Rate Constants for the Reactions between OH and Perfluorinated Alkenes

The rate constants for the reactions of OH radicals with fully fluorinated alkenes containing different numbers of -CF3 groups next to olefinic carbon, CF2=CF2, CF2=CFCF3, CF3CF=CFCF3, and (CF3)2C=CFC2F5, were measured between 230 and 480 K using the flash photolysis resonance fluorescence technique to give the following expressions:
kC2F4(250-480 K) = 1.32 × 10-12 × (T/298 K)^0.9 × exp(+600 K/T) cm3 molecule-1 s-1,
kC3F6(230-480 K) = 9.75 × 10-14 × (T/298 K)^1.94 × exp(+922 K/T) cm3 molecule-1 s-1,
ktrans-C4F8(230-370 K) = 7.50 × 10 × (T/298 K)^1.68 × exp(+612 K/T) cm3 molecule-1 s-1,
kcis-C4F8(230-370 K) = 2.99 × 10-14 × (T/298 K)^2.61 × exp(+760 K/T) cm3 molecule-1 s-1, and
kC6F12(250-480 K) = 2.17 × 10-15 × (T/298 K)^3.90 × exp(+1044 K/T) cm3 molecule-1 s-1.
The kinetics of the OH reaction in an industrial sample of octofluoro-2-propene (a mixture of the cis- and trans-isomers of CF3CF=CFCF3) was studied to determine the “effective” reaction rate constant for the typically industrial mixture: k<C4F8>(230-480 K) = 7.89 × 10-14 × (T/298 K)^1.71 × exp(+557 K/T) cm3 molecule-1 s-1. On the basis of these results, the atmospheric lifetimes were estimated to be 1.2, 5.3, 21, 34, and 182 days for CF2=CF2, CF3CF=CF2, trans-CF3CF=CFCF3, cis-CF3CF=CFCF3, and (CF3)2C=CFC2F5, respectively. The general pattern of halolalkene reactivity toward OH is discussed.