Hydrothermal Liquefaction of α-O-4 Aryl-Ether Linkages in Lignin.

By using lignin model compounds with relevant key characteristic structural features, the reaction pathways of alpha-O-4 aryl ether linkages under hydrothermal conditions are elucidated. Experimental results and computational modeling suggest that the alpha-O-4 linkages in lignin undergo catalyzed hydrolysis and elimination to give phenolic and alkenylbenzene derivatives as major products in subcritical water. The decreased relative permittivity of water at these high temperatures and pressures facilitates the elimination reactions. The alkyl group on the alpha-carbon and the methoxy groups on the phenyl rings both have positive effects on the rate of conversion of alpha-O-4 linkages in native lignin.