Kinetics and mechanism of O–O bond cleavage in the reaction of [RuIII(edta)(H2O)]− with hydroperoxides in aqueous solution

Abstract

The reactions of [Ru^III(edta)(H₂O)]⁻ (1) (edta = ethylenediaminetetraacetate) with tert-butylhydroperoxide (^tBuOOH) and potassium hydrogenpersulfate (KHSO₅) were studied kinetically as a function of oxidant concentration and temperature (10–30 °C) at a fixed pH of 6.1 using stopped-flow techniques. Kinetic results were analyzed by using global kinetic analysis techniques. The reaction was found to consist of two steps involving the rapid formation of a [Ru^III(edta)(OOR)]²⁻ intermediate, which subsequently undergoes heterolytic cleavage to form [(edta)Ru^VO]⁻. Since [(edta)Ru^VO]⁻ was produced almost quantitatively in the reaction of 1 with the hydroperoxides ^tBuOOH and KHSO₅, the common mechanism is one of heterolytic scission of the O–O bond. The water soluble and easy to oxidize substrate 2,2′-azobis(3-ethylbenzithiazoline-6-sulfonate (ABTS), was employed to substantiate the mechanistic proposal. Reactions were carried out under pseudo-first order conditions for [ABTS] ≫ [hydroperoxide] ≫ [1], and were monitored as a function of time for the formation of the one-electron oxidation product ABTS˙⁺. The detailed suggested mechanism is consistent with the reported rate and activation parameters, and discussed in reference to the results reported for the reaction of [Ru^II(edta)(H₂O)]⁻ with H₂O₂.