RELATIVE RATE CONSTANTS FOR REACTIONS OF HFC-152A, HFC-143, HFC-143A,HFC-134A, AND HCFC-124 WITH F-ATOMS OR CL-ATOMS AND FOR CF2CH3, CF2HCH2, AND CF3CFH RADICALS WITH F2, CL2, AND O2

Relative rate experiments using UV photolysis of F2 or Cl2 have been u sed to determine rate constant ratios for several hydrofluorocarbon (H FC) reactions with Cl or F atoms and for HFC alkyl radicals with molec ular halogens. For mixtures with F2 present, dark reactions are, also, observed which are attributed to thermal dissociation of the F2 to fo rm F atoms. At 296 K, the rate of reaction (1a) [CF2HCH3 + F --> CF2CH 3 + HF] relative to (1b) [CF2HCH3 + F --> CF2HCH2 + HF] is k1a/k1b = 0 .73 (+/-0.13) and is independent of T (= 262-348 K). At 296 K, the rat io of reaction (2a) [CF2HCH2F + F- products] to that of(k1a + k1b) is (k1a + k1b)/k2. = 2.7 (+/- 0.4), and for reaction (2b) [CF3CH3 + F --> products] (k1a + klb)/k2b = 22 t 12. The temperature dependence (263- 365 K) of the rate constant of reaction (3) [CF3CFH2 + Cl --> products ] relative to reaction (4) [CF3CFClH + Cl --> products] is k3/k4( +/- 10%) = 1.55 exp(-300 KIT). For the alkyl radicals formed from HFC 152a (CF2HCH2 and CF2CH3) and from HFC 134a (CF3CFH), rate constants for t he reactions with F2 and C12 were measured relative to their reactions with 02. The rate constant of reaction (5cl) [CF2CH3 + C12 --> CF2ClC H3 + Cl] relative to (5o) [CF2CH3 + 02 --> CF2(02)CH3] is k5cl/k5o(+/- 15%) = 0.3 exp(200 KIT). For reaction (5f) [CF2CH3 + F2 --> CF3CH3 F], k5f/k5o(+/- 35%) = 0.23. The ratio for reaction (6f) [CF2HCH2 + F2 --> CF2HCH2F + F] relative to (6o) [CF2HCH2 + O2 --> CF2HCH2O2] is k6 f/k6o(+/- 40%) = 1.23 exp(-730 K/T). The rate constant,ratio for react ion (8cl) [CF3CFH + Cl2 --> CF3CFClH + CI] relative to reaction (8o) [ CF3CFH + O2 --> CF3CFHO2] is k8cl/k8o(+/- 18%) = 0.16 exp(-940 K/T). F or reaction (8f) [CF3CFH + F2 --> CF3CF2H + F], k8f/k8o(+/- 35%) = 0.6 exp(-860 K/T). (C) 1993 John Wiley & Sons, Inc.