Kinetics and mechanisms of the reactions of chlorine atoms with ethane, propane, andn-butane

Abstract

Absolute (flash photolysis) and relative (FTIR-smog chamber and GC) rate techniques were used to study the gas-phase reactions of Cl atoms with C2H6 (k1), C3H8 (k3), and n-C4H10 (k2). At 297 ± 1 K the results from the two relative rate techniques can be combined to give k2/k1 = (3.76 ± 0.20) and k3/k1 = (2.42 ± 0.10). Experiments performed at 298–540 K give k2/k1 = (2.0 ± 0.1)exp((183 ± 20)/T). At 296 K the reaction of Cl atoms with C3H8 produces yields of 43 ± 3% 1-propyl and 57 ± 3% 2-propyl radicals, while the reaction of Cl atoms with n-C4H10 produces 29 ± 2% 1-butyl and 71 ± 2% 2-butyl radicals. At 298 K and 10–700 torr of N2 diluent, 1- and 2-butyl radicals were found to react with Cl2 with rate coefficients which are 3.1 ± 0.2 and 2.8 ± 0.1 times greater than the corresponding reactions with O2. A flash-photolysis technique was used to measure k1 = (5.75 ± 0.45) × 10−11 and k2 = (2.15 ± 0.15) × 10−10 cm3 molecule−1 s−1 at 298 K, giving a rate coefficient ratio k2/k1 = 3.74 ± 0.40, in excellent agreement with the relative rate studies. The present results are used to put other, relative rate measurements of the reactions of chlorine atoms with alkanes on an absolute basis. It is found that the rate of hydrogen abstraction from a methyl group is not influenced by neighboring groups. The results are used to refine empirical approaches to predicting the reactivity of Cl atoms towards hydrocarbons. Finally, relative rate methods were used to measure rate coefficients at 298 K for the reaction of Cl atoms with 1- and 2-chloropropane and 1- and 2-chlorobutane of (4.8 ± 0.3) × 10−11, (2.0 ± 0.1) × 10−10, (1.1 ± 0.2) &times 10−10, and (7.0 ± 0.8) × 10−11 cm3 molecule−1 s−1, respectively. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 43–55, 1997.