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 [Os_VIII]= 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][Os^VIII][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.