Protection Group Effects During α,γ-Diol Lignin Stabilization Promote High-Selectivity Monomer Production

Protection groups were introduced during biomass pretreatment to stabilize lignin's ,-diol group during its extraction and prevent its condensation. Acetaldehyde and propionaldehyde stabilized the ,-diol without any aromatic ring alkylation, which significantly increased final product selectivity. The subsequent hydrogenolysis catalyzed by Pd/C generated lignin monomers at near-theoretical yields based on Klason lignin (48% from birch, 20% from spruce, 70% from high-syringyl transgenic poplar), and with high selectivity to a single 4-n-propanolsyringol product (80%) in the case of the poplar. Unlike direct hydrogenation of native wood, hydrogenolysis of protected lignin with Ni/C also led to high selectivity to this single product (78%), paving the way to high-selectivity lignin upgrading with base metal catalysts. The use of extracted lignin facilitated valorization of polysaccharides, leading to high yields of all three major biomass polymers to a single major product.