Epoxidation of cyclohexene with active oxygen species produced by reducing dioxygen in the presence of Br– ion

Abstract

Oxidation of cyclohexene to cyclohexene oxide, cyclohex-2-en-1-one, and cyclohex-2-en-1-ol proceeded by adding Br^– ions to an air-equilibrated acetonitrile suspension containing cyclohexene as a substrate, hexylviologen as an electron mediator, benzoic anhydride as an activating reagent, and insoluble zinc powder as a reductant. With increasing concentration of Br^– ions, the epoxidation selectivity increased up to 85% with about 60% Zn-utilizing efficiency. The oxidation mechanism was discussed in relation to the redox properties of the chemical species contained in this catalytic system. The active oxygen species for producing cyclohex-2-en-1-one and cyclohex-2-en-1-ol, and that for producing cyclohexene oxide may be hypobromous radical (BrO˙) and hypobromous anion (BrO^–), respectively.