The Cl-initiated oxidation of CH2=CHOC(O)CH3 and CH2=CHCH 2 OC(O)CH3 in the troposphere: kinetics and product distribution

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

Los Cocos, C¨®rdoba

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

CLAFQO

Acetates are emitted to the atmosphere from vegetation and through their use in industry1. Another potential source is emission from automobiles; a number of acetates, including allyl (CH2=CHCH2OC(O)CH3) and vinyl acetate (CH2=CHOC(O)CH3), have been detected as products in the combustion of rape methyl esters used as fuel alternatives or additives2. The release of these volatile organic compounds (VOCs) into the atmosphere is likely to contribute to the formation of ozone and other components of photochemical smog found in urban areas through their reactions with OH and NO3 radicals as well as with O3 and Cl atoms. Chlorine atoms, can play an important role in atmospheric chemistry, especially in the marine boundary layer, since atomic Cl usually reacts much faster than OH radicals with organic compounds (VOCs). In this work, we report rate coefficients for the reactions of Cl atoms with allyl acetate (k1) and vinyl acetate (k2):                           Cl         +          CH2=CHCH2OC(O)CH3   ¡ú         products      (k1) Cl         +          CH2=CHOC(O)CH3         ¡ú         products      (k2)                                The rate coefficients were determined using the relative method. The experiments were performed at room temperature and atmospheric pressure in a large volume photoreactor using in situ FTIR analysis to monitor the decay of the organics and the reference compounds. The following room temperature rate coefficients (in cm3 molecule-1 s-1 units) were measured: k1 = (1.30¡À0.45) ¡Á 10-10, k2= (2.68¡À0.91) ¡Á 10-10 where the uncertainties are a combination of the 2¦Ò statistical errors from the linear regression analysis and a contribution to cover errors in the rate constants of the references hydrocarbons.  This is the first kinetic study of these reactions under atmospheric conditions. The effect of substituent atoms or groups on the overall rate coefficients is analyzed in comparison with literature rate coefficients for other unsaturated compounds. In addition, product identification was performed using FTIR. Based on the kinetic information and product analysis a degradation mechanism for atmospheric conditions is postulated. 1. Helmig, D., Muller, J., and Klein, W., Chemosphere , 1989; 19: 1399. 2. Ferrari, C. PhD. Thesis, Grenoble University, 1995. Acknowledgements: The authors wish to acknowledge SECYT (Argentina), CONICET (Argentina), ANPCyT (Pr¨¦stamo BID 1728/OC-AR,PICT B 25544, 2004), SECyT-UNC (C¨®rdoba, Argentina), Fundaci¨®n Antorchas (Argentina), TWAS (Italy), RSC (UK) and DAAD-PROALAR (Germany) for financial support of this research.