Chlorine initiated photooxidation studies of hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs): Results for HCFC-22 (CHClF2); HFC-41 (CH3F); HCFC-124 (CClFHCF3); HFC-125 (CF3CHF2); HFC-134a (CF3CH2F); HCFC-142b (CClF2CH3); and HFC-152a (CHF2CH3)

✍ Scribed by E. O. Edney; D. J. Driscoll

• Publisher: John Wiley and Sons
• Year: 1992
• Tongue: English
• Weight: 741 KB
• Volume: 24
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550241205

✦ Synopsis

Data on the tropospheric degradation of proposed substitutes for ozone depleting CFCs were obtained by conducting photochemical oxidation studies of HCFCs and HFCs using long path Fourier transform infrared spectroscopy. The hydrogen abstraction reactions were initiated using C1 radicals rather than OH radicals because of the rather unreactive nature of the compounds. The experimental product yields at T = 25 % 3°C and 700 Torr of dry air were: CHClF2 (1.11 t 0.06 C(O)F,); CClFHCF3 (1.00 t 0.04 CF3C(O)F); C(0)Fz); CF3CH2F (0.16 ? 0.03 CF3CF(O), and 0.83 ? 0.22 HFC(O)), where all standard deviations are 2u. For each compound, the critical step in determining the oxidation products was the decomposition of a halogenated alkoxy radical. For HCFC-22 and HCFC-124, the major alkoxy radical decomposition route was C1 elimination. The HFC-125 product data were consistent with C-C cleavage of a two carbon alkoxy radical as the major decomposition route whereas both C-C cleavage and H abstraction by 0 2 were significant contributors to the decomposition of the HFC-134a alkoxy radical. Secondary C1 reactions in the HCFC-142b and HFC-152a experiments prevented an unambiguous determination of the decomposition modes; the data are consistent with both C -C bond scission and C1 reactions with halogenated aldehydes producing the oxidation product C(O)F1. With the exception of the HFC-134a and HFC-125 data, the proposed mechanisms can account for the major oxidation products. For HFC-134a and HFC-125, a number of product bands could not be identified. The bands are likely due to products from reactions involving the CF302 radical. 0 1992 John