Gas‐phase reactions of Cl atoms with propane, n‐butane, and isobutane

Abstract

Using the relative kinetic method, rate coefficients have been determined for the gas-phase reactions of chlorine atoms with propane, n-butane, and isobutane at total pressure of 100 Torr and the temperature range of 295-469 K. The Cl 2 photolysis (λ = 420 nm) was used to generate Cl atoms in the presence of ethane as the reference compound. The experiments have been carried out using GC product analysis and the following rate constant expressions (in cm 3 molecule −1 s −1 ) have been derived: (7.4 ± 0.2) × 10 −11 exp [−(70 ± 11)/T], Cl + C 3 H 8 → HCl + CH 3 CH 2 CH 2 ; (5.1 ± 0.5) × 10 −11 exp[(104 ± 32)/T], Cl + C 3 H 8 → HCl + CH 3 CHCH 3 ; (7.3 ± 0.2) × 10 −11 exp[−(68 ± 10)/T], Cl + n-C 4 H 10 → HCl + CH 3 CH 2 CH 2 CH 2 ; (9.9 ± 2.2) × 10 −11 exp[(106 ± 75)/T], Cl + n-C 4 H 10 → HCl + CH 3 CH 2 CHCH 3 ; (13.0 ± 1.8) × 10 −11 exp[−(104 ± 50)/T], Cl + i -C 4 H 10 → HCl + CH 3 CHCH 3 CH 2 ; (2.9 ± 0.5) × 10 −11 exp[(155 ± 58)/T], Cl + i -C 4 H 10 → HCl + CH 3 CCH 3 CH 3 (all error bars are ±2σ precision). These studies provide a set of reaction rate constants allowing to determine the contribution of competing hydrogen abstractions from primary, secondary, or tertiary carbon atom in alkane molecule.

Near-IR Cavity Ringdown Spectroscopy and Kinetics of the Isomers and Conformers of the Butyl Peroxy Radical

“…27 finds the 1-and t-butyl production to be 65(4)% and 35(3)%, while our results yield approximately 50(10)% and 50(10)%. Given the available H's in n-butane, our experimental results implies that a secondary H's is ≈4.5 more labile than a primary H. For isobutane, the corresponding ratio for tertiary to primary H's is ≈9.0.…”

Temperature‐dependent kinetics study of the gas‐phase reactions of atomic chlorine with acetone, 2‐butanone, and 3‐pentanone

“…This reactivity trend is consistent with expectations if H‐abstraction is the dominant reaction pathway. For example, in the reaction of Cl with n ‐butane, 71% of the abstraction occurs at the four secondary hydrogen sites while only 29% occurs at the six primary hydrogen sites 43,44. End products of the Cl reaction with 2‐butanone have been determined by Iwasaki et al 41, who deduce that 73 ± 9% of the overall reaction involves abstraction of a secondary hydrogen.…”

Product branching ratios in simple gas phase reactions

“…The results of the studies on propane and isobutene are summarized in Table 1. In general the agreement between the direct and indirect studies 62,63 is good and the experimental results provide a good test bed for comparing the predictions of various structure activity relationships (SAR). [64][65][66][67] Both of the temperature dependent studies show an increasing proportion of primary abstraction with increasing temperature, however, as the overall rate coefficients for the Cl reactions are either temperature independent (Cl + propane) Fig.…”