Theoretical study on molecular mechanism of aerobic oxidation of 5-hydroxymethylfurfural to 2,5-diformyfuran catalyzed by VO2+ with counterpart anion in N,N-dimethylacetamide solution†
a
Jin-Shan
Xiong,
a
Ting
Qi,
a
Hong-Mei
Yang,
a
Han-Yun
Min,
a
Hua-Qing
Yang
*a
and
Chang-Wei
Hu
b
Abstract
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 VO2+ with counterpart anion in N,N-dimethylacetamide (DMA) solution have been theoretically investigated. In DMA solution, the stable VO2+-containing complex is the four-coordinated [V(O)2(DMA)2]+ species. For the gross reaction of 2HMF + O2 → 2DFF + 2H2O, 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 –CH2 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.
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