Alkaline aerobic oxidation of native softwood lignin in the presence of Na+-cyclic polyether complexes. (2nd January 2022)

• Record Type: Journal Article
• Authors: Hosoya, Takashi; Kawase, Kei; Hirano, Yuki; Ikeuchi, Mizuki; Miyafuji, Hisashi
• Is Part Of: Journal of wood chemistry and technology. Volume 42:Number 1(2022)
• Page Start: 1
• Page End: 14
• Publication Date: 2022-01-02
• Subjects: Depolymerization -- lignin -- mechanism -- organic cation -- vanillin; Wood -- Chemistry -- Periodicals; Wood; Wood -- Chemistry; Periodicals; 674.13
• DOI: 10.1080/02773813.2021.1998127
• Languages: English
• ISSNs: 0277-3813

Abstract

Abstract: Alkaline aerobic oxidation is a promising way to convert lignin to low molecular weight phenols, especially 4-hydroxybenzaldehydes. Our previous studies reported that oxidation of softwood lignin samples with a bulky cation, Bu4 N +, facilitates selective production of vanillin (4-hydroxy-3-methoxybenzaldehyde). This study presents vanillin production from native softwood lignin in Japanese cedar ( Cryptomeria japonica ) in NaOH aq. in the presence of cyclic polyethers, with our expectation that Na + -polyether complexes exhibit effects similar to those of Bu4 N + . Oxidation of wood flour (10 mg) in 4.0 M NaOH aq. (2.0 mL) at 120 °C under air gave vanillin with 6.2 wt% lignin-based yield, which was raised to 15.2 wt% by the addition of 15-crown-5 (1, 4, 7, 10, 13-pentaoxacyclopentadecane). On the other hand, such effect was not observed with the addition of tetraethylene glycol dimethyl ether, a non-cyclic analog of 15-crown-5. Mechanistic study with a lignin model compound revealed that stabilization of a vanillin precursor by the complex cation was a reason for the increased vanillin yield exhibited by the crown ether. This is similar to the influence of Bu4 N + reported previously, suggesting effective control of aerobic oxidation by large size cationic species.