Temperature-dependent ozonolysis kinetics of selected alkenes in the gas phase: an experimental and structure–activity relationship (SAR) study

The kinetics of the reactions of ozone with several alkenes have been measured at atmospheric pressure between 217 and 301 K using EXTRA (EXTreme RAnge chamber). This work represents the first kinetic determinations of the system and focuses on the temperature-dependence of alkene ozonolysis, which is an important tropospheric process impacting upon climate and human health, yet few studies have investigated these reactions as a function of temperature. Temperature-dependent rate coefficients have been established for 3,3-dimethyl-1-butene, 2,4,4-trimethyl-1-pentene and 4-methyl-1-pentene at 217–301 K and atmospheric pressure. The derived Arrhenius expressions are as follows: k = (2.68+2.23−1.23) × 10−15 exp[−(16.29 ± 1.20/RT)], k = (7.31+9.39−4.05) × 10−15 exp[−(15.33 ± 1.84/RT)] and k = (5.21+2.85−1.85) × 10−15 exp[−(15.66 ± 0.87/RT)] cm3 molecule−1 s−1 for 3,3-dimethyl-1-butene, 2,4,4-trimethyl-1-pentene and 4-methyl-1-pentene, respectively. A strong linear correlation has been observed between a simple structure–activity relationship (SAR) and the activation energy, Ea, possessing an R2 value of 0.90. However, no significant correlation was observed for the A-factor. Notwithstanding, with accurate predictions of the SAR for Ea and log k298, values for the A-factor can be retrieved, and hence the prediction of k at any temperature. The newly acquired data agree well with the original SAR and suggest that the factors controlling the rate of ozonolysis reaction are captured accurately by the SAR index.