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.