Stoichiometry, kinetics and mechanism of the oxidation of hydroxyammonium ion with iron(III) in acetate buffers
Abstract
Iron(III) reacts with hydroxyammonium ion in acetate buffers and in diffuse light according to equation (i), where FeIII represents the predominant form [Fe3O(O2CMe)6]+ and the rate law at FeIII+ NH3OH+→ FeII+½N2+ H2O + 2H+(i), 35 °C is (ii); k1 and k1k3/k2 were found to be (4.6 ± 0.2)× 10–2 dm3 mol–1 s–1 and 0.31 ± 0.01 dm3–d[FeIII]/dt=k1k3[FeIII][NH3OH+][H+]/(k2[FeII]+k3[H+])(ii), mol–1 s–1 respectively at 35°C. The Ea for the k1 step is 103 kJ mol–1, but k1k3/k2 varies little with temperature. The rate law has been verified by reducing it to simpler forms by working at different concentrations of FeII and H+, at 60°C, and 6°C, in the presence of methyl methacrylate. At 60°C k2k3 and at 6 °C k2k3. The dark reaction stoichiometry is not fixed and the gaseous products are N2 and N2O.