Oxidation reaction mechanism and kinetics between OH radicals and alkyl-substituted aliphatic thiols: OH-addition pathways

IF 2.1 4区 化学 Q3 CHEMISTRY, PHYSICAL Progress in Reaction Kinetics and Mechanism Pub Date : 2019-03-26 DOI:10.1177/1468678319832382
A. Tahan, A. Shiroudi
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引用次数: 2

Abstract

Kinetic rate constants for the oxidation reactions of OH radicals with CH3SH (1), C2H5SH (2), n-C3H7SH (3) and iso-C3H7SH (4) under inert conditions (Ar) over the temperature range 252−430 K have been studied using the CBS-QB3 composite method. Kinetic rate constants under atmospheric pressure and in the fall-off regime have been estimated using transition state theory (TST) and statistical Rice–Ramsperger–Kassel–Marcus (RRKM) theory. Comparison with experiment confirms that in the OH-addition pathways 1−4 leading to the related products, the first bimolecular reaction step has effective negative activation energies around −2.61 to 3.70 kcal mol−1. Effective rate coefficients have been calculated according to a steady-state analysis of a two-step model reaction mechanism. As a result of the negative activation energies, pressures larger than 104 bar would be required to restore to some extent the validity of this approximation for all the channels. By comparison with experimental data, all our calculations for both the OH-addition and H-abstraction reaction pathways indicate that from a kinetic viewpoint and in line with the computed reaction energy barriers, the most favourable process is the OH-addition pathway to n-C3H7SH to yield the [n-C3H7SH−OH]• species, whereas under thermodynamic control of the bimolecular reactions (R−SH+OH•), the most abundant product derived from the H-abstraction pathway will be the [n-C3H7 S•+H2O] species.
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羟基自由基与烷基取代脂肪族硫醇氧化反应机理及动力学:羟基加成途径
采用CBS-QB3复合方法研究了在252 ~ 430 K的惰性条件(Ar)下OH自由基与CH3SH(1)、C2H5SH(2)、n-C3H7SH(3)和iso-C3H7SH(4)的氧化反应动力学速率常数。利用过渡态理论(TST)和统计Rice-Ramsperger-Kassel-Marcus (RRKM)理论估计了大气压力下和脱落状态下的动力学速率常数。与实验对比证实,在生成相关产物的oh加成途径1 ~ 4中,双分子反应第一步的有效活化能在−2.61 ~ 3.70 kcal mol−1之间。根据两步模型反应机理的稳态分析,计算了反应的有效速率系数。由于活化能为负,需要大于104巴的压力才能在一定程度上恢复对所有通道的这种近似的有效性。通过与实验数据的比较,我们对OH加成和h提取两种反应途径的计算表明,从动力学的角度来看,根据计算得到的反应能垒,最有利的过程是OH加成n-C3H7SH生成[n-C3H7SH−OH]•物质,而在双分子反应(R - SH+OH•)的热力学控制下,从h提取途径得到的最丰富的产物将是[n-C3H7S•+H2O]物质。
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来源期刊
CiteScore
2.10
自引率
0.00%
发文量
5
审稿时长
2.3 months
期刊介绍: The journal covers the fields of kinetics and mechanisms of chemical processes in the gas phase and solution of both simple and complex systems.
期刊最新文献
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