Kinetics and mechanism of the oxidation of hydroxylamine by aquavanadium(V) ions in aqueous perchlorate media

Abstract

This oxidation has been investigated in the acidity range 1–5 mol dm^–3 HClO₄ at a constant ionic strength of 5 mol dm^–3 over the temperature range 25–60 °C. The consumption ratio |Δ[V^V]| : |Δ[NH₂OH]| is found to lie between 1 : 1 and 2 : 1 using an excess of V^V. With an excess of NH₂OH, the reaction is first order in [V^V] and the order in [NH₂OH] is between zero and one. The variation of the pseudo-first-order rate constant with [NH₂OH] and [H⁺] shows that two pathways operate, one via the complex VO₂^+˙NH₃OH⁺_aq. and the other via V(OH)₂^3+˙ NH₃OH⁺. Values for the overall enthalpy and entropy of activation are determined for each pathway.