Promotive or suppressive effect of co-existing nucleophiles on lignin condensation in alkaline pulping processes
Promotive or suppressive effect of co-existing nucleophiles on lignin condensation in alkaline pulping processes
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DOI：
10.1080/02773813.2023.2183968
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发表时间：
2023-02-21
影响因子：
2
通讯作者：
Yokoyama, Tomoya
中科院分区：
文献类型：
--
作者：
Komatsu, Toshihiro;Yamauchi, Kazutaka;Yokoyama, Tomoya
本研究的目的是定量研究如何添加一个强或弱的亲核试剂（1.0 mol/L），苏打蒸煮处理（1.0 mol/L NaOH）在150 ℃影响的消失和缩合反应的一个简单的酚类木质素模型化合物，香草醇（Va）。所有观察到的现象基本上可以归因于每种试剂与衍生自Va的醌甲基化物中间体（QM（Va））的加合物形成和加合物的稳定化。当反应物为MeNH_2或Me_2NH时，加合物不可逆地稳定为其共轭碱，导致加合物的积累和随后的QM（Va）的消耗，而没有从QM（Va）重新形成Va以及Va与QM（Va）的缩合反应。当试剂为Me 3 N、CO 32或SO 42时，加合物不能稳定为共轭碱，不能生成QM（Va），从而导致QM（Va）浓度增加，促进了Va与QM（Va）的缩合反应。这些抑制和促进作用在用每种亲核试剂对Va进行相同处理而不添加NaOH时更明显，其中氢氧根阴离子的浓度低。
This study aimed to quantitatively examine how the addition of a strong or weak nucleophile (1.0 mol/L) to a soda cooking treatment (1.0 mol/L NaOH) at 150 degrees C affects the disappearance and condensation reactions of a simple phenolic lignin model compound, vanillyl alcohol (Va). All the observed phenomena could basically be attributed to the adduct formation of each reagent with the quinone methide intermediate derived from Va (QM(Va)) and the stabilization of the adduct. The adduct is irreversibly stabilized to be its conjugate base when the reagent was MeNH2 or Me2NH, resulting in the accumulation of the adduct and consequent consumption of QM(Va) without the reformation of Va from QM(Va) and condensation reactions of Va with QM(Va). The adduct is not stabilized to be its conjugate base and reproduce QM(Va) when the reagent was Me3N, CO32 over bar , or SO42 over bar (the sodium salt), resulting in the increased concentration of QM(Va) to promote the condensation reactions of Va with QM(Va). These suppressive and promotive effects were more visible in the same treatment of Va with each nucleophile without the addition of NaOH, in which the concentration of hydroxide anion was low.