Theoretical study on molecular mechanism of aerobic oxidation of 5-hydroxymethylfurfural to 2,5-diformyfuran catalyzed by VO(2)(+) with counterpart anion in N,N-dimethylacetamide solution

Vanadium-containing catalysts exhibit good catalytic activity toward the aerobic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformyfuran (DFF). The aerobic oxidation mechanism of HMF to DFF catalyzed by VO(2)(+) with counterpart anion in N,N-dimethylacetamide (DMA) solution have been theoretically investigated. In DMA solution, the stable VO(2)(+)-containing complex is the four-coordinated [V(O)(2)(DMA)(2)](+) species. For the gross reaction of 2HMF + O(2) → 2DFF + 2H(2)O, there are three main reaction stages, i.e., the oxidation of the first HMF to DFF with the reduction of [V(O)(2)(DMA)(2)](+) to [V(OH)(2)(DMA)](+), the aerobic oxidation of [V(OH)(2)(DMA)](+) to the peroxide [V(O)(3)(DMA)](+), and the oxidation of the second HMF to DFF with the reduction of [V(O)(3)(DMA)](+) to [V(O)(2)(DMA)(2)](+). The rate-determining reaction step is associated with the C–H bond cleavage of –CH(2) group of the first HMF molecule. The peroxide [V(O)(3)(DMA)](+) species exhibits better oxidative activity than the initial [V(O)(2)(DMA)(2)](+) species, which originates from its narrower HOMO–LUMO gap. The counteranion Cl(−) exerts promotive effect on the aerobic oxidation of HMF to DFF catalyzed by [V(O)(2)(DMA)(2)](+) species.