Experimental and Theoretical Studies of the Gas-Phase Kinetics of Epichlorohydrin with Tropospheric Oxidants

Abstract

The rate coefficient of the gas-phase reaction of epichlorohydrin with the OH radical is measured by both absolute and relative rate methods. The absolute rate coefficient is found to be (3.81 ± 0.33) × 10 −13 cm 3 molecule −1 s −1 and the average relative rate coefficient is found to be (3.72 ± 1.06) × 10 −13 cm 3 molecule −1 s −1 using 1,2-dichloroethane and ethane as reference molecules. Over the temperature range of 258−333 K, the rate coefficient of epichlorohydrin and OH reaction decreases exponentially with decreasing temperature. The relative rate coefficient of the reaction of epichlorohydrin with the Cl atom is measured to be (4.22 ± 0.65) × 10 −12 cm 3 molecule −1 s −1 using 1,2-dichloroethane as the reference molecule. The net tropospheric lifetime of epichlorohydrin is calculated to be about 4 weeks. The lifetime reduces to nearly half near the marine boundary layer where the Cl reaction becomes more prominent than the OH reaction. Formic acid and acetic acid are found to be the major degradation products in the reaction of epichlorohydrin with OH radical, while formic acid and 1,3-dichloropropan-2-one are found to be major products in the reaction of epichlorohydrin with Cl atom. The theoretical OH rate coefficient using transition-state theory with the Wigner tunneling correction was calculated to be 1.71 × 10 −13 cm 3 molecule −1 s −1 at 298 K. A good agreement for the activation energy was obtained between theory (6.8 kJ/mol) and experiment (∼9 kJ/mol). The ozone-creation potential of epichlorohydrin and its global warming potential are determined. Structure−reactivity relationship is discussed in the context of ring size, cyclic and acyclic ethers.