Bromate ion oxidation of cobalt(III) complex of ethylenediamine-N,N,N',N'- tetraacetic acid in aqueous acidic medium: Existence of an autocatalytic process

Abstract

spectrophotometry, occurs in two stages: an initial phase followed by an autocatalytic step, the reaction is autocatalytic because bromine, a product of the initial reaction, catalyses the reaction by combining with [Co(edta)]^2-. The breakdown product of bromine is bromide which further reacts with excess bromate ion complimenting to this autocatalysis. The rate expression for the initial phase is: -<em>d</em>[Co(edta)^2-]/<em>dt </em>= 6<em>k</em>[Co(edta)^2-][BrO] at a constant [H⁺]. At [H⁺] = 0.02 mol dm^-3, <em>k </em>= (2.29±0.05) x 10^-⁴ dm^-³ mol^-1 S^-1. The dependence of <em>k </em>on [H⁺] in the region 0.002-0.02 mol dm^-3 follows the equation <em>k= </em>k₀ + <em>k, </em>[H⁺]<em>. </em>The value of <em>k</em>₀ = (1.92 ± 0.05) x 10^-5 dm³ mol^-1 s^-1 and that of <em>k</em>₁ = (5.38±0.10) x 10^-1 dm⁹mol^-3 s^-1. A plausible mechanism has been suggested involving outersphere pathways.