Further revealing reaction mechanism on the oxidative behavior of 5-hydroxymethylfurfural

Solar energy-driven biomass refinery to produce high value-added chemicals is attracting more and more attention. However, precisely modulating for selective oxidation of biomass-derived platform chemical is still challenging. Further mechanism study on this oxidation process is highly desirable. In this work, theoretical study on the oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) at the atomic and molecular level is completed by density functional theory, oxidative reaction mechanism is further revealed. The two oxidation reaction pathways were identified, one is the hydroxymethyl group of HMF is oxidized to obtain 2,5-diformylfuran (DFF) and continue oxidized to form 5-formyl-2-furancarboxylic acid (FFCA) and finally FFCA is oxidized to obtain FDCA, the other is the aldehyde group of HMF is oxidized to form 5-hydroxymethyl-2-furancarboxylic acid (HMFCA), and then oxidized to form FFCA and FDCA. The potential energy surface information of the 24 possible reaction channels at the B3LYP/6-311 + G(d,p) level was obtained, including geometry structure optimization and frequency calculation of the stationary point. Results showed that hydroxymethyl group is easier to be oxidized to form DFF with the lower reaction energy barrier, this is consisted with most of the experimental results. Compared with O-2, the H-abstract reaction initiated by peroxy radicals of aldehyde or hydroxymethyl group is kinetically favorable. The new findings of two oxidation reaction processes of HMF (alcohol oxidation and aldehyde oxidation) in detail are of great significance for further utilizing and development of HMF.