Kinetics and mechanisms of oxidation of reversible organic systems with cobalt(III) in acidic perchlorate media

Abstract

The oxidation kinetics of some quinols with cobalt(III) perchlorate have been investigated at different temperatures and acidities by means of a stopped-flow technique. The rate law is of the form –½d [Co^III]/dt=(k_a+k_bK_h[H+]^–1)[ Co^III][Quinol]; the term k_a refers to Co³⁺(aq) and k_b to[Co(OH)]²⁺(aq) specjes. For Co³⁺(aq), comparison has been made with other systems in the light of the Marcus theory: a large number of reaction rates agree with an experimental correlation oftheformk =αZexp(–ΔG*/RT), where α= 10^–5–10^–6 and ΔG*=λ[1 +(δG^⊖/λ)²]/4, according to Marcus theory. However, the small range of values of the second-order rate constants for [CO(OH)]²⁺(aq) suggests a limiting behaviour for this species.