Synthesis of β-O-4 type oligomeric lignin model compound by the nucleophilic addition of carbanion to the aldehyde group |
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| Authors: | Rui Katahira Hiroshi Kamitakahara Toshiyuki Takano Fumiaki Nakatsubo |
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| Institution: | (1) Division of Forest and Biomaterials Science, Graduate School of Agriculture, Kyoto University, Oiwake-cho, Kitashirakawa, Sakyo-ku, Kyoto 606-8502, Japan |
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| Abstract: | A synthetic method for obtaining lignin oligomer that contains only the β-O-4 structure is described in detail. This method consists of three reaction steps: (1) the synthesis of t-butoxycarbonylmethyl vanillin (2), (2) the nucleophilic addition oligomerization of compound 2, and (3) the reduction of the oligomeric β-hydroxyl ester. In the first step, compound 2 was synthesized from vanillin in 96.8% yield. In the second step, compound 2 was oligomerized with commercial lithium diisopropylamide (LDA) to obtain oligomeric β-hydroxyl ester (3) in 87.2% yield; the repeating units of this oligomer were joined only by β-O-4 linkages as confirmed by nuclear magnetic resonance (NMR) spectroscopy. In the third step, the oligomeric β-hydroxyl ester (3) was reduced with LiAlH4 to give compound 4 in 42.4% yield. On the basis of NMR, matrix-assisted laser desorption ionization time-of-flight mass spectrometry, and gel
permeation chromatography analyses of compound 4, it was concluded that compound 4 was an oligomeric lignin model compound containing only β-O-4 interunit linkages. The number average degree of polymerization (DPn) of obtained compound 4 was about 7.0 (M
w/M
n = 1.42). Using this oligomeric lignin model compound, conventional degradation and analytical methods will give new information. |
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| Keywords: | Lignin β -O-4 Substructure Synthesis Oligomeric lignin model compounds |
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