Arrhenius parameters for the OH-initiated degradation of methyl crotonate, methyl-3,3-dimethyl acrylate, (E)-ethyl tiglate and methyl-3-butenoate over the temperature range of 288–314 K†
The relative-rate technique has been employed to obtain rate coefficients for the reactions between the OH radical and four unsaturated esters (methyl crotonate (k1), methyl-3,3-dimethyl acrylate (k2), (E)-ethyl tiglate (k3) and methyl-3-butenoate (k4)) between 288 and 314 K in 760 Torr of synthetic air. The experiments were performed in a multiple-pass environmental chamber with in situ FTIR detection of the esters and reference compounds. The rate coefficients for the reactions displayed a negative dependence with temperature and low pre-exponential factors. The following Arrhenius expressions (in units of cm3 per molecule per s) were obtained: k1 = (3.39 ± 0.78) × 10−12 exp[(750 ± 159)/T], k2 = (2.95 ± 0.63) × 10−12 exp[(838 ± 182)/T], k3 = (1.49 ± 0.56) × 10−12 exp[(522 ± 114)/T] and k4 = (1.90 ± 1.25) × 10−12 exp[(834 ± 185)/T]. The kinetic results are in agreement with a mechanism involving mainly OH radical addition to the double with the reversible formation of an OH-adduct. Atmospheric implications are discussed with particular reference to the rate coefficients obtained as a function of the temperature.