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 Cl-2/CF3CF=CH2/reference/N-2/O-2 mixtures. At 300-400 K in the presence of >20 Torr O-2, k(1) = 1.2 x 10(-11) e((+1100/RT)) cm(3) molecule(-1) s(-1). In N-2 diluent, k(1) has a sharp negative temperature coefficient resulting from the relatively small exothermicity of the following reactions: (la) Cl + CF3CF=CH2 <-> CF3CFClCH2(center dot); (1b) Cl + CF3CF= CH2 <-> CF3CF(center dot)CH2Cl (reaction 1), which were determined in these experiments to be similar to 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 Cl-2 (k(2)) or O-2 (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 k1 on the O-2 concentration. Products measured by GC/FID as a function of temperature are CF3CFCICH2Cl, CF3COF, and CH2Cl2. The mechanism leading to these products is discussed. The rate constant for the reaction Cl + CF3CFCICH2Cl (k(11)) was measured as a function of temperature (300-462 K) at 760 Ton to be k(11) = 8.2 x 10(-12) e(-(4065/RT)) cm(3) 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)).