One‐Step Approach to 2,5‐Diformylfuran from Fructose by Proton‐ and Vanadium‐Containing Graphitic Carbon Nitride

Abstract 5‐Hydroxymethylfurfural (HMF) was selectively synthesized from fructose by using protonated graphitic carbon nitride [g‐C3N4(H+)] as a solid acid. With g‐C3N4 as the same precursor material, 2,5‐diformylfuran (DFF) was efficiently obtained from aerobic oxidation of HMF by using vanadium‐doped g‐C3N4 (V–g‐C3N4) as an environmentally benign heterogeneous catalyst with atmospheric pressure of molecular oxygen as the oxidant. In addition, a combination of g‐C3N4(H+) and V–g‐C3N4 successfully afforded the direct synthesis of DFF from fructose through g‐C3N4(H+)‐promoted fructose dehydration and V–g‐C3N4‐catalyzed successively aerobic oxidation of HMF to DFF in a one‐pot and two‐step process. Moreover, a bifunctional catalyst made of protonated V–g‐C3N4 [V–g‐C3N4(H+)] allowed one‐pot as well as one‐step direct transformation of fructose into DFF. Under optimized conditions, 80 % yield of HMF and 82 % yield of DFF were obtained from g‐C3N4(H+)‐promoted fructose dehydration and V–g‐C3N4‐catalyzed HMF oxidation, respectively. Stepwise addition of g‐C3N4(H+) and V–g‐C3N4 in the one‐pot process improved the DFF yield up to 63 % from fructose. In contrast, V–g‐C3N4(H+)‐catalyzed direct one‐step transformation of fructose into DFF led to a DFF yield of 45 %. The research highlights a one‐step approach to DFF from fructose with functional g‐C3N4 catalyst.