Kinetics and mechanism of ruthenium(III)-catalysed oxidation of allyl alcohol by molecular oxygen

Abstract

Oxidation of allyl alcohol by molecular oxygen catalysed by ruthenium(III) chloride in the pH range 1.0-3.0 is reported. The kinetics of the reaction, in the pH range 1.0-2.0, indicate a first-order dependence on ruthenium(III) ion and allyl alcohol concentrations and a zero-order dependence with respect to molecular oxygen concentration. The rate of oxidation was also found to be directly proportional to the hydrogen ion concentration. In the pH range 2.0-3.0, the rate of oxidation of allyl alcohol was found to be first order with respect to ruthenium(III) ion, first order with respect to allyl alcohol, and inversely proportional to hydrogen ion concentration. The rate is one-half order with respect to the concentration of molecular oxygen. Mechanisms for the oxidation of allyl alcohol catalysed by ruthenium(III) have been proposed in the pH ranges 1.0-2.0 and 2.0-3.0, wherein the reactions were shown to proceed through an oxidase route and an atom transfer (oxygenase) route, respectively. Separation of the catalyst from the reaction products was achieved using an ultrafiltration membrane technique, where the membrane was used as a separating agent. The oxidation products were identified by means of electrochemical techniques.