Copper and Cobalt Co-catalyzed Selective Electrooxidation of Phenol to p-Benzoquinone Under Mild Conditions

Abstract

Selective oxidation is still a challenge for targeted conversion of biomass derived substance to high-value added products. Herein we report an efficient electrochemical strategy to transform phenol into p-benzoquinone, by tandem oxidations of CuSO4 and CoSO4 catalysts in an electrolyte. Co3+ generated at the anode from oxidation of Co2+ diffuses to the solution and reacts with phenol to form hydroquinone, which is subsequently oxidized by Cu2+ in the solution selectively to p-benzoquinone. The active metal ions (Cu2+ and Co3+) are continuously regenerated at the anode through electrooxidation and the targeted p-benzoquinone is accumulated in the electrolyte solution. The Ultraviolet-visible spectra and electrochemical test results reveal that Cu2+ reacts with hydroquinone immediately, and p-benzoquinone remains stable in CuSO4 solution. By optimizing catalyst concentrations and reaction temperatures (0.2 M CuSO4, 0.005 M CoSO4 and 50 °C), the highest p-benzoquinone yield was improved to 47 %. The developed copper-cobalt co-catalyzed system provides a promising approach to selectively prepare high-value benzoquinone compounds under mild reaction conditions.