Reaction of [RuIII(edta)(H2O)]− with H2O2 in aqueous solution. Kinetic and mechanistic investigation

Abstract

The reaction of [Ru^III(edta)(H₂O)]⁻ (1) (edta = ethylenediaminetetraacetate) with hydrogen peroxide was studied kinetically as a function of [H₂O₂], temperature (5–35 °C) and pressure (1–1300 atm) at a fixed pH of 5.1 using stopped-flow techniques. The reaction was found to consist of two steps involving the rapid formation of a [Ru^III(edta)(OOH)]²⁻ intermediate which subsequently undergoes parallel heterolytic and homolytic cleavage to produce [(edta)Ru^VO]⁻ (45%) and [(edta)Ru^IV(OH)]⁻ (55%), respectively. The water soluble trap, 2,2′-azobis(3-ethylbenzithiazoline-6-sulfonate) (ABTS), was employed to substantiate the mechanistic proposal. Reactions were carried out under pseudo-first conditions for [ABTS] ≫ [HOBr] ≫ [1], and were monitored as a function of time for the formation of the one-electron oxidation product ABTS˙⁺. A detailed mechanism in agreement with the rate and activation parameters is presented, and the results are discussed with reference to data reported for the corresponding [Fe^III(edta)(H₂O)]⁻/H₂O₂ system.