1989 Fiscal Year Final Research Report Summary
Mechanism and Control of Cleavage of the beta-O-4 Bonds in Lignin
| Project/Area Number |
63560172
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
林産学
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| Research Institution | Kyushu University |
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Principal Investigator |
SAKAI Kokki Kyushu University, Department of Forest Products, Associate Professor, 農学部, 助教授 (30015656)
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| Project Period (FY) |
1988 – 1989
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| Keywords | Lignin / beta-Aryl ether / Delignification / Cleavage / Organosolv pulping / Solvent effect / Pulping / beta-O-4 bond |
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| Research Abstract |
The beta -omicron-4 bonds in lignin and its model compounds were reductively cleaved to give eugenol and/or isoeugenol during the alcohol-bisulfite pulping at 160 ﾟC . The mechanism and the control method of this reductive cleavage has been studied using some dimeric compounds.
1. Mechanism. (1) This cleavage seems to proceed via a quinone method intermediate because non-phenolic, alpha -carbonyl and alpha -methylene models did not produce high yield of isoeugenol. Sulfonation or alkylation at alpha position of the side chain of the quinone method more or less retarded the cleavage reaction under alcohol bisulfite pulping conditions. (2) Cleavage of the beta -syringyl ether was much faster than that of the guaiacyl ether. This strongly suggests that the quinone method formation is not the rate determining step of the cleavage reaction. (3) A reaction mechanism involving single electron transfer from bisulfite anion or from bisulfite radical to the quinone method seems to explain this cleavage reaction well. The possibility of homolytic cleavage is also discussed.
2. Control. (1) The cleavage was extensive in aqueous solutions of some primary and secondary alcohols and in aqueous dimethylformamide but much less extensive in many other solvents including aqueous ethers, tertiary alcohols, ketones, carboxylic acids, amines, a phenol, and a sulfoxide. (2) Concerning solvent concentration, the cleavage proceeded most rapidly in 50 % ethanol. Thus, the cleavage can be controlled to some extents by changing solvents and their concentration. However it is necessary to inhibit sulfonation which is competitive with the cleavage. We should study to solve this problem in the future.
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