Selective Synthesis of 2,5-Diformylfuran and 2,5-Furandicarboxylic Acid from 5-Hydroxymethylfurfural and Fructose Catalyzed by Magnetically Separable Catalysts

Selective synthesis of various versatile compounds from biomass is of great importance to replace traditional fossil fuel resources. A novel magnetic catalyst, ZnFe1.65Ru0.35O4, was prepared via a simple alkali-coprecipitation method. The structure of the as-prepared catalyst was characterized, and its catalytic performance was investigated for aerobic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF) and 2,5-furatidicarboxylic acid (FDCA) under different reaction conditions. A high DFF yield of 93.5% was obtained for the reaction at 110 degrees C for 4 h in dry DMSO, whereas the maximum FDCA yield of 91.2% was achieved for the reaction at 130 degrees C for 1:6 h in H2O/DMSO (1:2, v/v). More importantly, a plausible reaction pathway was proposed for the aerobic oxidation of HMF into FDCA, with the rate-determining step determined through kinetic study. In addition, DFF or FDCA could be produced from fructose by sequentially using a magnetic solid acid (Fe3O4-RGO-SO3H) and ZnFe1.65Ru0.35O4. The dehydration of fructose in the presence of Fe3O4-RGO-SO3H resulted in HMF. After the removal of Fe3O4-RGO-SO3H from the reaction solution with a magnet, HMF was further oxidized in the catalysis of ZnFe1.65Ru0.35O4. These two consecutive steps gave DFF in 73.3% yield and FDCA in 70.5% yield, under the respective optimum reaction conditions. The direct synthesis of DFF or FDCA from fructose avoids tedious separation of intermediate HMF, leading to savings, with regarii to both time and cost.