Reversible addition of the OH radical to p-cymene in the gas phase: multiple adduct formation. Part 2.
Reversible addition of the OH radical to p-cymene in the gas phase: multiple adduct formation. Part 2.
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OH 自由基在气相中可逆加成到对伞花烃：形成多重加合物第 2 部分
DOI：
10.1039/c4cp02073a
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发表时间：
2014
期刊：
影响因子：
--
通讯作者：
Zetzsch
中科院分区：
文献类型：
--
作者：
Alarcón;Zetzsch
利用闪光光解-共振荧光（FP-RF）系统研究了299 ~ 349 K温度范围内对伞花烃（PC）与OH的反应。三指数函数拟合组观察到的OH衰减曲线根据一个模型，考虑可逆的除了形成两个加合物作为热不稳定的水库的OH。与本文的第1部分相比，考虑第二加合物大大改善了对我们测量的拟合，并且在299和349 K之间优化了主要途径的速率常数。OH加成和H原子夺取途径的速率常数的阿克里尼乌斯表达式为kOH = 1.9 × 10−12 exp[（610 ± 210）K/T] cm 3 s−1。加合物的单分子分解反应速率常数与其他芳香族化合物相似，具有以下阿克里尼乌斯表达式：加合物1为1 × 1012 exp[（−7600 ± 800）K/T] s−1，加合物2为4 × 1011 exp[（−8000 ± 300）K/T] s−1。加合物1和2的加合物产率分别随温度升高和降低，但在室温附近相似（约0.4）。平衡常数产生的值反应的加合物形成的熵和熵。虽然对于一个加合物合理的协议，获得与理论预测，有显着的偏差为其他加合物。这表明存在两种以上的加合物异构体，这些加合物异构体在反应模型中没有考虑。采用量子化学计算（DFT M06-2X/6- 31 G（d，p））和RRKM动力学方法研究了羟基与PC的加成反应机理。这些计算表明，与异丙基和甲基取代基的邻位OH形成的加合物是占主导地位的（55%和24%），那些与OH在ipso位置（21%和3%）。预计大部分（>90%）的ipso-C3 H7加合物通过脱烷基化反应形成对甲酚（在不存在氧的情况下）和异丙基自由基。这些理论结果与实验结果的解释吻合得很好，表明已经观察到两个邻位加合物（在实验中作为OH库出现）。
A flash photolysis-resonance fluorescence (FP-RF) system was used to study the p-cymene (PC) + OH reaction at temperatures between 299 and 349 K in helium. Triexponential functions were fitted to groups of observed OH decay curves according to a model considering a reversible addition to form two adducts as thermolabile reservoirs of OH. Compared to Part 1 of this paper, consideration of a second adduct strongly improved the fits to our measurements, and the rate constants for the major pathways were optimized between 299 and 349 K. The Arrhenius expression for the rate constant of the sum of OH addition and H-atom abstraction pathways was found to be kOH = 1.9 × 10−12 exp[(610 ± 210) K/T] cm3 s−1. Rate constants of unimolecular decomposition reactions of the adducts were similar to other aromatic compounds with the following Arrhenius expressions: 1 × 1012 exp[(−7600 ± 800) K/T] s−1 for adduct 1 and 4 × 1011 exp[(−8000 ± 300) K/T] s−1 for adduct 2. Adduct yields increased and decreased with temperature for adduct 1 and 2, respectively, but were similar (∼0.4) around room temperature. Equilibrium constants yielded values for reaction enthalpies and entropies of adduct formations. While for one adduct reasonable agreement was obtained with theoretical predictions, there were significant deviations for the other adduct. This indicates the presence of more than two adduct isomers that were not accounted for in the reaction model. Quantum chemical calculations (DFT M06-2X/6-31G(d,p)) and RRKM kinetics were employed with the aim of clarifying the mechanism of the OH addition to PC. These calculations show that formation of adducts with OH in ortho positions to the isopropyl and methyl substituents is predominant (55% and 24%) to those with OH in ipso positions (21% and 3%). A large fraction (>90%) of the ipso-C3H7 adduct is predicted to react by dealkylation forming p-cresol (in the absence of oxygen) and isopropyl radicals. These theoretical results agree well with the interpretation of the experimental results showing that the two ortho adducts (which appeared as OH reservoirs in the experiment) have been observed.
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DOI：
10.1021/jp307568c
发表时间：
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期刊：
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影响因子：
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