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.