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Title: Radical chain reactions in pyrolytic cleavage of the ether linkages of lignin model dimers and a trimer
Authors: Watanabe, Toshihiro
Kawamoto, Haruo  kyouindb  KAKEN_id
Saka, Shiro  kyouindb  KAKEN_id
Author's alias: 河本, 晴雄
坂, 志朗
Keywords: α-ether
β-ether
hydrogen abstraction
lignin
pyrolysis
radical chain reaction
Issue Date: 1-Jul-2009
Publisher: De Gruyter
Journal title: Holzforschung
Volume: 63
Issue: 4
Start page: 424
End page: 430
Abstract: β-Ether-type dimers, [1-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-1-propanol and 1-(3, 4-dimethoxyphenyl)-2-(2-methoxyphenoxy)-1-propanol], and an α, β-diether-type trimer [1-(4-(3, 4-dimethoxybenzyloxy)-3-methoxyphenyl) -2- (2-methoxyphenoxy) -1-propanol] were pyrolyzed in a closed ampoule reactor (N₂/250–400°C/2 min). 1-Phenylpropenes (Cα=Cβ) and 1-phenylpropanones (Cα=O) were obtained as the major β-ether-cleaved products. Radical chain mechanisms are proposed in which hydrogen abstraction at the phenolic O-H and Cα-Hs occurs, respectively. The former reaction which gives rise to three radical species was much more effective than the latter. As the effective reaction increases the radical concentration, cleavage of the β-ether linkage in the phenolic dimer is achieved at a much lower temperature (260°C) than that of the non-phenolic type (360°C). Radical chain reactions are initiated in the case of the trimer with a weak Cα-O bond at lower temperature (320°C) than those of the non-phenolic (methylated) dimer, since homolysis of the Cα-O bond produces the phenoxy type dimer and 3, 4-dimethoxybenzyl radicals as initiators. However, some of the dimer phenoxyl radical was stabilized by H-abstraction (to form dimer) or by recombination with a 3, 4-dimethoxybenzyl radical (to form C-benzylated products) so that the chain depolymerization via quinone methide intermediate was suppressed.
Rights: © by Walter de Gruyter • Berlin • New York.
The full-text file will be made open to the public on 1 July 2010 in accordance with publisher's 'Terms and Conditions for Self-Archiving'.
URI: http://hdl.handle.net/2433/240652
DOI(Published Version): 10.1515/HF.2009.076
Appears in Collections:Journal Articles

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