Takashi Hosoya, K. Kawase, Yukimichi Hirano, Mizuki Ikeuchi, H. Miyafuji
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引用次数: 4
摘要
碱性好氧氧化是将木质素转化为低分子量酚类,特别是4-羟基苯甲醛的一种很有前途的方法。我们之前的研究报道了软木木质素样品与大体积阳离子Bu4N+的氧化,促进了香兰素(4-羟基-3-甲氧基苯甲醛)的选择性生产。本研究研究了在NaOH水溶液中,在环聚醚存在的情况下,从日本杉木(Cryptomeria japonica)中的天然软木木质素中生产香兰素,我们期望Na+-聚醚配合物具有类似于Bu4N+的作用。木粉(10mg)在4.0 M NaOH aq (2.0 mL)中在120°C下在空气中氧化得到香兰素,木质素产率为6.2 wt%,通过添加15-冠-5(1,4,7,10,13-五氧环十五烷)将香兰素产率提高到15.2%。另一方面,添加了15-冠-5的非环类似物四乙二醇二甲醚,则没有观察到这种效果。木质素模型化合物的机理研究表明,配合物阳离子对香兰素前体的稳定作用是冠醚提高香兰素产率的原因之一。这与之前报道的Bu4N+的影响相似,表明大尺寸阳离子物种可以有效控制好氧氧化。
Alkaline aerobic oxidation of native softwood lignin in the presence of Na+-cyclic polyether complexes
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, Bu4N+, 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 Bu4N+. 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 Bu4N+ reported previously, suggesting effective control of aerobic oxidation by large size cationic species.
期刊介绍:
The Journal of Wood Chemistry and Technology (JWCT) is focused on the rapid publication of research advances in the chemistry of bio-based materials and products, including all aspects of wood-based polymers, chemicals, materials, and technology. JWCT provides an international forum for researchers and manufacturers working in wood-based biopolymers and chemicals, synthesis and characterization, as well as the chemistry of biomass conversion and utilization.
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