The Accelerated NHPI-PINO Cycling Mediated by Surface Co-Superoxo for Efficient Aerobic Oxidation of Alcohols to Acids

Oxidation of alcohols to acids is a key transformation in the chemical industry; however, one-pot oxidation to acids via the environment-friendly and cost-effective method remains challenging. In this study, a series of ZIF-67-derived CoO x catalysts were synthesized, and ZIF-CoO x -2 exhibits a high conversion of 95.2% 2-methyl-1-butanol and selectivity of 99% toward 2-methyl-1-butanic acid by O 2 in the presence of NHPI. In addition, this protocol is also efficient in the one-pot oxidation of a variety of alcohols to acids. The gram-scaled reaction can also be conducted using O 2 or even air as the oxidant. EPR analysis indicates that the NHPI-PINO cycle plays an important role in this process. Quenching experiments and Raman analysis indicate that Co-superoxo on the surface of ZIF-CoO x -2 is an important oxidizing species facilitating the NHPI-PINO cycle. DFT calculations further reveal that the NHPI-PINO cycle facilitates H-abstraction from alcohols by PINO, as well as H-abstraction from NHPI by ROO•, thus apparently enhancing the conversion and selectivity. This study offers a sustainable method to directly oxidize alcohols to acids with high conversion and selectivity, enriching our understanding on the importance of synergistic interactions between the surface superoxo species and the NHPI-PINO cycle in the selective oxidation of organic substrates. Graphical Co-superoxo (≡Co—OO•) species on the surface of the recyclable ZIF-CoO x -2 catalyst facilitate the NHPI-PINO cycle, efficiently promoting the selective aerobic oxidation of alcohols to carboxylic acids via hydrogen abstraction. This catalytic system delivers up to 98% conversion and 99% selectivity with broad substrate scope and gram-scale applicability.