A Simple Chlorination Pathway to Access Native-Like β-O-4 Lignin and Monolignols

Extracting lignin from lignocellulosic biomass without uncontrolled condensation is challenging due to the formation of recalcitrant C-C bonds during traditional pulping and organosolv fractionation methods, leading to limited valorization of technical lignins. Emerging "lignin-first" strategies aim to prevent condensation using active stabilization methods but often yield modified protected lignin structures. Here, we report the production of an α-chloro-stabilized lignin, both directly from biomass and from acetal-protected lignin, with up to 96% α-chlorination of native α-hydroxy β-aryl ether (β-O-4) linkages. This α-chloro lignin can be converted to a native-like β-O-4 lignin via simple hydrolysis at conditions that are sufficiently mild to largely avoid lignin condensation, yielding up to 63% of the near-theoretical reductive catalytic fractionation (RCF) monomer yield on hydrogenolysis. Moreover, we used α-chloro lignin under reductive conditions to produce up to 4.2 wt % of native plant monolignols─coniferyl and sinapyl alcohol, effectively reversing lignin biosynthesis.