Simultaneous phenol oxygenation and quinone hydrogenation with water as both the oxygen and hydrogen source

Abstract

Oxygenation and hydrogenation in the production of bulk chemicals traditionally rely on molecular oxygen and hydrogen, respectively. Coupling these two reactions using water as both the oxygen and hydrogen source offers an attractive and sustainable approach for industrial processes, yet it faces significant challenges, particularly due to the high energy barrier associated with water splitting. The present study demonstrates that phenol oxygenation and benzoquinone hydrogenation can be effectively coupled through a bio-inspired mechanism involving a geminal diol adduct formed from water and benzoquinone, significantly facilitated by Brønsted acids. In this reaction, water serves as both the oxygen and hydrogen source, enabling the simultaneous production of two valuable feedstocks, 2,3,5-trimethylbenzoquinone and 1,4-hydroquinone. Detailed mechanistic insights were obtained through kinetic analysis, ¹⁸O-labeling experiments, and control experiments, all of which suggest that the critical redox step proceeds via hydroxyl cation transfer from the geminal diol intermediate to the phenol ring. This strategy may be feasible in other industrial reactions currently dependent on molecular oxygen and hydrogen, holding significant potential for energy savings.