Kinetics and mechanism of the osmium(VIII)-catalyzed oxidation of phosphite by hexacyanoferrate(III) ion in aqueous alkaline media

The oxidation of phosphite by alkaline [Fe(CN)6]3– occurs with a measurable rate at 35 °C in the presence of OsVIII according to equation (i) and rate law (ii), where k is the rate constant and K3 is the equilibrium constant for 2[Fe(CN)6]3–+[HPO3]2–+ 2[OH]–→ 2[Fe(CN)6]4–+[HPO4]2–+ H2O (i), –d[Fe(CN)63–]/dt=2kK3[OsVIII][OH–][HPO32–]//1 +K3[OH–](ii) the complex formation between OsVIII and [OH]–; k and K3 are 1.0 ± 0.05 dm6 mol–2s–1 and 32 ± 3 dm3 mol–1 respectively at 35 °C and I= 1.0 mol dm–3. A spectrophotometric value of K3 is 30 ± 6 dm3 mol–1. A mechanism consistent with the above facts has been suggested.