A novel wacker route based on ruthenium(III) ion for olefin oxidation to ketones

Abstract

The oxidation of 1-hexene to the end ketone 2-hexanone by molecular oxygen is catalysed by Ru(III) ion, [RuCl₂(H₂O)₄]⁺ at 35°C (μ=0.1 M) in 1:1 (v/v) water-dioxane solution at pH 2.00. The reaction shows a firstorder dependence in catalyst and substrate concentrations and a one-halforder dependence with respect to molecular oxygen concentration. The product of oxidation, 2-hexanone, as identified and analysed by GLC, is formed in 54% yield. A mechanism involving a combination of a peroxometallocycle and the Wacker oxidation route to ketone formation is proposed. Finally, on the basis of kinetics and the mechanism proposed, a rate law for the oxidation reaction was derived and the corresponding rate constants evaluated. The various equilibrium constants involved in the mechanism have been directly obtained by spectrophotometric measurements. The system represents the first simple monometallic and noncorrosive pathway for Wacker oxidation of olefins to ketones, and proceeds with a turnover frequency of 62 mol ketone per mol catalyst per hour at 35°C.