Effect of the α,β-unsaturated group on the conversion of lignin and its model dimers

Replacing α -hydroxyl group with an α , β -unsaturated group markedly enhanced the decomposition reactivity of dimer. • α , β -Unsaturated group promoted C α ─C β bond cleavage, while α -hydroxyl group led to β -O-4 bond cleavage. • α , β -Unsaturated group accelerated reaction rate ∼14-fold at 120 °C. • Dehydration of α -hydroxyl group into α , β -unsaturated group facilitated lignin depolymerization. Lignin is a promising feedstock for the production of monomeric aromatics, which can be further upgraded into valuable chemicals or fuel hydrocarbons. In this work, the effect of the α , β -unsaturated group on the conversion of lignin and its β -O-4 model dimers into monomeric aromatics was investigated. The results showed that replacing the native α -hydroxyl group with an α , β -unsaturated group markedly enhanced the decomposition reactivity of the dimer. Specifically, the α , β -unsaturated group promoted C α ─C β bond cleavage, whereas the native α -hydroxyl group led to β -O-4 bond cleavage. This significant enhancement in reactivity was consistent across varied reaction conditions and enabled near-quantitative yields of monomeric aromatics from the dimer containing the α , β -unsaturated group. Kinetic analyses indicated apparent first-order kinetic behavior for both dimers, showing that the α , β -unsaturated group accelerated the reaction rate by a factor of approximately 14 at 120 °C. Moreover, an α , β -unsaturated group generated in situ via dehydration of the α -hydroxyl group during pretreatment effectively facilitated lignin depolymerization. This work outlines a promising approach for developing efficient lignin depolymerization technologies targeting monomeric aromatics.