Efficient removal and direct arylation of Eucalyptus lignin by a phenol-enhanced ternary DES

Deep eutectic solvents (DESs) have emerged as promising green media for lignocellulosic biomass fractionation. However, lignin condensation during processing remains a major bottleneck, hindering efficient separation and downstream valorization. Here, a novel ternary DES composed of p -toluenesulfonic (TsOH), choline chloride (ChCl), and 4-methylguaiacol (4-MGA, a lignin-derived phenolic monomer) was developed to address this challenge. The incorporation of 4-MGA provided dual functionality: it not only promotes lignin dissolution in DES by forming hydrogen bonds and π-π interactions, but also inhibits the condensation of lignin macromolecules via an arylation strategy. Under mild conditions (90 °C, 1 h), the DES system achieved 90.1% delignification and 89.7% hemicellulose removal from Eucalyptus wood, while preserving 90.8% of the cellulose. Furthermore, the directional arylation of lignin mediated by 4-MGA offers a strategy with the potential to circumvent isomer interference in the catalytic preparation of bisphenols. This work demonstrates a rational DES design strategy for enhancing lignin extraction efficiency and opens new avenues for high-value lignin utilization in biorefinery applications.