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 (k(1)), methyl-3,3-dimethyl acrylate (k(2)), (E)-ethyl tiglate (k(3)) and methyl-3-butenoate (k(4))) 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 cm(3) per molecule per s) were obtained: k(1) = (3.39 +/- 0.78) x 10(-12) exp[(750 +/- 159)/T], k(2) = (2.95 +/- 0.63) x 10(-12) exp[(838 +/- 182)/T], k(3) = (1.49 +/- 0.56) x 10(-12) exp[(522 +/- 114)/T] and k(4) = (1.90 +/- 1.25)x 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.