Thiourea dioxide as a green reductant for selective depolymerization of lignin to guaiacol

Abstract

Selective depolymerization of lignin is a key strategy for realizing high-value utilization of this natural renewable aromatic biopolymer. Degradation of lignin by the traditional technologies usually requires costly metal complex catalysts, and encounters poor monomer selectivity at present. Herein, a novel eco-friendly reduction system for high selectivity production of guaiacol directly from technical lignin by thiourea dioxide (TDO) assisted sodium hydroxide was reported. The experimental results of lignin and 2-phenoxy-1-phenylethanol depolymerization confirmed that the addition of TDO effectively promoted the cleavage of C-O bond of β-O-4-alcohols, and lignin was completely converted with minimal char formation of 2.73 wt% under relatively mild conditions. In addition, 4.91 wt% of phenolic monomers and 55.29 wt% of re-lignin were generated, and all with improved yields compared to the environment in the absence of TDO. Notably, the selectivity of guaiacol could amount to 64.77% in this reduction system, which is significantly higher than most reports of lignin depolymerization using noble metals, enabling value-increment utilization of technical lignin by means of low cost.