Contribution of the γ-hydroxy group to the β-O-4 bond cleavage of lignin model compounds in a basic system using tert-butoxide. (2nd September 2020)

• Record Type: Journal Article
• Authors: Zeng, Xu; Akiyama, Takuya; Yokoyama, Tomoya; Matsumoto, Yuji
• Is Part Of: Journal of wood chemistry and technology. Volume 40:Number 5(2020)
• Page Start: 348
• Page End: 360
• Publication Date: 2020-09-02
• Subjects: Base -- veratrylglycerol-β-guaiacyl ether -- veratrylglycol-β-guaiacyl ether -- dimethyl sulfoxide; Wood -- Chemistry -- Periodicals; Wood; Wood -- Chemistry; Periodicals; 674.13
• DOI: 10.1080/02773813.2020.1812660
• Languages: English
• ISSNs: 0277-3813

Abstract

Abstract: The most common non-phenolic β - O -4-type lignin model compounds with or without the γ -hydroxymethyl group (C6 -C3 - or C6 -C2 -type, respectively) were treated in a 0.5 mol/L potassium tert -butoxide in DMSO solution at 30 °C to examine the effects of presence of the group. The β - O -4 bond of the C6 -C3 -type cleaved more rapidly than the C6 -C2 -type, indicating that the γ -hydroxy group contributes to the cleavage, in contrast to their reactions in alkaline pulping processes. Furthermore, the β - O -4 bond of the threo isomer of the C6 -C3 -type cleaved more rapidly than that of the erythro isomer. This result can be attributed to the fact that the erythro isomer has the hydrogen bond between a generated alkoxide and the other hydroxy group at its α - and γ -positions in its most-preferential conformer, interfering with the β - O -4 bond cleavage. It was also suggested in treatments of their methyl-etherified derivatives at the α - or γ -hydroxy group that the contribution of the γ -hydroxy group of the threo isomer is greater than that of the erythro isomer. Detailed examination of the distribution profile of reaction products supported this greater contribution of the γ -hydroxy group of the threo isomer.