A kinetic study of the reactions of atomic bromine with the trimethylbenzenes

Abstract

This work presents the results of kinetic measurements for the reactions of atomic bromine with the three isomers of trimethylbenzene at temperatures from 295 K to 354 K and at pressures close to atmospheric. The atomic bromine was produced by photolysis of Br₂ in a thermostated Pyrex chamber as described in our previous work. The reactants were present as dilute mixtures in argon with Br₂ in sufficient excess to scavenge the free radical products of the initiation step. Chemical analysis was by gas chromatography and the rate coefficients were calculated from the chromatographic results using the relative rate method. The experimentally measured temperature dependence of the rate coefficients for the reactions of Br with the trimethylbenzenes is given in the units cm³ molec.⁻¹ s⁻¹ by: 1,2,3-trimethylbenzene + Br, log₁₀(k) = −9.57 ± 0.43 − (996 ± 134)/T; 1,2,4-trimethylbenzene + Br, log₁₀(k) = −9.74 ± 0.29 – (968 ± 91)/T; 1,3,5-trimethylbenzene + Br, log₁₀(k) = −9.87 ± 0.26 – (1079 ± 85)/T. The enthalpies and entropies of activation for these reactions are compared to those for the reactions of Br with toluene and the xylenes.