Rate constants of the reactions of CF 2ClC(O)OCH 3 and CF 2ClC(O)OCH 2CH 3 with OH radicals and Cl atoms at atmospheric pressure

Abstract

Rate coefficients for the reactions of hydroxyl radicals and chlorine atoms with methyl chlorodifluoroacetate and ethyl chlorodifluoroacetate have been determined at 298 K and atmospheric pressure. The decay of the organics was followed using a gas chromatograph with a flame ionization detector (GC-FID), and the rate constants were determined using a relative rate method with different references. Room temperature rate constants are found to be (in cm 3 molecule −1 s −1): k 1(OH + CF 2ClC(O)OCH 3) = (1.1 ± 0.3) × 10 −13, k 2 (Cl + CF 2ClC(O)OCH 3) = (1.0 ± 0.2) × 10 −13, k 3(OH + CF 2ClC(O)OCH 2CH 3) = (5.4 ± 1.5) × 10 −13 and k 4(Cl + CF 2ClC(O)OCH 2 CH 3) = (1.5 ± 0.3) × 10 −12 with uncertainties representing ±2 σ. This is the first kinetic study of the studied reactions under atmospheric pressure. Free-energy relationships are presented, and halogen substitution in the ester is discussed in terms of reactivity with OH radicals and Cl atoms. On the basis of our kinetic measurements, the tropospheric lifetimes of CF 2ClC(O)OCH 3 and CF 2ClC(O)OCH 2CH 3 are estimated to be around 53 and 11 days, respectively, primarily due to their reaction with hydroxyl radicals in the troposphere.