Solvent-triggered directional lignin valorization towards monomeric acetals or lignin polyols

Solvents with integrated functions enable directional lignin valorization for producing value-added chemicals or lignin polyols. In this study, a solvent-triggered directional lignin valorization process was developed based on the design of a biphasic deep eutectic solvent/dichloromethane (DES/DCM) system. The designed solvents exhibit a combined feature of chemical stabilization from ethylene glycol-based-DES and physical stabilization from a biphasic system. By establishing the DES/DCM, lignin was effectively functionalized into lignin polyols with high yield. Furthermore, by implementing a simple recycling procedure of the DCM phase, the reaction pathway was switched, leading to depolymerization and stabilization of the stabilized lignin polyols. This process resulted in an almost threefold increase in monomeric acetal yields. The effect of biphasic DES on functionalization or switched depolymerization of lignin was confirmed through model compound studies. Our findings demonstrate a directional lignin valorization route using the designed biphasic DES system, which offers potential applications in the production of value-added aromatic chemicals or potential intermediates for polymers.