Abstract Radical chain reactions of a β-ether-type lignin model dimer, 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)-1-propanol, were reinvestigated at 350 °C in closed ampoule reactors under the influence of wood (Japanese cedar) pyrolysis. The formation of vinyl ether dimers and Cβ=O monomers was observed in addition to previously reported Cα=Cβ and Cα=O monomers and veratraldehyde. The vinyl ether dimer was readily hydrolyzed to the Cβ=O monomer, which suggests that the formation of the Cβ=O-type monomers, such as homovanillin from natural lignin pyrolysis, originates from the vinyl ether intermediates. Unlike the non-phenolic dimer, the corresponding phenolic dimer did not form the vinyl ether dimer and Cβ=O monomer. The results, when using Cβ-deuterium-labeled dimers, suggest that a portion of the Cα=Cβ monomer from the phenolic dimer forms via the vinyl ether intermediate, probably through conversion into quinone methide, in which the bond dissociation energy of Cβ‒O is reduced (19.1 kcal mol−1 by density functional theory calculations). This leads to the simultaneous homolytic cleavage of the Cβ‒O bond to form the Cα=Cβ monomer. Such reactions did not proceed in the pyrolysis of the non-phenolic dimer, which is not able to form the stable quinone methide intermediate. This study can provide insight into the pyrolytic conversion of lignin, particularly the formation of Cβ=O- and Cα=Cβ-types monomer.

中文翻译：

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乙烯基醚中间体对木质素模型二聚体热解过程中 Cβ=O 和 Cα=Cβ 单体形成的影响

摘要 β-醚型木质素模型二聚体 1-(3,4-二甲氧基苯基)-2-(2-甲氧基苯氧基)-1-丙醇的自由基链反应在封闭安瓿反应器中于 350 °C 的影响下进行了重新研究。木材（日本雪松）热解。除了先前报道的 Cα=Cβ 和 Cα=O 单体和藜芦醛之外，还观察到乙烯基醚二聚体和 Cβ=O 单体的形成。乙烯基醚二聚体很容易水解为 Cβ=O 单体，这表明 Cβ=O 型单体的形成，例如来自天然木质素热解的高香草醛，起源于乙烯基醚中间体。与非酚二聚体不同，相应的酚二聚体没有形成乙烯基醚二聚体和 Cβ=O 单体。结果，当使用 Cβ-氘标记的二聚体时，表明酚二聚体中的一部分 Cα=Cβ 单体通过乙烯基醚中间体形成，可能通过转化为醌甲基化物，其中 Cβ-O 的键解离能降低（密度泛函理论为 19.1 kcal mol-1计算）。这导致 Cβ-O 键同时均裂形成 Cα=Cβ 单体。这种反应在非酚二聚体的热解中没有进行，不能形成稳定的醌甲基化物中间体。这项研究可以深入了解木质素的热解转化，特别是 Cβ=O-和 Cα=Cβ-型单体的形成。这导致 Cβ-O 键同时均裂形成 Cα=Cβ 单体。这种反应在非酚二聚体的热解中没有进行，不能形成稳定的醌甲基化物中间体。这项研究可以深入了解木质素的热解转化，特别是 Cβ=O-和 Cα=Cβ-型单体的形成。这导致 Cβ-O 键同时均裂形成 Cα=Cβ 单体。这种反应在非酚二聚体的热解中没有进行，不能形成稳定的醌甲基化物中间体。这项研究可以深入了解木质素的热解转化，特别是 Cβ=O-和 Cα=Cβ-型单体的形成。