A ruthenium(III) analogue of the model peroxidase system: Ru(III)-EDTA-ascorbate-H₂O₂ in the catalytic epoxidation of unsaturated hydrocarbons

Abstract

The epoxidation of cis-cyclooctene, styrene and trans-stilbene to the corresponding epoxides by a RU(III) analogue of the model peroxidase system, involving Ru(III)-EDTA-ascorbic acid and hydrogen peroxide, was investigated at 30°C and μ=0.1 M KNO₃ in a 1:2 (v/v) mixture of water and 1,4-dioxane in acidic medium. The kinetic parameters of the complicated oxidation reactions were determined as a function of substrates, catalyst, ascorbic acid, hydrogen peroxide and hydrogen ion concentrations, in order to determine the reaction order with respect to each of these reactants and to establish the mechanism. The rate of the epoxidation is first order with respect to the concentration of the substrates, catalyst, ascorbic acid and hydrogen peroxide and inverse first order with respect to the hydrogen ion concentration. On the basis of kinetics and experimental results, the rate laws for the epoxidation reactions were derived and their mechanisms discussed. The order of the reactivity of the substrates observed is cis-cyclooctene > styrene > trans-stilbene, as was found with other closely related systems.