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

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-gC(3)N(4)-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.