Role of Side‐Chain Hydroxyl Groups in Pyrolytic Reaction of Phenolic β‐Ether Type of Lignin Dimer

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Abstract
Role of side‐chain hydroxyl groups in pyrolytic reaction of phenolic β‐ether type of lignin dimer was studied with several regiospecifically methylated dimers under the pyrolysis conditions (N2/400°C/1 min). Methylation of both Cα‐ and Cγ‐hydroxyl groups reduced the Cβ‐O cleavage reactivity up to the level of the non‐phenolic type. To maintain the high reactivity of guaicylglycerol‐β‐guaiacyl ether, at least one hydroxyl group was required in the side‐chain. These results indicate that one hydroxyl group at Cα‐ or Cγ‐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 Cγ‐elimination followed by the Cβ‐O cleavage and the Cβ‐O cleavage via quinone methide intermediate.