Thermochemolytic behavior of β–β lignin structures in the presence of tetramethylammonium hydroxide (TMAH)

Tetramethylammonium hydroxide (TMAH) thermochemolysis is widely used as an effective tool for characterizing hydrolyzable biopolymers such as lignin because it provides more products reflecting structural attributes of the polymer than conventional pyrolysis. However, its functions and the origins of the products are still unclear. Lignin model compounds containing a β–β linkage were subjected to TMAH thermochemolysis (500 °C/4 s) to investigate product distributions and reaction mechanisms. The methylated products were analyzed by gas chromatography/mass spectrometry (GC/MS). Pinoresinols (2,3) and syringaresinol (5) provided di-O-methylpinoresinol (4) and di-O-methylsyringaresinol (6), respectively, as the major product, and methylated monomers. The contribution of di-O-methylresinols was ca 80% in the pyrolyzates based on GC/MS signal areas. A guaiacyl synthetic lignin and a Japanese cedar (Cryptomeria japonica) wood lignin also yielded 4 in large and small abundances, respectively, due to the abundances of β–β subunits in the lignins and the interconnection modes of the β–β subunits with other subunits. The results demonstrated that the TMAH thermochemolysis method is a good tool for analyzing β–β subunits in lignins.