Role of side-chain hydroxyl groups in pyrolytic reaction of phenolic β-ether type of lignin dimer

Role of side-chain hydroxyl groups in pyrolytic reaction of phenolic P-ether type of lignin dimer was studied with several regiospecifically methylated dimers under the pyrolysis conditions (N-2/400 degrees C/1 min). Methylation of both C-alpha- and C-gamma-hydroxyl groups reduced the C-beta-O cleavage reactivity up to the level of the non-phenolic type. To maintain the high reactivity of guaicylglycerol-beta-guaiacyl ether, at least one hydroxyl group was required in the side-chain. These results indicate that one hydroxyl group at C-alpha- or C-gamma-position acts as a hydrogen donor during pyrolysis. Influence on the product formation also indicated that the hydrogen bond types affect the reaction sequences between the C-gamma-elimination followed by the C-beta-O cleavage and the C-beta-O cleavage via quinone methide intermediate.