Tetramethylammonium hydroxide (TMAH) thermochemolysis of lignin: Improvement of the distribution profile of products derived from β-aryl ether subunits

Tetramethylammonium hydroxide (TMAH) thermochemolysis of softwood lignin provides Z/E-1-(3,4-dimethoxyphenyl)-2-methoxyethene (5) and erythro/threo-1-(3,4-dimethoxyphenyl)-1,2,3-trimethoxypropane (9), as products derived from β-aryl ether subunits. To increase the contribution of 9, Japanese cedar (Cryptomeria japonica) wood meals were derivatized by: (1) diazomethane-methylation, (2) acetylation and (3) a combination of the methylation and acetylation. The non-derivatized (control) and derivatized wood meals were moistened with a 25% TMAH aqueous solution, dried at 80 °C for 15 min and followed by TMAH thermochemolysis at 315 °C for 4 s. Although all samples produced 5 and 9, their yields and the 9/5 ratios differed. The diazomethane-methylated cedar provided the largest values for the 5 + 9 yield, the 9 yield and the 9/5 ratio. The 5 + 9 yield from the diazomethane-methylated cedar was 1.17 that from the control and the 9 yield of the methylated cedar was 1.82 that of the control. The 9/5 ratios were 1.80 and 0.71 for the diazomethane-methylated cedar and the control, respectively. Acetylated cedars provided a lower 5 + 9 yield and a lower 9/5 ratio than the control.