Kinetics and mechanism of the oxidation of hypophosphite with N-chlorotoluene-p-sulphonamide (chloramine T) catalysed by osmium (VIII) in alkaline solution

Abstract

The kinetics of osmium(VIII)-catalysed oxidation of hypophosphite, H2PO2–, with chloramine T (cat, N-chlorotoluene-p-sulphamide) was studied by estimating the latter iodometrically. The rate law (i) holds for [OH–]= 0.02–0.142, [H2PO2–]= 0.001–0.002, and [OsVIII]= 1 × 10–5 to 1 × 10–4 mol dm–3 where k1 is defined by equation (ii), k2 and k3 are the equilibrium formation constants ≳d[cat]//dt=k1k2[cat][OsVIII][H2PO2–]//1 +k1[OH–]+k2[H2PO2–]+k1k3[OH–][H2PO2–](i), [OsO3(OH)3]–+ OH– [graphic omitted], [OsO4(OH)2]2–+ H2O (ii) of complexes [OsO3(OH)3(H2PO2)]2– and [OsO4(OH)2(H2PO2)]3– respectively and the former reacts with chloramine T. The values of k1, k1, k2 and k3 were calculated to be 16.6 ± 0.5 dm3 mol–1 s–1, 37.6 ± 2, 175 ± 6.0 and 130 ± 5.0 dm3 mol–1 at 45 °C and I= 1.0 mol dm–3 respectively.