Unsaturated esters in the atmosphere: kinetics and photooxidation mechanism with OH radicals

M. B. BLANCO, I. BEJAN, I. BARNES, P. WIESEN AND M. TERUEL

Los Cocos, Córdoba

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

CLAFQO

Unsaturated esters are widely used in polymer and resin production and, as with other esters, the source of their emissions are numerous such as plastics, aircraft and electronic components1. The atmospheric degradation of the unsaturated oxygenates is controlled mainly by chemical reaction with OH and NO3 radicals and O3 molecules contributing to tropospheric ozone production and the formation of other secondary photooxidants in polluted areas2. Knowledge of both, the rate coefficients for the reactions with tropospheric oxidants like OH radicals and the degradation pathways is required to estimate the persistence, fate and harmful effects of these unsaturated oxygenated organics in the atmosphere. Rate coefficients for the gas-phase reactions of OH radicals with methyl methacrylate, butyl methacrylate, butyl acrylate and vynyl acetate were determined in the temperature range of 286-303 K and atmospheric pressure of air using the relative-rate technique with GC-FID (Argentina) and /or FTIR (Germany) analysis. Additionally, product distribution under atmospheric conditions was explored for the first time for these unsaturated esters by GC-MS3 and FTIR4 techniques. The product distribution suggests that the addition of OH to the less substituted carbon atom of the double bond is preferred, followed by decomposition of the 1-2-hydroxyalcoxy radicals formed. Kinetic data were used to estimate the atmospheric lifetimes of the esters studied. In addition, our work aims to better define the reactivity of the CH2=CHR compounds towards OH radicals as an extension of our previous work involving O(3P) additions to haloalkenes 5-6 and OH radicals and Cl atoms to acrylic acid and acrylonitrile7. In this respect, the results are also discussed in terms of the substituent effect on the reactivity of the olefinic carbons. 1. T. E. Graedel, Chemical Compounds in the Atmosphere. Academic Press, New York .1978. 2.  A. Mellouki, G.Le Bras and H. Sidebottom, Chem. Rev. 2003; 103: 5077. 3. M. B. Blanco, R. A. Taccone, S. I. Lane and M. A. Teruel, Chem. Phys. Lett. 2006; 429(4-6): 389-394. 4. Sh. Zhou, I Barnes, T. Zhu and Th. Benter. J. Phys. Chem. A .2006; 110(23): 7386-7392. 5. M. B. Blanco, R. A. Taccone, S. I. Lane and M. A. Teruel, J. Phys. Org. Chem. 2006;19(11):752-758. 6. M. B. Blanco, R. A. Taccone, S. I. Lane and M. A. Teruel, J. Phys. Chem. A.2006; 110(38): 11091-11097. 7. M. A. Teruel, M. B. Blanco and G. R. Luque, Atmos. Environ. 2007, doi:10.1016/j.atmosenv.2007.02.028. Acknowledgements The authors wish to acknowledge SECYT (Argentina), CONICET (Argentina), ANPCyT (Préstamo BID 1728/OC-AR,PICT B 25544, 2004), SECyT-UNC (Córdoba, Argentina), Fundación Antorchas (Argentina), TWAS (Italy), RSC (UK) and DAAD-PROALAR (Germany) for financial support of this research.