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

This research was supported by a Grant‐in‐Aid for Scientific Research (C)(2)(No. 11660164, 1999.4‐2000.3) and 21st COE program “Establishment of Sustainable Energy System” from The Ministry of Education, Culture, Sports, Science and Technology, Japan.

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 C_α‐ and C_γ‐hydroxyl groups reduced the C_β‐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 C_α‐ or C_γ‐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_γ‐elimination followed by the C_β‐O cleavage and the C_β‐O cleavage via quinone methide intermediate.

Keywords:

• Lignin
• model dimer
• regiospecifically methylated
• pyrolysis
• β‐ether
• cleavage mechanism
• side‐chain
• hydroxyl group
• hydrogen bond

Notes

This research was supported by a Grant‐in‐Aid for Scientific Research (C)(2)(No. 11660164, 1999.4‐2000.3) and 21st COE program “Establishment of Sustainable Energy System” from The Ministry of Education, Culture, Sports, Science and Technology, Japan.