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

Abstract

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-CH 2OH substituent predominantly gave 2,3,3′,4′-tetramethoxystilbenes involving the elimination of the γ-CH 2OH substituent, while 2– 5 with the γ-CH 3 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 CHCH 3 on ring B remained unaffected. Substituents –CH CHCH 2OH and –COOH on ring B produced the corresponding methyl ether and ester, respectively, by methylation. The –CH CHCHO substituent on ring B was converted to the –CHO substituent.