Lignin valorization remains a key challenge in the development of sustainable biorefineries. However, the inevitable condensation of lignin during the fractionation of lignocellulosic biomass results in lower lignin yield and increased heterogeneity, thereby limiting its applications. Acidic thiourea fractionation has been shown to produce high-yield, light-colored lignin under relatively mild conditions. To investigate lignin reactivity and fractionation behavior, two model compounds (a β-O-4’ dimer and a lignan-based tetramer with four aromatic rings) were synthesized, and both model compounds were then subjected to an acidic thiourea fractionation process. Unlike the traditional use of lignin dimer models, we incorporated a lignan structure into the model to develop a lignin tetramer featuring both lignan and β-O-4 linkages. The successful synthesis of the model compound with a lignan structure was confirmed using various characterization methods, including nuclear magnetic resonance (NMR) and Ultra-performance liquid chromatography-mass spectrometry (UPLC-MS). The mechanistic evaluation indicated that thiourea did not cleave the β-O-4’ ether linkage but influenced the chemical environment of the α- and γ-positions. Significant shifts in the α-, β-, and γ-protons suggest that thiourea interacts with hydroxyl-containing structures, leading to possible modifications in these regions. The development of new lignin-structured model compounds has significantly advanced research in lignin chemistry. It not only enhances the understanding of lignin degradation, separation, and conversion mechanisms but also provides theoretical support and an experimental foundation for its efficient utilization.
WWSC is a joint research center between KTH Royal Institute of Technology, Chalmers University of Technology and Linköping University. The base is a donation from the Knut and Alice Wallenberg Foundation. The Swedish industry is supporting WWSC via the platform Treesearch.
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