Combinations of the Aromatic Rings in β-1 Structure Formation of Lignin Based on Quantitative Analysis by Thioacidolysis.

The amount of β-1 structures in lignin is small; however, they are assumed to significantly affect the reactivity of lignin because they form dienone structures. A method employing thioacidolysis and subsequent desulfurization yields products that can be analyzed via gas chromatography-mass spectrometry (GC-MS) to quantify these β-1 structures. However, the retention times and response factors of the reaction products have not been accurately determined thus far. Here, 12 standard compounds combined with p-hydroxyphenyl (H), guaiacyl (G), and syringyl (S) units were synthesized, and their retention times and response factors were determined through GC-MS, using selective ions. Based on these data, we also investigated the β-1 structures of lignocellulosic lignin samples. Our results clarified that the successful formation of the β-1 structure was dependent on the type of aromatic rings present; there were very few β-1 structures containing H units; and the amount of G-G type was higher and that of the heterotype, i.e., G-S type, was lower than the stochastic value.