Atmospheric Chemistry of HFE-7200 (C₄F₉OC₂H₅):  Reaction with OH Radicals and Fate of C₄F₉OCH₂CH₂O(•) and C₄F₉OCHO(•)CH₃ Radicals

Abstract

Relative rate techniques were used to measure k(OH + n-C4F9OC2H5) = (6.4 ± 0.7) × 10-14 and k(OH + i-C4F9OC2H5) = (7.7 ± 0.8) × 10-14 cm3 molecule-1 s-1 at 295 K leading to estimates of ≈0.9 and 0.7 years for the atmospheric lifetimes of n-C4F9OC2H5 and i-C4F9OC2H5, respectively. A pulse radiolysis technique was used to measure k(F + HFE-7200) = (5.6 ± 2.1) × 10-11 cm3 molecule-1 s-1 (HFE-7200 = C4F9OC2H5) at 296 K. Using FTIR−smog chamber relative rate techniques the following rate constants were determined at 296 K: k(F + HFE-7200) = (5.5 ± 1.1) × 10-11, k(Cl + HFE-7200) = (2.7 ± 0.6) × 10-12, and k(Cl + C4F9OC(O)CH3) < 7 × 10-13 cm3 molecule-1 s-1. Two competing loss mechanisms for C4F9OCHO(•)CH3 radicals were identified in 700 Torr of N2/O2 diluent at 296 K; reaction with O2 and decomposition via C−C bond scission with kO2/kdecomp = 0.026 ± 0.010 Torr-1. The Cl atom initiated oxidation of HFE-7200 in N2/O2 diluent gives two products: C4F9OC(O)CH3 and C4F9OC(O)H. C4F9OC(O)CH3 is the major atmospheric oxidation product of HFE-7200; C4F9OC(O)H is a minor product. The results are discussed with respect to the atmospheric chemistry of hydrofluoroethers.