Evaluation of Reaction Efficiency of Thioacidolysis for Cleavage of β-O-4 Interunitary Linkages by Using β-O-4 Type Artificial Lignin Polymer

Abstract

Dimeric lignin model compounds with non-phenolic and phenolic moieties and a β -O-4 type artificial lignin polymer were subjected to thioacidolysis to evaluate the reaction efficiency of thioacidolysis for cleavage of β -O-4 interunitary linkage. The obtained yields of thioethylated monomeric products from the dimeric lignin model compounds reached nearly 100% under the conventional condition, whereas that from the artificial lignin polymer was as low as 74%. Neither prolonged reaction time nor increased concentration of ethanethiol (the thioacidolysis reagent) enhanced the resulting monomer yields from the polymer (69–79%). Thioacidolysis of the lignin model compounds followed by HPSEC analysis also showed the dimeric model compounds were degraded almost quantitatively, but that the artificial lignin polymer was not. Thioacidolysis followed by desulfurization gave at least one dimeric product resulting from incomplete β -O-4 cleavage at significant yield. These results suggested the conventional thioacidolysis could not achieve quantitative cleavage of β -O-4 linkages in lignin macromolecules.