A Theoretical Investigation on Kinetics, Mechanism, and Thermochemistry of the Gas-Phase Reactions of Methyl Fluoroacetate with OH Radicals and Fate of Alkoxy Radical

Theoretical Investigations on the Mechanism and Kinetics of OH Radical Initiated Reactions of Monochloroacetic Acid

The oxidation mechanism of monochloroacetic acid (CH₂ClCOOH) by OH radical has been systematically investigated employing quantum mechanical methods coupled with kinetic calculation using canonical variational transition state theory. Three distinct transition states were identified for the titled reaction, two corresponding to the hydrogen atom abstraction and one corresponding to the chlorine atom abstraction. The rate constants of the titled reactions are computed over the temperature range 278-350 K, and the branching ratios calculated for the hydrogen atom abstraction from the -C(O)OH site and the -CH₂Cl site are 25 and 75%, respectively, at 298 K. The computed branching ratio indicates that the kinetically favorable reaction is the hydrogen atom abstraction from the -CH₂Cl site resulting in the formation of CHClC(O)OH radical, which further undergoes secondary reaction with O₂ and other atmospheric species. The calculated overall rate constant for the hydrogen atom abstraction reactions is in consistent with the reported experimental rate constant. The atmospheric lifetime of CH₂ClCOOH is found to be around 18 days.