Kinetics of the reactions of CF3C(O)OCH3 and CF2ClC(O)OCH3 with Cl atoms and OH radicals: a theoretical study

A.OLLETA AND M. TERUEL

Los Cocos, Córdoba

Conferencia; 9th Latin American Conference on Physical Organic Chemistry (CLAFQO); 2007

CLAFQO

Due to the necessity to decrease the harmful effects of chlorofluorocarbons (CFCs) and their derivatives in the atmosphere, hydrofluorinated ethers (HFEs) and hydrochlorofluorinated ethers (HCFEs) are expected to be an acceptable alternative and thus released into the atmosphere in increasing amounts1. Since hydrofluorinated esters (FESs) and hydrochlorofluorinated esters (CFESs) can be produced during the atmospheric oxidation of some HFEs and HCFEs, respectively2, it is necessary to understand the atmospheric chemistry of FESs and CFESs in order to evaluate the environmental acceptability of HFEs and HCFEs. Ab initio calculations were carried out with Møller-Plesset second perturbation theory (MP2), and the coupled cluster method (CCSD(T)) on the abstraction reaction from methyl trifluoroacetate and methyl chlorodifluoroacetate by chlorine atom and hydroxyl radical attack. Geometry optimization and vibrational frequency calculations at the MP2 and CCSD(T) level were performed on reactants, products and the transition state using the 6-31G(d) basis set.  Canonical transition-state theory was used to predict the rate constants as a function of the temperature. It was found that the kinetics parameters obtained in this work with both level of theory are in reasonable agreement with the experimental values3-5. The possibility of using relatively low level ab initio electronic structure calculations conduct at the implementation of inexpensive, semi quantitative tests tools that could help us in the prediction of the kinetics of similar processes is also discussed.  The aim of this study was to extend the existing scant data base of rate constants for the reactions of OH radicals and Cl atoms with haloesters as part of ongoing work in our laboratory regarding the atmospheric impact of oxygenated VOCs as acceptable candidates to replace the harmful CFCs and their derivatives in industrial uses. To the best of our knowledge this work provides the first temperature dependent study of the four reactions cited. 1. Finlayson-Pitts B.J., Pitts J.N., Jr.,2000. Chemistry of the Upper and Lower Atmosphere.      Academic Press, N.Y. 2. Sulbaek Andersen,  M.P., Nielsen, O. J., Wallington, T. J., Hurley, M.D., DeMoore,       G.W., 2005. J.Phys. Chem. A. 109(17), 3926-3934. 3.  Blanco M. B., Teruel M. A. , 2007.Atmos.Environ. (doi:10.106/j.atomsenv.2007.05.013). 4.  Wallington T. J., Dagaut P., Liu R., Kurylo M. J. 1988. Int. J. Chem. Kinet. 20, 177-186. 5.  Blanco M. B., Teruel M. A., 2007.Chem. Phys. Lett. (doi:10.1016/..cplett.2007.04.071). Acknowledgements The authors wish to acknowledge Facultad de Ingeniería, Universidad Nacional de Jujuy, S.S. de Jujuy, Argentina SECYT (Argentina), CONICET (Argentina), ANPCyT (Préstamo BID 1728/OC-AR,PICT B 25544, 2004), SECyT-UNC (Córdoba, Argentina), Fundación Antorchas (Argentina), TWAS (Italy) and RSC (UK) for financial support of this research.