Kinetics and mechanism of the oxidation of hydrazine with the dichlorotriaquoruthenium(V)-oxo complex in aqueous solution

Abstract

The kinetics and mechanism of the oxidation of hydrazine by dichlorotriaquomono-oxoruthenium(V) [O=Ru^V(H₂O)₃Cl₂]⁺ (1) was studied spectrophotometrically as a function of complex and hydrazine concentrations at ionic strength (μ=0.1-0.3 M) of Na₂SO₄ at a constant pH of 1.85. The rate of the reaction was followed by monitoring the disappearance of the MLCT band of the oxo complex, 1, at 420 nm. The rate of oxidation of hydrazine by 1 is first order with respect to complex and hydrazine concentrations. The rate increases when the ionic strength of the medium is increased. The oxidation of hydrazine was studied at three different temperatures, and the activation parameters ΔH^≠ and ΔS^≠ were evaluated. A mechanism involving the formation of an active diazene (HN=NH) intermediate (in a rate-determining step) that rapidly undergoes two-electron oxidation to give N₂ is proposed for an overall four-electron oxidation of hydrazine.