Relative Rate Study of the Kinetics, Mechanism, and Thermodynamics of the Reaction of Chlorine Atoms with CF3CFCH2 (HFO-1234yf) in 650–950 Torr of N2 or N2/O2 Diluent at 296–462 K

The rate constant of the reaction Cl + CF3CFCH2 (k 1) has been measured relative to several reference species using the relative rate technique with either gas chromatographic analysis with flame-ionization detection (GC/FID) or Fourier transform infrared (FTIR) analysis. Cl atoms were generated by UV irradiation of Cl2/CF3CFCH2/reference/N2/O2 mixtures. At 300–400 K in the presence of >20 Torr O2, k 1 = 1.2 × 10–11 e(+1100/RT) cm3 molecule–1 s–1. In N2 diluent, k 1 has a sharp negative temperature coefficient resulting from the relatively small exothermicity of the following reactions: (1a) Cl + CF3CFCH2 ↔ CF3CFClCH2(•); (1b) Cl + CF3CFCH2 ↔ CF3CF­(•)­CH2Cl (reaction 1), which were determined in these experiments to be ∼16.5 (±2.0) kcal mol–1. This low exothermicity causes reaction 1 to become significantly reversible even at ambient temperature. The rate constant ratio for the reaction of the chloroalkyl radicals formed in reaction 1 with Cl2 (k 2) or O2 (k 3) was measured to be k 2/k 3 = 0.4 e–(3000/RT) for 300–400 K. At 300 K, k 2/k 3 = 0.0026. The reversibility of reaction 1 combined with the small value of k 2/k 3 leads to a sensitive dependence of k 1 on the O2 concentration. Products measured by GC/FID as a function of temperature are CF3CFClCH2Cl, CF3COF, and CH2Cl2. The mechanism leading to these products is discussed. The rate constant for the reaction Cl + CF3CFClCH2Cl (k 11) was measured as a function of temperature (300–462 K) at 760 Torr to be k 11 = 8.2 × 10–12 e–(4065/RT) cm3 molecule–1 s–1. Rate constants relative to CH4 for the reactions of Cl with the reference compounds CH3Cl, CH2Cl2, and CHCl3 were measured at 470 K to resolve a literature discrepancy. (R = 1.986 cal K–1 mol–1).