Ascorbate-dependent mono- vs. dioxygenase mechanism for Ru(III)-EDTA catalyzed oxidation of adamantane by molecular oxygen

Abstract

Oxygen-atom transfer from molecular oxygen to adamantane in the presence and absence of ascorbic acid is catalyzed by R(III)-EDTA in a 1:3 (v/v) mixture of water and 1,4 dioxane. The kinetics and mechanisms of these reactions were investigated at 35°C, μ=0.1 M KNO₃ in the range pH 1.75-2.75. The rate of oxidation of adamantane is first order with respect to the concentrations of Ru(III)-EDTA complex, ascorbic acid and molecular oxygen, fractional order with respect to adamantane concentration and inverse first order with respect to hydrogen-ion concentration. In the absence of ascorbic acid the observed reaction orders with respect to the concentrations of adamantane, dioxygen and hydrogen ion were, one, one half and zero, respectively. The rates of formation of products (alcohols and ketone) were found to depend on the presence of ascorbic acid. A comparative study of the oxidation of adamantane from the viewpoints of product analysis, kinetics and mechanism is reported, and the oxidation reactions are shown to proceed through dioxygenase and monooxygenase routes in the absence and presence of ascorbic acid, respectively.