Theoretical Investigation on the Mechanism and Kinetics of Atmospheric Reaction of MethylDichloroacetate with Hydroxyl Radical.
Authors of this article are:
Gnanaprakasam M, Lakshmanan S, Senthilkumar K.
A summary of the article is shown below:
The atmospheric reaction of methyldichloroacetate (MDCA) with OH radical is studied using electronic structure calculations. Five different pathways were considered for the initial reactions, which results in the formation of alkyl radical of MDCA along with H2O, HOCl, and CH3O•. Among the five pathways studied, α-carbon atom (-CHCl2 site) of H-atom ion reaction which leads to the formation of the alkyl radical intermediate, •CCl2C(O)OCH3 (I1) is found to be more favourable with an energy barrier of 7.3 kcal/mol, and Cl-atom ion reaction is having high energy barrier of 21.3 kcal/mol at M06-2X/ 6-311++G(2df,2p) level. The calculated thermochemical parameters show that except Cl-atom ion channel the other initial reaction channels are highly exothermic. The rate constant is calculated for the initial H-atom ion reactions using canonical variational transition state theory over the temperature range of 278 to 350 K. The Arrhenius plot shows positive temperature dependence for both the reactions. The results from the calculated thermochemical parameters and rate constants show that the formation of the alkyl radical intermediate (I1) is more favourable with the rate constant of 2.07 x 10-13 cm3 molecule-1 s-1 at 298 K. The calculated atmospheric life time of MDCA is 28 days at normal atmospheric OH concentration. The results obtained from secondary reactions show that the major product formed from the oxidation chemistry of MDCA is methyl-2-chloro-2-oxoacetate (or) methyl oxalyl chloride.
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