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：

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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。