Rate constants and Arrhenius parameters for the reactions of OH radicals and Cl atoms with CF3CH2OCHF2, CF3CHClOCHF2 and CF3CH2OCClF2, using the discharge-flow/resonance fluorescence method

Abstract

Rate constants have been determined for the reactions of OH radicals and Cl atoms with the three partially halogenated methyl-ethyl ethers, CF 3 CH 2 OCHF 2 , CF 3 CHClOCHF 2 and CF 3 CH 2 OCClF 2 , using discharge-flow techniques to generate the OH radicals and the Cl atoms and resonance fluorescence to observe changes in their relative concentrations in the presence of added ether. For each combination of radical and ether, experiments were carried out at three temperatures between 292 and 410 K, yielding the following Arrhenius expressions for the rate constants within this range of temperature: OH + CF 3 CH 2 OCHF 2 : k = (2.0 ± 0.8) × 10 -11 exp( -2110 ± 150 K / T) cm 3 molecule -1 s -1 OH + CF 3 CHClOCHF 2 : k = (4.5 ± 1.3) × 10 -13 exp( -940 ± 100 K / T) cm 3 molecule -1 s -1 OH + CF 3 CH 2 OCClF 2 : k = (1.6 ± 0.6) × 10 -12 exp( -1100 ± 125 K / T) cm 3 molecule -1 s -1 Cl + CF 3 CH 2 OCHF 2 : k = (6.1 ± 1.4) × 10 -12 exp( -1830 ± 90 K / T) cm 3 molecule -1 s -1 Cl + CF 3 CHClOCHF 2 : k = (7.8 ± 2.6) × 10 -11 exp( -2980 ± 130 K / T) cm 3 molecule -1 s -1 Cl + CF 3 CH 2 OCClF 2 : k = (2.2 ± 0.2) × 10 -11 exp( -2700 ± 40 K / T) cm 3 molecule -1 s -1 2 Paper for PhysChemChemPhys on OH, Cl + ethersThe results are compared with those obtained previously for the same and related reactions of OH radicals and Cl atoms, and the atmospheric implications of the results are considered briefly. IntroductionPartially halogenated ethers have uses both as potential replacements for chlorofluorocarbons 1 (CFCs) in a number of applications, and as quite widely used anaesthetics. 2 Consequently, studies of the kinetics of the reactions of these compounds with free radicals, especially OH, are useful, since the results aid our understanding of their atmospheric chemistry and allow their atmospheric lifetimes to be estimated. Less directly, they assist with the interpretation of laboratory experiments that are designed to reveal the mechanisms by which these ethers break down in the atmosphere. 3 Finally, evaluation of the rate constants and activation energies for these reactions can help with the construction of structure-activity relationships. In this context, one can, for example, compare the kinetic parameters for the reactions of a given radical with the substituted ethers with those for the reactions of the same radical with the corresponding substituted alkanes where the ether linkage is absent. Alternatively, one can explore how substitution of fluorine or chlorine atoms for hydrogen atoms affects the susceptibility of the molecule to attack by, for example, OH radicals or Cl atoms.Hydrofluoroethers (HFEs) are favoured as possible CFC replacements over other halogenated ethers as they contain no chlorine, which if released as atoms can catalytically destroy stratospheric ozone. Of course, HFEs are volatile and will inevitably be released into the atmosphere during use. Their oxidation, initiated predominantly by OH radicals, will lead to the formation of fluorinated esters and fluorinated formates. 4,5 The likely i...

Atmospheric chemistry of CH2FOCH2F: Reaction with Cl atoms and atmospheric fate of CH2FOCHFO· radicals

“…As shown in Fig. 7, a similar correlation exists for HFEs [1][2][3][4][5][6][7]9,10,13,20,30,31]. Linear least-squares analysis of the data in Fig.…”

Theoretical study of the reactions CF3CH2OCHF2 + OH/Cl and its product radicals and parent ether(CH3CH2OCH3) with OH

“…For the reaction CF 3 CH 2 OCHF 2 with OH (R1) or Cl (R2), two H‐abstraction channels are feasible. Three experimental studies were reported for reaction R1 by Zhang et al,4 Beach et al,5 and Oyaro et al6 in the temperature range of 292–402 K, and the measured rate constants show good agreement. The kinetics of reaction R2 has attracted considerable attention experimentally.…”

“…The individual CVT/SCT rate constants of each reaction channel ( k 1a , k 1b , k 2a , k 2b and k 5a , k 5b , k 5c , k 5c′ ), the total rate constant k 1 , k 2 , k 5 , and the available experimental values5–11 are plotted in Figure 4, the temperature dependence of the k 1a / k 1 , k 1b / k 1 , k 2a / k 2 , k 2b / k 2 and k 5a / k 5 , k 5b / k 5 , k 5c / k 5 . k 5c′ / k 5 branching ratios are plotted in Figure 5.…”

“…The kinetics of reaction R2 has attracted considerable attention experimentally. Five experimental studies of the rate constants5–9 of R2 have been carried out in the temperature range of 273–398 K. Most of these results show good mutual agreement except for the values taken from ref 8,. which are about two to three times larger than the others in the measured temperature range.…”

Theoretical study and rate constants calculation for the reactions X + CF3CH2OCF3 (X = F, Cl, Br)

“…Therefore, it is important to investigate the reaction mechanism of halogen with HFEs. The reactivity of OH/Cl with HFEs has been theoretical and experimental studied in the past literatures,[1–8] and few rate constants data are available for the Cl atom reactions of CF 3 CH 2 OCH 3 ,[1] CH 3 CH 2 OCF 3 ,[1] CF 3 CH 2 OCHF 2 ,[2–4] CF 3 CH 2 OCClF 2 ,[4] and CF 3 CHFOCF 3 ,[5] the corresponding rate values at 298 K are (1.8 ± 0.9) × 10 −11 , (2.2 ± 0.8) × 10 −12 , (3.1 ± 0.1) × 10 −14 , (3.2 ± 0.2) × 10 −15 , and (3.1 ± 2.5) × 10 −14 cm 3 molecule −1 s −1 , respectively. The theoretical investigation of the reaction halogen with CF 3 CH 2 OCF 3 is desirable to give a further understanding of the mechanism of this multiple channel reaction and to evaluate the rate constant.…”