Isomerisation of CF₂ClCH₂Cl and CFCl₂CH₂F by Interchange of Cl and F Atoms with Analysis of the Unimolecular Reactions of Both Molecules

Abstract

The recombination of CF(2)Cl with CH(2)Cl and CFCl(2) with CH(2)F were employed to generate CF(2)ClCH(2)Cl* and CFCl(2)CH(2)F* molecules with 381 and 368 kJ mol(-1), respectively, of vibrational energy in a room-temperature bath gas. The unimolecular reactions of these molecules, which include HCl elimination, HF elimination, and isomerisation by interchange of chlorine and fluorine atoms, were characterized. The three rate constants for CFCl(2)CH(2)F were 2.9×10(7), 0.87×10(7) and 0.04×10(7) s(-1) for HCl elimination, isomerisation and HF elimination, respectively. The isomerisation reaction must be included to have a complete characterization of the unimolecular kinetics of CFCl(2)CH(2)F. The rate constants for HCl elimination and HF elimination from CF(2)ClCH(2)Cl were 14×10(7) and 0.37×10(7) s(-1), respectively. Isomerisation that has a rate constant less than 0.08×10(7) s(-1) is not important. These experimental rate constants were matched to calculated statistical rate constants to assign threshold energies, which are 264, 268, and 297 kJ mol(-1), respectively, for isomerisation, HCl elimination, and HF elimination for CFCl(2)CH(2)F and 314, 251, and 289 kJ mol(-1) in the same order for CF(2)ClCH(2)Cl. Density functional theory was used to evaluate the models that were needed for the statistical rate constants; the computational method was B3PW91/6-31G(d',p'). Threshold energies for the unimolecular reactions of CF(2)ClCH(2)Cl and CFCl(2)CH(2)F are compared to those for CF(2)ClCH(3) and CFCl(2)CH(3) to illustrate the elevation of threshold energies by F- or Cl-atom substitution at the beta carbon atom (identified by C(H)). The DFT calculations systematically underestimate the threshold energy for HCl elimination.

Experimental and Computational Studies of Unimolecular 1,1-HX (X = F, Cl) Elimination Reactions of C2D5CHFCl: Role of Carbene:HF and HCl Adducts in the Exit Channel of RCHFCl and RCHCl2 Reactions

“…Of course, substitution of a Cl-atom for a D atom in CD 3 CHFCl was expected to lower both E 0 (2,1-HX) and increase the branching for 1,1-HX processes for CD 2 ClCHFCl. The effect upon E 0 (2,1-HCl) upon substituting a F atom for a H atom on the C Cl atom is not fully understood. ,,, The current study can be compared to C 2 D 5 CH 2 Cl, which has a rate constant of 2.2 × 10 8 s –1 for < E > = 91 kcal mol –1 and E 0 = 54 kcal mol –1 . These results suggest that the F atom slightly increased the threshold energy for C 2 D 5 CHFCl in contradistinction to CD 3 CHFCl, which favored a larger increase in E 0 relative to CH 3 CH 2 Cl.…”

“…In the present work, we provide another example of 1,1-HCl elimination in competition with 2,1-DCl elimination by a gas-phase chemical-activation study of C 2 D 5 CHFCl*. The 2,1-DCl elimination reaction also is of interest because the effect on the threshold energy when the F atom is on the carbon that is losing a Cl-atom ,, remains to be defined. The competing 2,1-DF and 1,1-HF reactions are less important, but they are observed.…”

Unimolecular Rate Constants for the HF and HCl Elimination Reactions from Chemically Activated CF2ClSH

“…Therefore, we calculated the k HF = P(D/S) k M for the highest pressure where CFCl=S and CF 2 ClSH could be measured. Equation and the following collision diameters and ε/ k values: CF 2 ClSH (5.4 Å and 410 K), H 2 S (3.7 Å and 302 K), (CF 2 Cl) 2 C=O (5.2 Å and 420 K), and SF 6 (5.2 Å and 212 K) give k M = 1.6 × 10 7 Torr −1 s −1 .…”

“…Typically , our experimental rate constants have error limits of ±20–30%, but these are obviously much greater because of uncertainty associated with (a) calibrating the MS detector, (b) calculating k M , (c) scatter of the experimental data, and (d) the effect of cascade deactivation. We believe the largest uncertainty arises from the scatter in the data.…”

Combustion-Based Transportation in a Carbon-Constrained World—A Review

“…In the current scenario, low-load GCI is a big challenge and efforts are being made to improve the combustion stability. Selection of low RON gasoline could avert this problem and RON 70 gasoline is an ideal candidate for GCI investigation (Solaka et al 2012).…”