Biomimetic Aerobic Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid in Deep Eutectic Solvents through the Efficient Electron Transfer.

Selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) has long been a formidable challenge under mild conditions. Deep eutectic solvents (DESs) have shown remarkable efficiency in the oxidation of HMF as a sustainable solvent. These solvents not only enhance solubilization but also activate biomass-derived hydroxyl compounds via hydrogen bonds reconstruction. This study leverages the architecture and functionality of natural enzymes and coenzymes in the respiratory chain system to develop a unique biomimetic catalytic system. In this system, HMF is oxidized to FDCA in imidazole-based DESs with polyoxometalates as catalyst and para-benzoquinone as electron transfer mediators. The findings demonstrate that the adjustment of hydrogen bond acceptor (HBA) or hydrogen bond donor (HBD) enables precise control over the hydrogen bond strength in DESs, thereby accurately regulating the distribution of HMF oxidation products. Furthermore, the optimization of hydrogen bond strength can also activate the OH bond in HMF, consequently expediting the oxidation reaction. The cyclic voltammetry measurements provide compelling evidence of dioxygen activation and efficient electron transferring in a biomimetic catalytic system, resulting in a remarkable 21-fold increase in current density. This research not only advances utilization and development of biomass resources but also offers novel perspectives into constructing efficient catalytic oxidation systems.