Stoicheiometry and kinetics of the oxidation of hydroxylamine by peroxomonophosphoric acid in acidic perchlorate solutions and catalysis by iron(III) and iodide or iodine

Abstract

The stoicheiometry of the reaction of H₃PO₅ and NH₃OH⁺ is variable depending on the ratio of the reactants, and the products of oxidation are H₂N₂O₂, HNO₂, and HNO₃. When [NH₃OH⁺] > 10[H₃PO₅], the stoicheiometry was as in equation (i) and the kinetics were followed under this condition. The rate H₃PO₅+ NH₃OH⁺→ H₃PO₄+½H₂N₂O₂+ H₃O⁺(i) law is as in equation (ii) with k₁=(1.15 ± 0.10)× 10^–3 dm³ mol^–1 s^–1 at 45 °C. The reaction is independent –d[H₃PO₅]/dt=k₁[H₃PO₅][NH₃OH⁺](ii) of [H⁺] in the range 0.1–2.0 mol dm^–3, but is catalysed by Fe^II or Fe^III, and iodide or iodine. The rate laws in the last two cases are as in equations (iii) and (iv) where [I] represents the concentration of –d[H₃PO₅]/dt=[H₃PO₅][NH₃OH⁺](k₁+k₂[Fe^III])(iii), –d[H₃PO₅]/dt=[H₃PO₅](k₁[NH₃OH⁺]+k₃[I]+k₄[I][NH₃OH⁺])(iv) iodide, iodate, or iodine. The values of k₂, k₃, and k₄ were found to be 1.5 × 10² dm³ mol^–1 s^–1, 1.45 × 10³ dm³ mol^–1 s^–1, and 1.64 × 104 dm⁶ mol^–2 s^–1 at 45 °C.