Unveiling the Atmospheric Oxidation of E2CAA Initiated by Cl Radical: DFT Study

Abstract

Ethyl 2-chloroacetoacetate (CH₃C(O)CHClC(O)OCH2CH₃, E2CAA) is a class of volatile organic compound that finds its place in the atmosphere from anthropogenic sources. However, its extensive presence in industrial processes raises concerns about its environmental impact. The present study focused on investigation of atmospheric oxidation of E2CAA initiated by Cl atom. The fate of these E2CAA is however poorly understood and scarcely taken into account in atmospheric chemistry modeling. The objective of this study is to unravel the reaction mechanism, thermodynamics, and kinetics by means of theoretical method.A comprehensive theoretical investigation was conducted to elucidate the mechanism, kinetics, and thermochemistry of the gas-phase reactions between E2CAA and Chlorine radical using the M06-2X functional. The most thermodynamically stable conformer of E2CAA was identified at ambient temperature. Four primary hydrogen abstraction pathways were characterized, each proceeding through the formation of a pre-reactive complex, indicating that the reactions follow an indirect hydrogen abstraction mechanism. Rate coefficients for reaction pathways were calculated for the first time over a temperature range of 250–450 K using Canonical Transition State Theory (CTST). Based on these kinetic results, the atmospheric lifetime of E2CAA was estimated to be approximately 2.68 days.