Kinetics and mechanism of the reaction of OH with the trimethylbenzenes--experimental evidence for the formation of adduct isomers.
Kinetics and mechanism of the reaction of OH with the trimethylbenzenes--experimental evidence for the formation of adduct isomers.
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DOI：
10.1039/c2cp42434g
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发表时间：
2012-09
期刊：
影响因子：
--
通讯作者：
B. Bohn;C. Zetzsch
中科院分区：
文献类型：
--
作者：
B. Bohn;C. Zetzsch
在275-340 K温度范围内，利用H2O的真空紫外闪光光解共振荧光研究了OH自由基与三甲苯的可逆气相加成反应.三指数OH衰变中观察到的三甲苯的存在下，表示参与一个以上的加合物物种。推导了含两种加合异构体的微分方程组的解析解，并根据该反应模型计算了OH衰减曲线。这导致了显着的改善，拟合质量和OH速率常数的显着变化相比，以前的模型与单一的加合物物种。详细的分析仅限于1，3，5-三甲苯，其中两个OH-芳香族邻位和ipso-加合异构体的可逆形成是可行的，根据扩展的反应模型。只有在包括额外的异构化反应，一致的热化学数据，从拟合的速率常数。得到一种加成异构体和一种异构体的反应速率分别为-83 ± 7 kJ mol（-1）和-35 ± 22 kJ mol（-1）。根据文献数据，更多和更少的稳定加合物被分配到ipso和邻位加合异构体，分别。潜在的异构化排除了加合物异构体的初级产率的测定，但在任何情况下ipso加合物的形成都是次要过程。OH +1，3，5-三甲苯反应的速率常数k（OH）= 1.32 × 10（-11）cm（3）s（-1）exp（450 ± 50 K/T）。根据同样的方法，求得了1，2，3-三甲苯和1，2，4-三甲苯的OH反应速率常数分别为：k（OH）= 3.61 × 10（-12）cm（3）s（-1）exp（620 ± 80 K/T）和k（OH）= 2.73 × 10（-12）cm（3）s（-1）exp（730 ± 70 K/T）。
The reversible gas-phase addition of OH radicals to the trimethylbenzenes was investigated in pulsed experiments utilizing VUV flash-photolysis resonance-fluorescence of H(2)O in the temperature range of 275-340 K. Triexponential OH decays were observed in the presence of the trimethylbenzenes, indicating the participation of more than one adduct species. Analytical solutions for the system of differential equations with two adduct isomers were derived, and the OH decay curves were evaluated based on this reaction model. This led to significant improvements of fit qualities and notable changes in OH rate constants compared to a previous model with a single adduct species. The detailed analysis was confined to 1,3,5-trimethylbenzene where reversible formation of two OH-aromatic ortho- and ipso-adduct isomers is feasible in accordance with the extended reaction model. Only after inclusion of additional isomerization reactions, consistent thermochemical data were obtained from the fitted rate constants. Reaction enthalpies of -83 ± 7 kJ mol(-1) and -35 ± 22 kJ mol(-1) were derived for the formation of one adduct isomer and the isomerization into the other, respectively. Based on literature data, the more and less stable adducts were assigned to ipso- and ortho-adduct isomers, respectively. The potential isomerization precluded the determination of primary yields of adduct isomers but formation of the ipso-adduct in any case is a minor process. For the rate constants of the OH + 1,3,5-trimethylbenzene reaction an Arrhenius expression k(OH) = 1.32 × 10(-11) cm(3) s(-1) exp(450 ± 50 K/T) was obtained. Based on the same approach, the rate constants of the OH reactions with 1,2,3-trimethylbenzene and 1,2,4-trimethylbenzene were derived as k(OH) = 3.61 × 10(-12) cm(3) s(-1) exp(620 ± 80 K/T) and k(OH) = 2.73 × 10(-12) cm(3) s(-1) exp(730 ± 70 K/T), respectively.