Gas-phase reactivity study of a series of hydrofluoroolefins (HFOs) toward OH radicals and Cl atoms at atmospheric pressure and 298 K

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

ATMOSPHERIC ENVIRONMENT

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2014 vol. 88 p. 107 - 114

1352-2310

The relative-rate technique has been used to determine rate coefficients for the reactions of 2-fluoropropene(CH3CF=CH2); 3,3,3-trifluoro-2-(trifluoromethyl)propene ((CF3)2C=CH2) and (E/Z)-1,2,3,3,3-pentafluoropropene ((E/Z)-CF3CF=CHF) with OH radicals and Cl atoms at (298 ± 3) K and (760 ± 10) Torr total pressure of synthetic air using different reference compounds. The experiments were performed in an environmental chamber with ?in situ? FTIR spectroscopy to monitor the concentration-time profiles of the reactants. The following room temperature rate coefficients (in cm3 molecule-1 s-1) were obtained: k1(OH + CH3CF=CH2) = (1.55  0.39) × 10-11, k2 (OH + (CF3)2C=CH2) = (6.58  2.25) ×10-13 , k3 (OH + (E/Z-CF3CF=CHF; 93% E isomer) = (2.62  0.76) × 10-12 , k4 (Cl + CH3CF=CH2) = (1.64  0.26) × 10-10, k5 (Cl + (CF3)2C=CH2) =(3.50  0.85) × 10-11 and k6 (Cl + (E/Z-CF3CF=CHF; 93% E isomer) = (4.52  0.98) × 10-11. To the best of our knowledge this work provides the first kinetic study for the reactions of CH3CF=CH2 and (CF3)2C=CH2 with OH radicals and Cl atoms under atmospheric conditions. Free-energy relationships are presented, and the effect of F atom and CF3 group substitution in the hydrofluoroolefins is discussed in terms of reactivity toward both OH radicals and Cl atoms. On the basis of the kinetic measurements, the tropospheric lifetimes of CH3CF=CH2, (CF3)2C=CH2 and (E/Z)-CF3CF=CHF will primarily be determined by their reaction with hydroxyl radicals with estimated lifetimes of approximately 9 hours, 7 days and 2 days, respectively. For the reactions of the fluoroalkenes with chlorine atoms the corresponding values of the lifetimes are 7, 33, and 26 days, respectively.