Cobalt(II) mediated electro-oxidation of toluene and its derivatives

The oxidation of toluene and its derivatives is crucial for the chemical industry. Traditional liquid-phase oxidation technologies require high-temperature and high-pressure conditions, which causes high safety risks and urgently requires alternatives. This article reports an electrochemical oxidation method using cobalt acetate as a mediator, which successfully realizes the mild oxidation of toluene. The method turns toluene into highly active radicals by the electrochemically generated Co(III) from cobalt acetate, which significantly reduces the anodic potential in contrast to the direct electro-oxidation and the other reported mediated oxidation processes. The target products, benzaldehyde and benzoic acid, exhibit high yields at 85 °C as the ratio of AcO- to Co(II) is close to 2 in the homogeneous anhydrous electrolyte. A benzyl radical-centered mechanism for the Co(II) mediated electro-oxidation of toluene is proposed based on the cyclic voltammetry tests and a radical inhibiting experiment. The method has also been successfully applied to the derivatives of toluene.