Rate constants of the reactions of CF2ClC(O)OCH3 and CF2ClC(O)OCH2CH3 with OH radicals and Cl atoms at atmospheric pressure

摘要

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 + CF2ClC(O)OCH3) = (1.1 +/- 0.3) x 10(--13), k(2) (Cl + CF2ClC(O)OCH3) = (1.0 +/- 0.2) x 10(-13), k(3)(OH + CF2ClC(O)OCH2CH3) = (5.4 +/- 1 1.5) x 10(-13) and k(4)(Cl + CF2CIC(O)OCH2 CH3) = (1.5 +/- 0.3) x 10(-12) with uncertainties representing +/- 2 sigma. 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 CF2ClC(O)OCH3, and CF2ClC(O)OCH2CH3 are estimated to be around 53 and 11 days, respectively, primarily due to their reaction with hydroxyl radicals in the troposphere. (C) 2007 Elsevier B.V.. All rights reserved.