FTIR gas-phase kinetic study on the reactions of OH radicals and Cl atoms with unsaturated esters: Methyl-3,3-dimethyl acrylate, (E)-ethyl tiglate and methyl-3-butenoate

The relative-rate technique has been used to obtain rates coefficients for the reactions of the unsaturated esters methyl-3,3-dimethyl acrylate, (E)-ethyl tiglate and methyl-3-butenoate with OH radicals and chlorine atoms at (298 ± 2) K in synthetic air at a total pressure of (760 ± 10) Torr. The experiments were performed in an environmental chamber using in situ FTIR detection to monitor the decay of the esters relative to different reference compounds. The following room temperature rate coefficients (in units of cm3 molecule−1 s−1) were obtained: k1(OH + (CH3)2CCHC(O)OCH3) = (4.46 ± 1.05) × 10−11, k2(Cl + (CH3)2CCHC(O)OCH3) = (2.78 ± 0.46) × 10−10, k3(OH + CH3CHC(CH3)C(O)OCH2CH3) = (8.32 ± 1.93) × 10−11, k4(Cl + CH3CHC(CH3)C(O)OCH2CH3) = (2.53 ± 0.35) × 10−10, k5(OH + CH2CHCH2C(O)OCH3) = (3.16 ± 0.57) × 10−11, k4(Cl + CH2CHCH2C(O)OCH3) = (2.10 ± 0.35) × 10−10. With the exception of the reaction of Cl with methyl-3,3-dimethyl acrylate (k2), for which one determination exists in the literature, this study is the first kinetic study for these reactions under atmospheric pressure. Reactivity trends are discussed in terms of the effect of the alkyl and ester groups attached to the double bond on the overall rate coefficients towards OH radicals. The atmospheric implications of the reactions were assessed by the estimation of the tropospheric lifetimes of the title reactions.