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Effect of side-chain length in lignin model compound on MnO2 oxidation: comparison of oxidations between C6-C2- and C6-C1-type compounds
Journal of Wood Science ( IF 2.2 ) Pub Date : 2021-04-07 , DOI: 10.1186/s10086-021-01964-w
Shirong Sun , Tomoya Yokoyama

Monomeric C6-C2-type lignin model compounds with a p-hydroxyphenyl (H), guaiacyl (G), syringyl (S), or p-ethylphenyl (E) nucleus (1-phenylethanol derivatives) were individually oxidized by MnO2 at a pH of 1.5 and room temperature. The results were compared with those of the corresponding C6-C1-type benzyl alcohol derivatives obtained in our recent report to examine the effect of the presence of the β-methyl group on the oxidation. The presence decelerated the oxidation regardless of the type of aromatic nucleus, although it did not change the order of the oxidation rates: G > S >> H > E. This deceleration results from the steric factor of the β-methyl group in the C6-C2-type compounds. The MnO2 oxidations of the corresponding C6-C2-type compounds deuterated at their α-(benzyl)positions showed that the magnitudes of the kinetic isotope effects are smaller than those observed in the oxidations of the corresponding C6-C1-type compounds, regardless of the type of aromatic nucleus. These smaller magnitudes suggest that the presence of the β-methyl group shifts the initial oxidation mode of MnO2 from direct oxidation of the benzyl position to one-electron oxidation of the aromatic nucleus. Only the S-type compounds afforded products via degradation of the aromatic nuclei.

中文翻译:

木质素模型化合物侧链长度对MnO 2氧化的影响:C 6 -C 2-和C 6 -C 1型化合物氧化的比较

具有对羟基苯基(H),愈创木基(G),丁香基(S)或对乙基苯基(E)核(1-苯基乙醇衍生物)的单体C6-C2型木质素模型化合物在pH值下被MnO2分别氧化1.5和室温。将结果与我们最近的报告中获得的相应C6-C1型苯甲醇衍生物的结果进行了比较,以检验β-甲基基团的存在对氧化的影响。尽管不改变氧化速率的顺序:G> S >> H> E,但存在会降低氧化速度,而与芳族原子核的类型无关:这种减速是由于C6中β-甲基的位阻因子引起的-C 2型化合物。相应的C6-C2型化合物在其α-(苄基)位置上氘代的MnO2氧化表明,无论在何种条件下,动力学同位素效应的幅度都比在相应C6-C1型化合物的氧化过程中观察到的小。芳香核的类型。这些较小的幅度表明,β-甲基的存在将MnO2的初始氧化模式从苄基位置的直接氧化转变为芳族核的单电子氧化。仅S型化合物通过芳族核的降解提供产物。这些较小的幅度表明,β-甲基的存在将MnO2的初始氧化模式从苄基位置的直接氧化转变为芳族核的单电子氧化。仅S型化合物通过芳族核的降解提供产物。这些较小的幅度表明,β-甲基的存在将MnO2的初始氧化模式从苄基位置的直接氧化转变为芳族核的单电子氧化。仅S型化合物通过芳族核的降解提供产物。
更新日期:2021-04-08
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