Preparation of hydroxycinnamic acid and hydroxycinnamate from herbal lignin in aprotic solvent under mild conditions

Herbaceous (grass-type) lignin is characterized by a high content of hydroxycinnamic acid, which are typically ester-linked to the γ-position of the lignin side chains. These hydroxycinnamate units serve as valuable precursors for a variety of fine chemicals. This study constructed a mild and efficient MeOK-DMC/THF system to cleave ester bonds in herbaceous lignin. The effects of solvent composition, alkali metal alkoxide type, reaction temperature, and biomass feedstock were systematically investigated. Under optimized conditions, bamboo lignin yielded 15.6 wt% hydroxycinnamic acid and hydroxycinnamate with a selectivity of 84.5 %, while bagasse lignin achieved a higher yield of 20.8 wt% and selectivity of 97.7 %. Model compound studies confirmed that hydroxycinnamic acid and hydroxycinnamate are generated through the γ-O ester bond cleavage reaction of hydroxycinnamic acid units. This work provides a green and scalable strategy for the valorization of renewable lignin into high-value aromatic compounds, contributing to sustainable biorefinery development.