Tetramethylammonium hydroxide (TMAH) thermochemolysis of 2-arylcoumaran lignin model compounds

Phenolic 2-arylcoumarans 1-6 were used to examine the behaviors of β-5 subunits in lignin during tetramethylammonium hydroxide (TMAH) thermochemolysis. Products were monitored by gas chromatography/mass spectrometry. The process predominantly provided dimeric products with the opened hydrofuran ring. Substituent changes at the γ-position of ring A and at the 5-position of ring B had a large effect on the product compositions. 2-Arylcoumarans 1 and 6 with the γ-CH₂OH substituent predominantly gave 2,3,3′,4′-tetramethoxystilbenes involving the elimination of the γ-CH₂OH substituent, while 2-5 with the γ-CH₃ substituent gave a mixture of 2,3,3′,4′-tetramethoxy-α-methylstilbenes and α-methoxy-α-(3′,4′-dimethoxyphenyl)-β-(2,3-dimethoxyphenyl)propanes. Substituent -CH{double bond, long}CHCH₃ on ring B remained unaffected. Substituents -CH{double bond, long}CHCH₂OH and -COOH on ring B produced the corresponding methyl ether and ester, respectively, by methylation. The -CH{double bond, long}CHCHO substituent on ring B was converted to the -CHO substituent.