Kinetics and mechanism of the gas-phase reaction of Cl atoms with benzene

TY - JOUR

T1 - Kinetics and mechanism of the gas-phase reaction of Cl atoms with benzene

AU - Sokolov, O.

AU - Hurley, M. D.

AU - Wellington, T. J.

AU - Kaiser, E. W.

AU - Platz, J.

AU - Nielsen, O. J.

AU - Berho, F.

AU - Rayez, M. T.

AU - Lesclaux, R.

PY - 1998/12/24

Y1 - 1998/12/24

N2 - The gas-phase reaction of Cl atoms with benzene has been studied using both experimental and computational methods. The bulk of the kinetic data were obtained using steady-state photolysis of mixtures containing Cl2, C6H6, and a reference compound in 120-700 Torr of N2 diluent at 296 K. Reaction of Cl atoms with C6H6 proceeds via two pathways; (a) H-atom abstraction and (b) adduct formation. At 296 K the rate constant for the abstraction channel is k1a = (1.3 ± 1.0) × 10-16 cm3 molecule-1 s-1. Phenyl radicals produced via H-atom abstraction from C6H6 react with Cl2 to give chlorobenzene. The main fate of the C6H6-Cl adduct is decomposition to reform C6H6 and Cl atoms. A small fraction of the C6H6-Cl adduct undergoes reaction with Cl atoms via a mechanism which does not lead to the production of C6H5Cl, or the reformation of C6H6. As the steady-state Cl atom concentration is increased, the fraction of the C6H6-Cl adduct undergoing reaction with Cl atoms increases causing an increase in the effective rate constant for benzene removal and a decrease in the chlorobenzene yield. Thermodynamic calculations show that a rapid equilibrium is established between Cl atoms, C6H6, and the C6H6-Cl adduct, and it is estimated that at 296 K the equilibrium constant is Kc,1b = [C6H6-Cl]/[C6H6][Cl] and lies in the range (1-2) × 10-18 cm3 molecule.1 Flash photolysis experiments conducted using C6H6/Cl2 mixtures in 760 Torr of either N2 or O2 diluent at 296 K did not reveal any significant transient UV absorption; this is entirely consistent with results from the steady-state experiments and the thermodynamic calculations. The C6H6-Cl adduct reacts slowly (if at all) with O2 and an upper limit of k(C6H6-Cl + O2) < 8 × 10-17 cm3 molecule-1 s-1 was established. As part of this work a value of k(Cl + CF2ClH) = (1.7 ± 0.1) × 10-15 cm3 molecule-1 s-1 was measured. These results are discussed with respect to the available literature concerning the reaction of Cl atoms with benzene.

AB - The gas-phase reaction of Cl atoms with benzene has been studied using both experimental and computational methods. The bulk of the kinetic data were obtained using steady-state photolysis of mixtures containing Cl2, C6H6, and a reference compound in 120-700 Torr of N2 diluent at 296 K. Reaction of Cl atoms with C6H6 proceeds via two pathways; (a) H-atom abstraction and (b) adduct formation. At 296 K the rate constant for the abstraction channel is k1a = (1.3 ± 1.0) × 10-16 cm3 molecule-1 s-1. Phenyl radicals produced via H-atom abstraction from C6H6 react with Cl2 to give chlorobenzene. The main fate of the C6H6-Cl adduct is decomposition to reform C6H6 and Cl atoms. A small fraction of the C6H6-Cl adduct undergoes reaction with Cl atoms via a mechanism which does not lead to the production of C6H5Cl, or the reformation of C6H6. As the steady-state Cl atom concentration is increased, the fraction of the C6H6-Cl adduct undergoing reaction with Cl atoms increases causing an increase in the effective rate constant for benzene removal and a decrease in the chlorobenzene yield. Thermodynamic calculations show that a rapid equilibrium is established between Cl atoms, C6H6, and the C6H6-Cl adduct, and it is estimated that at 296 K the equilibrium constant is Kc,1b = [C6H6-Cl]/[C6H6][Cl] and lies in the range (1-2) × 10-18 cm3 molecule.1 Flash photolysis experiments conducted using C6H6/Cl2 mixtures in 760 Torr of either N2 or O2 diluent at 296 K did not reveal any significant transient UV absorption; this is entirely consistent with results from the steady-state experiments and the thermodynamic calculations. The C6H6-Cl adduct reacts slowly (if at all) with O2 and an upper limit of k(C6H6-Cl + O2) < 8 × 10-17 cm3 molecule-1 s-1 was established. As part of this work a value of k(Cl + CF2ClH) = (1.7 ± 0.1) × 10-15 cm3 molecule-1 s-1 was measured. These results are discussed with respect to the available literature concerning the reaction of Cl atoms with benzene.

UR - http://www.scopus.com/inward/record.url?scp=0001168528&partnerID=8YFLogxK

U2 - 10.1021/jp9828080

DO - 10.1021/jp9828080

M3 - Journal article

AN - SCOPUS:0001168528

SN - 1089-5639

VL - 102

SP - 10671

EP - 10681

JO - Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory

JF - Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory

IS - 52

ER -