Kinetics and mechanism of I(+ 3) reactions and consequences for other iodine reactions

Abstract

This article presents new kinetic studies of the disproportionation of I(+ 3) and of its oxidation by H₂O₂. It also provides an update of the previously proposed model for reactions of iodine compounds with oxidation numbers from − 1 to + 5 with each other and with H₂O₂. This model explains the kinetics of several reactions, including the oxidation of iodine by H₂O₂. We show that the reduction of HOI by H₂O₂ results from ${\text{HOI }} + {\text{ H}}_{{2}} {\text{O}}_{{2}} \to {\text{HOOI }} + {\text{ H}}_{{2}} {\text{O}}$ followed by the reversible reaction ${\text{HOOI}} \rightleftharpoons {\text{I}}^{ - } + {\text{ H}}^{ + } + {\text{ O}}_{{2}}$. An analysis of previous measurements of the kinetic constant k(HOI + H₂O₂) explains the large differences between the values proposed in the literature and gives k(HOI + H₂O₂) = 6 M⁻¹ s⁻¹. The reversibility of the reaction ${\text{HOOI}} \rightleftharpoons {\text{I}}^{ - } + {\text{ H}}^{ + } + {\text{ O}}_{{2}}$ suggests a new explanation for the effect of oxygen on the Bray–Liebhafsky reaction. H₂O₂ would oxidize HOOI by a radical mechanism.