Kinetics and mechanism of oxidation of aliphatic alcohols by oxone catalyzed by Keggin type 12-tungstocobaltate(II)

Abstract

The oxidation of various aliphatic alcohols by ox one catalyzed by Kegin type [Co^IIW₁₂O₄₀]^6- has been studied in a buffer medium of <i>p</i>H = 4. The reaction proceeds by the oxidation of [Co^IIW₁₂O₄₀]^6- to [Co^IIIW₁₂O₄₀]^5- by oxone which then oxidizes the alcohol in a rate &nbsp;determining step generating alcohol free radical. The reaction is accelerated by increase in the <i>p</i>H of the solution due to the protonation equilibria of the oxidant. The reaction between oxone and [Co^IIW₁₂O₄₀]^6- has also studied and is found to proceed in two one-electron steps, involving formation HSO₅^2- &nbsp;free radical in a slow first step followed by its reaction with reductant in a fast step. The reaction rate is inhibited by the [H⁺] due to protonation equili bria of HSO₅^-which is the active species. Decreasing the relative permittivity of the medium increases the rate of the reaction which is attributed to the formation of an outer-sphere complex between the reactants. The activation parameters determined for both the reactions support the proposed mechanisms.