Oxidation of 2-propanol and cyclohexane by the reagent "hydrogen peroxide-vanadate anion-pyrazine-2-carboxylic acid": kinetics and mechanism.
Oxidation of 2-propanol and cyclohexane by the reagent "hydrogen peroxide-vanadate anion-pyrazine-2-carboxylic acid": kinetics and mechanism.
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DOI：
10.1021/jp0700884
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发表时间：
2007-07
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影响因子：
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通讯作者：
Y. Kozlov;V. B. Romakh;A. Kitaygorodskiy;P. Buglyó;G. Süss-Fink;G. B. Shul’pin
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文献类型：
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作者：
Y. Kozlov;V. B. Romakh;A. Kitaygorodskiy;P. Buglyó;G. Süss-Fink;G. B. Shul’pin
钒酸根阴离子在吡嗪-2-羧酸（PCA [等同于] pcaH）存在下有效地催化2-丙醇被过氧化氢氧化生成丙酮。紫外-可见分光光度法对反应过程的监测以及动力学研究表明，该过程的关键步骤是含pca配体的二过氧钒（V）配合物的单分子分解，生成过氧自由基HOO（.-）和V（IV）衍生物。整个过程中的限速步骤可能不是这种（快速）分解本身，而是（在此步骤之前）从配位的H2 O2分子到钒中心的pca配体的氧原子的缓慢氢转移：“（pca）（O=）V. O2H2”-->“（pca）（HO-）V-OOH”。V（IV）衍生物与新的过氧化氢分子反应生成羟基自由基（“V（IV）”+H2 O2-->“V（V）”+ HO（-）+ HO（.-）），在异丙醇的活化中具有活性：HO（.-）+ Me2CH（OH）-> H2O + Me2C（.-）（OH）。与烷烃RH在乙腈中的反应类似地进行，在这种情况下，羟基从烷烃中夺取氢原子：HO（.-）+ RH --> H2O + R（.-）。这些结论与Bell等人的结果（Khaliullin，R. Z的;贝尔，A. T.; Head-Gordon，M. J. Phys. Chem. B 2005，109，17984-17992），其最近进行了在乙腈中讨论的试剂中自由基产生机制的密度泛函理论研究。
The vanadate anion in the presence of pyrazine-2-carboxylic acid (PCA [identical with] pcaH) efficiently catalyzes the oxidation of 2-propanol by hydrogen peroxide to give acetone. UV-vis spectroscopic monitoring of the reaction as well as the kinetics lead to the conclusion that the crucial step of the process is the monomolecular decomposition of a diperoxovanadium(V) complex containing the pca ligand to afford the peroxyl radical, HOO(.-) and a V(IV) derivative. The rate-limiting step in the overall process may not be this (rapid) decomposition itself but (prior to this step) the slow hydrogen transfer from a coordinated H2O2 molecule to the oxygen atom of a pca ligand at the vanadium center: "(pca)(O=)V...O2H2" --> "(pca)(HO-)V-OOH". The V(IV) derivative reacts with a new hydrogen peroxide molecule to generate the hydroxyl radical ("V(IV)" + H2O2 --> "V(V)" + HO(-) + HO(.-)), active in the activation of isopropanol: HO(.-) + Me2CH(OH) --> H2O + Me2C(.-)(OH). The reaction with an alkane, RH, in acetonitrile proceeds analogously, and in this case the hydroxyl radical abstracts a hydrogen atom from the alkane: HO(.-) + RH --> H2O + R(.-). These conclusions are in a good agreement with the results obtained by Bell and co-workers (Khaliullin, R. Z.; Bell, A. T.; Head-Gordon, M. J. Phys. Chem. B 2005, 109, 17984-17992) who recently carried out a density functional theory study of the mechanism of radical generation in the reagent under discussion in acetonitrile.