Kinetics and mechanism of the oxidation of iodide by trans-dioxoruthenium (VI)

Abstract

The kinetics of reduction of trans-[Ru(tmc)O2]2+(tmc = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) by iodide has been studied in aqueous acidic solution. The reaction has the following stoichiometry; trans-[RuVI(tmc)O2]2++ 3I–+ 2H+→trans-[RuIV(tmc)O(OH2)]2++ I3–. The rate law is –d[RuVI]/dt=(ka+kb[H+])[RuVI][I–] with ka= 0.041 ± 0.013 dm3 mol –1 s–1 and kb= 18.5 ± 0.2 dm6 mol –2 s–2 at 25.0 °C and 0.1 mol dm–3 ionic strength. For kaΔH‡= 42.9 ± 9.4 kJ mol–1 and ΔS‡=–131 ± 40 J K–1 mol–1, while for kb, ΔH‡= 36.9 ± 2.9 kJ mol–1 and ΔS‡=–97 ± 10 J K–1 mol–1. A mechanism involving oxygen-atom transfer from RuVI to iodide is consistent with the data.