Physically hybrid Zr(OH)4 + CuO catalyzed selective aniline oxidation: A new Ph- N ˙ OH mediated mechanism

Abstract

Developing the sustainable and cost-effective heterogeneous catalytic system for controlling chemoselectivity holds substantial importance in fine organic chemicals. Herein we construct a unique Zr(OH)₄ + CuO physically hybrid system for selective oxidation of anilines. Zr(OH)₄ alone leads to azoxybenzene formation, and Zr(OH)₄ + CuO shifts the reaction favorably toward nitrosobenzene. The proximity study indicates Zr(OH)₄ + CuO outperforms its counterparts synthesized through methods like ball-milling, loading, and coprecipitation, because the closer proximity exhibits stronger chemical interaction, restricting the activity of Zr-OH hydroxyl sites. Through mechanistic experiments, in situ DRIFT-IR and DFT calculations, a new Ph-$\dot{N}$OH intermediate mechanism is firstly proposed. Two Ph-$\dot{N}$OH self-condensate to form azoxybenzene for only Zr(OH)₄, whereas Zr(OH)₄ + CuO could promote rapid transformation of Ph-$\dot{N}$OH to nitrosobenzene on CuO through a hydrogen transfer process. Moreover, Zr(OH)₄ + CuO displays good recyclability and robust scalability. This is the first report demonstrating the utilization of a physically hybrid catalyst to adjust the selectivity of the aniline oxidation reaction.