One-Step Approach to 2,5-Diformylfuran from Fructose by Using a Bifunctional and Recyclable Acidic Polyoxometalate Catalyst

A series of acidic cesium salts of molybdovanadophosphoric heteropolyacids (CsMVP-HPAs) are developed as bifunctional and recyclable catalysts for a one-step approach to 2,5-diformylfuran (DFF) from fructose with molecular oxygen as the oxidant under environmentally benign conditions. The CsMVP-HPAs afford the direct synthesis of DFF from fructose through acidic site (H)-promoted fructose dehydration and metallic site (V)-catalyzed successive aerobic oxidation of 5-hydroxymethylfurfural (HMF). The catalytic performances of CsMVP-HPA toward fructose dehydration and HMF oxidation are related to its acid density and V content, respectively. Moreover, the increase in the V content of CsMVP-HPA results in its decreased acid density, which suggests its converse catalytic performance toward fructose dehydration and HMF oxidation. An optimum balance between the dehydration and oxidation functions of CsMVP-HPAs reveals that a ratio of acid density to molar concentration of V between 1.64 and 3.34 achieves a maximum yield of 60% for DFF from fructose with Cs3HPMo11VO40 as a catalyst under atmospheric pressure of oxygen. Moreover, Cs3HPMo11VO40 behaves as a heterogeneous catalyst and can be easily reused at least for four times. This research highlights an efficient bifunctional catalyst for transforming renewables into fine chemicals in tandem reactions of dehydration and oxidation.