Tropospheric Photooxidation of Fluoroesteres: product distribution at 298 K

M. B. BLANCO, IUSTINIAN BEJAN, IAN BARNES, P. WIESEN AND MARIANO A. TERUEL

Nürnberg, Germany

Congreso; 3rd EuCheMS Chemistry Congress; 2010

In order to decrease the well-established harmful depleting effects of chlorofluorocarbons (CFCs) toward the Earth´s ozone layer a significant amount of effort has gone into finding environmentally more benign alternatives to replace the CFCs. Oxygenated hydrocarbons, especially hydrofluoroethers (HFEs), have been developed as new alternatives to replace the CFCs in applications such as refrigerants, blowing and cleaning agents.[1] The main fate of HFEs in the atmosphere is reaction with OH radicals forming the corresponding hydrofluorinated esters (FESs). Hence, for a complete assessment of the atmospheric chemistry and potential detrimental environmental impacts of HFEs it is also necessary to understand the atmospheric chemistry of FESs. As for HFEs, FESs are removed from the troposphere mainly by reaction with OH radicals.[2] Reaction with Cl atoms in marine environments and heavily industrialized urban areas with high levels of chloride-containing aerosol is also removal process that needs to be considered.       In this work we report results from first-time product studies on the reactions of Cl atoms with methyl trifluoroacetate, ethyl trifluoroacetate and methyl difluoroacetate. The experiments were conducted in a 1080 L quartz-glass environmental chamber at (298±2) K and 760 Torr of air using in situ FTIR spectroscopy to monitor the organics.                 The product distribution suggests that the oxidation of fluoroesters proceeds by H-atom abstraction from the –CH3 or –CH2 groups. Under the experimental conditions the alkyl radicals formed react with molecular oxygen to give peroxy radicals which then give mainly alkoxy via peroxy-peroxy radical reactions. Formation of alkoxy radicals will also be the main pathway under atmospheric conditions. The atmospheric fate of the alkoxy radicals formed includes: a) reaction with O2 to form the corresponding anhydrides via an H- abstraction or b) an a-ester rearrangement reaction via a five-membered ring intermediate where an intramolecular H- abstraction reaction takes place between the O atom of the ester and the adjacent H of the alkyl chain to form the corresponding fluorinated acetic acid. The stability of the five-membered transition state of the α-ester rearrangement is correlated with the acid yields observed for the different fluoroacetates.