Kinetics and mechanism of Ru(III)-edta catalyzed oxidation of cis-cyclootene by molecular oxygen

Abstract

The homogeneous oxidation of cis-cyclooctene with molecular oxygen catalyzed by potassium chloro(ethylenediaminetetraacetato)ruthenium(III), K[Ru(H-EDTA)Cl]·2H₂O, was investigated in the temperature range 310-335 K,μ=0.1 M KC1 in 1:1 water-dioxane mixture. The rate of oxidation of cis-cyclooctene was found to be first order with respect to catalyst and cyclooctene concentrations, and one-half order in molecular oxygen concentration. Based on the kinetic data, a μ-peroxoruthenium(IV)cyclo-octene complex is suggested as an active intermediate for the formation of cyclooctene oxide as a major product. A small quantity of 2-cycloocten-1-ol was also obtained in the reaction. The formation of 2-cycloocten-1-ol may be explained on the basis of the formation of a peroxometallocycle involving the catalyst, cyclooctene and dioxygen, which gives rise to an ene insertion product. A free radical route for the formation of 2-cycloocten-1-ol can be ruled out on the basis of the absence of any hydroperoxide intermediate. The activation parameters for the oxidation step corresponding to the rate constant were also calculated. The high enthalpy of activation ΔH^‡ of 26.8 kcal mol⁻¹ supports the O-O bond cleavage in either mechanism. The products were analysed by GLC, IR and NMR spectroscopies and by derivatization of the products.