A single-step Ru/C-catalyzed strategy for selective removal of the γ-carbinol group from lignin β-O-4 linkages

A single-step removal of γ-carbinol from lignin β-O-4 linkages was reported. • Key parameters for γ-carbinol removal were systematically screened and optimized. • Ru/C system enabled efficient upgrading of monophenols from birch-derived bio-oil. • The selectivity and yield of 2,6-dimethoxy-4-ethylphenol reach 53.02% and 39.33%. • A promising route for lignin valorization was proposed. Development of efficient strategies for converting the C3 β-O-4 motif of lignin into a simplified C2 β-O-4 structure is of great significance, yet it remains a formidable challenge. Herein, we report the use of Ru/C as a catalyst to convert α-hydroxy-free C3 β-O-4 fragments into C2 β-O-4 fragments via a one-step strategy for the removal of the γ-carbinol group. A series of lignin-derived phenolic model compounds were selected to systematically investigate the effects of key reaction parameters, including temperature, reaction time, catalyst dosage, and substituent structure on the removal of the γ-carbinol group. On the basis of the obtained reaction rules and optimized parameters, the Ru/C-catalyzed system was successfully applied to the upgrading of monophenolic components in bio-oil obtained from the depolymerization of authentic birch lignin. Under optimized reaction conditions, 4-(3-hydroxypropyl)-2,6-dimethoxyphenol in the bio-oil achieved a conversion of 74.18%, affording the target product 2,6-dimethoxy-4-ethylphenol with a selectivity of 53.02% and a yield of 39.33%. This study provides a novel and efficient approach for the valorization of lignin-derived bio-oil, laying a solid foundation for the sustainable utilization of lignin resources. Download: Download high-res image (376KB) Download: Download full-size image