Catalytic epoxidation of olefins by an effective monooxygenase system: Ru(III)-EDTA-ascorbate-O₂

Abstract

The Ru(III)-EDTA-ascorbate-molecular oxygen system was found to be an efficient catalyst for the epoxidation of olefins in mixed aqueous acidic solvent, water:dioxane (1:2) (v/v). Detailed kinetic, catalytic and equilibrium studies of the epoxidation of cis-cyclooctene, styrene and trans-stilbene with molecular oxygen catalyzed by Ru(III)-EDTA-ascorbate complex are reported at 30°C and μ=0.1 M KNO₃. The Kinetic parameters of the complicated epoxidation reactions were found to follow first-order kinetics with respect to substrate, ascorbic acid, catalyst and molecular oxygen concentrations. An inverse first-order dependence in hydrogen ion concentration was observed for all the epoxidation reactions studied. A monooxygenase model mechanism is proposed for the epoxidation reaction, in which the transfer of one of the oxygen atoms to olefin and the reduction of the other oxygen atom to water take place by heterolytic cleavage of the O---O bond. The reactivity of the olefins was observed to decrease in the order: cis-cyclooctene > styrene > trans-stilbene.