Low-temperature degradation of lignin in aprotic solvent system for preparation of monophenolic platform chemicals

Abstract

Lignin alkaline degradation provides a potential sustainable strategy to produce aromatic compounds from lignocellulosic biomass. However, current alkaline degradation systems of lignin suffer from low selectivity and low yield because of complex reaction pathways and self-condensation of degradation products at high temperature. In this study, an EtONa-THF/DMSO system is constructed to selectively cleave the β-O-4 ether bond of lignin to generate benzoic acid compounds at low-temperature. The β-O-4 dimeric model compound was completely converted even at 0 °C, yielding 67.7 wt% of monomers. The isolated lignin gave a 20.3 wt% yield (almost 100 % of theoretical yield) of benzoic acid compounds with 100 % selectivity at 50 °C. Molecular dynamics calculation revealed that the formation of hydrogen network between lignin and solvent was less intense in aprotic solvent. DFT calculation revealed possible reaction pathways and showed a small energy gap between essential intermediates. These analyses provided a reasonable explanation to the high reactivity of β-O-4 structure under such reaction condition.