Experimental and Theoretical Investigation of the Kinetics of the Reaction of Atomic Chlorine with 1,4-Dioxane
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- 作者：Binod R. Giri ; John M. Roscoe ; Nu虂ria Gonza虂lez-Garci虂a ; Matthias Olzmann ; John M. H. Lo ; Robert A. Marriott
- 刊名：Journal of Physical Chemistry A
- 出版年：2011
- 出版时间：May 26, 2011
- 年：2011
- 卷：115
- 期：20
- 页码：5105-5111
- 全文大小：797K
- 年卷期：v.115,no.20(May 26, 2011)
- ISSN：1520-5215
文摘
The rate coefficients for the reaction of 1,4-dioxane with atomic chlorine were measured from T = 292鈥?60 K using the relative rate method. The reference reactant was isobutane and the experiments were made in argon with atomic chlorine produced by photolysis of small concentrations of Cl2. The rate coefficients were put on an absolute basis by using the published temperature dependence of the absolute rate coefficients for the reference reaction. The rate coefficients for the reaction of Cl with 1,4-dioxane were found to be independent of total pressure from p = 290 to 782 Torr. The experimentally measured rate coefficients showed a weak temperature dependence, given by kexp(T) = (8.4鈭?.3+3.1) 脳 10鈥?0 exp(鈭?470 卤 110)/(T/K)) cm3 molecule鈥? s鈥?. The experimental results are rationalized in terms of statistical rate theory on the basis of molecular data obtained from quantum-chemical calculations. Molecular geometries and frequencies were obtained from MP2/aug-cc-pVDZ calculations, while single-point energies of the stationary points were computed at CCSD(T) level of theory. The calculations indicate that the reaction proceeds by an overall exothermic addition鈥揺limination mechanism via two intermediates, where the rate-determining step is the initial barrier-less association reaction between the chlorine atom and the chair conformer of 1,4-dioxane. This is in contrast to the Br plus 1,4-dioxane reaction studied earlier, where the rate-determining step is a chair-to-boat conformational change of the bromine鈥揹ioxane adduct, which is necessary for this reaction to proceed. The remarkable difference in the kinetic behavior of the reactions of 1,4-dioxane with these two halogen atoms can be consistently explained by this change in the reaction mechanism.