Selective conversion of lignin to benzoquinones under ambient conditions: unlocking the potential of a single platform chemical strategy

Abstract

Lignin, a highly abundant component of lignocellulosic biomass, represents a promising sustainable source of aromatic platform chemicals. This work introduces a selective oxidative cleavage methodology to convert lignin into high-value para-benzoquinones under mild conditions. Employing Bobbitt's salt as the oxidant and leveraging a solvent-mediated side-chain exchange, the process achieves near-quantitative yields of 2,6-diethoxybenzoquinone (DEBQ) and related dialkoxybenzoquinones from 2,6-dimethoxy-4-propylphenol (DMPP). The method demonstrates exceptional selectivity, giving up to 97% DEBQ from lignin monomers and 42 wt% DEBQ from lignin oils derived by reductive catalytic fractionation (RCF) of high-S poplar biomass, surpassing previously reported approaches. The high selectivity towards oxidation of the syringol (S) unit ensures the isolation of DEBQ from a mixture of lignol monomers without chromatography, thereby enhancing potential scalability. Mechanistic studies reveal the critical roles of phenolic hydroxyl groups, benzylic hydrogens, dioxygen, and radical-mediated pathways in achieving oxidative cleavage. By coupling lignin valorization with tunable chemical derivatization, this strategy expands the utility of lignin as a renewable feedstock for pharmaceuticals, materials, and synthetic precursors and unlocks new possibilities for biomass-derived chemical production.