Further revealing reaction mechanism on the oxidation behavior of the vanillyl alcohol

Abstract

Theoretical investigation on the oxidation reaction of vanillyl alcohol is accomplished by density functional theory. The three oxidation reaction pathways were identified, and the three reactive sites on the vanillyl alcohol are H on phenolic hydroxyl group, H on hydroxymethyl group, and H on methoxyl group. Theoretical calculation and analysis were carried out about the twenty-nine possible reaction channels. The potential energy surface information of every reaction channels was obtained at the B3LYP/6–311 + G(d,p) level, including geometry structure optimization and frequency calculation of the stationary point. The oxygen reaction mechanism of vanillyl alcohol is further revealed in detail at molecular and atomic levels. The calculation results show that the H on phenolic hydroxyl group is easier to be oxidized to phenoxy radical among three reactive sites. Vanillin can produce vanillyl alcohol through a reversible process. The reaction channel of addition by oxygen on one para-position of quinone structure of phenoxy radical is more kinetically favorable than that of the two ortho-positions. Revealing the oxidation mechanism of vanillyl alcohol will provide a new understanding of the catalytic oxidation of lignin model materials and a theoretical basis for the process optimization of efficient utilization of biomass energy.