Kinetics and mechanism of the oxidation of phosphite with chloramine T catalyzed by osmium(VIII) in alkaline solutions

Abstract

The osmium(VIII)-catalyzed oxidation of phosphite by chloramine T was studied by determining chloramine T (cat) iodometrically. The rate law (i) holds for [OH^–]= 0.05–0.5 mol dm^–3 and [HPO₃^2–]= 0.005–0.05 mol dm^3–, where K₁ is defined by equation (ii); K₂ and K₃ are the –d[cat]/dt=k₁k₂[cat][Os^VIII][HPO₃^2–]//_{1 +K1[OH^–]+K2[HPO3^2–]+K1K3[HPO3^2–][OH^–]}(i), [OsO₄(OH)₂]^2–+ OH^– [graphic omitted] [OsO₅(OH)]^3–+ H₂O (ii) equilibrium constants of formation of complexes between [OsO₄(OH)₂]^2– and HPO₃^2– and [OsO₅(OH)]^3– and HPO₃^2– respectively. The former complex reacts with cat. The values of k₁, K₁, K₂, and K₃ were found to be 4.0 dm³ mol^–1 s^–1, 5 dm³ mol^–1, 300 dm³ mol^–1, and 60 dm³ mol^–1 respectively at 70 °C.