Copper-Catalyzed Oxidation of 5-Hydroxymethylfurfural to 2,5-Diformylfuran Assisted by TEMPOL in Liquid Sunlight Methanol.

2,5-diformylfuran (DFF) is a significant biomass-derived compound with diverse applications in novel furan-based materials, fragrances, fuel additives, and drug synthesis. A pivotal challenge in DFF synthesis was developing a method to produce DFF under mild conditions using sustainable feedstocks. In this study, an affordable 4-hydroxy-2,2,6,6-tetramethylpiperidine (TEMPOL)- assisted Cu(OAc)₂ catalytic system for aerobic oxidation reaction of HMF to DFF in liquid sunlight methanol solvent was developed. The effects of parameters such as metal species, catalyst amount, solvent species, base structure, and reaction temperature were systematically investigated. The evolution of product distribution in the reaction solution at various times was monitored and analyzed using 1H-NMR spectroscopy. FT-IR and ESI-MS characterizations were employed to integrate experimental findings and elucidate the reaction mechanism. The highest DFF yield of 96 % and complete conversion of HMF were obtained. Furthermore, a total DFF yield of 68.6 % was achieved from fructose using a two-steps method, demonstrating the potential for scalable production. The establishment of this catalytic system presents a novel approach for the selective preparation of DFF from sustainable feedstock.