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 [HPO32–]= 0.005–0.05 mol dm3–, where K1 is defined by equation (ii); K2 and K3 are the –d[cat]/dt=k1k2[cat][OsVIII][HPO32–]//1 +K1[OH–]+K2[HPO32–]+K1K3[HPO32–][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 HPO32– and [OsO5(OH)]3– and HPO32– 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.