Oxidation pathways, kinetics and branching ratios of chloromethyl ethyl ether (CMEE) initiated by OH radicals and the fate of its product radical: an insight from a computational study

Abstract

The OH-initiated oxidation reactions of chloromethyl ethyl ether (CH₂ClOCH₂CH₃) have been presented by using quantum calculation methods. The Minnesota functional (M06-2X) of the density functional theory method along with a polarization and diffuse 6-311++G(d,p) basis set is chosen for optimization and frequency calculations for H-abstractions from CH₂ClOCH₂CH₃ molecules by OH radicals. Furthermore, the CCSD(T) method along with the same basis set is used for energy refinement of all optimized structures to obtain more accurate energies of the species. Our thermo-chemical calculation results show that the C˙HClOCH₂CH₃ product radical is more stable, corresponding to hydrogen atom abstraction from the –CH₂Cl site, than others while the energy profile results indicate that the H-atom abstracted from the –OCH₂ site follows the minimum energy path compared to other channels. The rate constants are computed using canonical transition state theory (CTST) within the temperature range of 250–450 K at 1 atm. The overall rate constant (at 298 K) for the abstraction reactions is found to be consistent with the earlier reported rate constant. The percentage branching ratios of different abstraction channels and the lifetime of chloromethyl ethyl ether are also given herein. We further investigated the unimolecular decomposition pathways of the CH₂ClOCH(O˙)CH₃ radical and found that unimolecular C–C bond scission is the kinetically and thermodynamically more feasible pathway compared to other unimolecular decomposition reactions.