Cleaving the beta-O-4 Bonds of Lignin Model Compounds in an Acidic Ionic Liquid, 1-H-3-Methylimidazolium Chloride: An Optional Strategy for the Degradation of Lignin

The hydrolysis of beta-O-4 bonds in two lignin model compounds was studied in an acidic ionic liquid, 1-H-3-methylimidazolium chloride. The beta-O-4 bonds of both guaiacylglycerol-beta-guaiacyl ether and veratrylglycerol-beta-guaiacyl ether underwent catalytic hydrolysis to produce guaiacol as the primary product with more than 70% yield at 150 degrees C. Up to 32 wt% substrate concentration could be treated in the system without a decrease in guaiacol production. The ionic liquid could be reused without loss of activity in guaiacol production from both guaiacylglycerol-beta-guaiacyl ether and veratrylglycerol-beta-guaiacyl ether. A possible mechanism accounting for the guaiacol production is presented.