Alkaline hydrolysis of nonphenolic β-0-4 lignin models:: Substituent effect of the A-ring on the rate

Six nonphenolic beta-0-4 lignin models substituted on the phenyl A-ring [unsubstituted; 3,5-dimethoxyl; 3,4-dimethoxyl; 3-methoxyl; 4-methoxyl; and 4-methyl] were synthesized and the alkaline hydrolysis rates at 170 degreesC determined. Electron-withdrawing substituents enhanced the hydrolysis rate, but this effect was relatively minor. Over 90 % of the disappearance of the dimer could be accounted for by appearance of the B-ring phenolic product for all compounds, which suggests that minimal side reactions occurred.