Atmospheric Chemistry of HCF2O(CF2CF2O)xCF2H
HCF2OðCF2CF2OÞxꢀ1CF2CF2O ! HCF2OðCF2CF2OÞxꢀ1CF2 þ COF2
Table 1. Chlorine and OH kinetic data at 295ꢁ5 K for selected HFEs and
ð16Þ
HFPEs.
HCF2OðCF2CF2OÞxꢀ1CF2 þ O2 ! HCF2OðCF2CF2OÞxꢀ1CF2O2
Compound
k(Cl)
k(OH)
(5.7ꢁ1.5)ꢀ10ꢀ14[20] (2.4ꢁ0.5)ꢀ10ꢀ15[21]
ð17Þ
ð18Þ
ð19Þ
HCF2OCF2H
HCF2OCF2OCF2H
HCF2O(CF2CF2O)CF2H
(5.0ꢁ1.1)ꢀ10ꢀ17[6]
(4.5ꢁ1.0)ꢀ10ꢀ17[6]
(2.4ꢁ0.7)ꢀ10ꢀ15[22]
(4.7ꢁ1.6)ꢀ10ꢀ15[20]
–
HCF2OðCF2CF2OÞxꢀ1CF2O2 þ ROO
! HCF2OðCF2CF2OÞxꢀ1CF2O þ RO þ O2
HCF2O(CF2CF2O)xCF2H (x ꢃ 2) (5.3ꢁ1.5)ꢀ10ꢀ17[a]
HCF2OCF2OCF2CF2OCF2H
HCF2O(CF2O)n(CF2CF2O)mCF2H
CF3OCF2H
(5.0ꢁ1.4)ꢀ10ꢀ17[17] (4.6ꢁ1.6)ꢀ10ꢀ15[20]
(5.0ꢁ1.4)ꢀ10ꢀ17[17]
–
HCF2OðCF2CF2OÞxꢀ1CF2O ! HCF2OðCF2CF2OÞxꢀ1 þ COF2
(2.3ꢁ0.3)ꢀ10ꢀ17[23] (4.9ꢁ1.0)ꢀ10ꢀ16[19]
Reactions (16) through (19) are repeated until only the ter-
minal HCF2O group remains. This group undergoes final con-
version into COF2 [reaction (20)]:
[a] Determined in this work.
Table 1 show kinetic data for the reactions of Cl atoms and
OH radicals with selected HFEs and HFPEs. Given the similar
chemical environment of the CꢀH bonds in HCF2OCF2H,
HCF2OCF2OCF2H, HCF2O(CF2CF2O)CF2H, HCF2O(CF2CF2O)xCF2H,
HCF2OCF2OCF2CF2OCF2H and HCF2O(CF2O)n(CF2CF2O)mCF2H, it is
not surprising that these compounds react with chlorine radi-
cals at similar rates. As discussed by Sander et al.,[19] the reac-
tivity of OH radicals towards HCF2OCF2H has been studied by
several groups using different experimental techniques and is
well established. As with the reaction with chlorine atoms, we
would expect the reactivity of HCF2OCF2H, HCF2OCF2OCF2H,
CF2O(CF2CF2O)CF2H, and HCF2OCF2OCF2CF2OCF2H towards OH
radicals to be comparable. Consistent with this expectation,
the reactivity reported by Cavalli et al.[20] for OH radicals to-
wards HCF2OCF2OCF2H is indistinguishable from that recom-
mended by Sander et al.[19] for HCF2OCF2H. Surprisingly, Cavalli
et al.[20] reported that OH radicals react with HCF2O-
(CF2CF2O)CF2H and HCF2OCF2OCF2CF2OCF2H at rates which are
approximately a factor of 2 greater than for HCF2OCF2H and
HCF2OCF2OCF2H. It is difficult to understand the reactivity
trend reported by Cavalli et al.[20] Close inspection of the exper-
imental data reveals that the magnitude of the consumptions
of the HFEs in the investigation by Cavalli et al.[20] was rather
small (<7%). The measurement of such small consumptions of
compounds which have broad IR absorption features is chal-
lenging and we believe that the uncertainties reported by Cav-
alli et al. are probably underestimated. We proceed with the
assumption that the reactivity of OH radicals towards the
HFPEs studied in the present work will be similar to that of OH
radicals towards HCF2OCF2H. This assumption needs to be in-
vestigated in further experimental work.
HCF2O þ O2 ! COF2 þ HO2
ð20Þ
In contrast to the situation in the experimental chamber, the
concentrations of fluorinated peroxy radicals in the atmos-
phere will be extremely small, and the self- and cross-reactions
described above will not be of atmospheric significance. In the
atmosphere the fate of the fluorinated peroxy radicals will be
reaction with NO, NO2, HO2, or CH3O2 radicals [reactions (3)–
(6)]. Reaction with NO gives the corresponding alkoxy radical
and NO2 as major products with the fluorinated organic nitrate
as a minor product. Reaction with NO2 gives a thermally unsta-
ble peroxynitrate whose fate is decomposition to reform NO2
and the peroxy radical.[14,15] Reaction with HO2 radicals gives a
hydroperoxide which will be returned back to the fluorinated
peroxy radical pool via reaction with OH radicals or photoly-
sis.[16] Reaction with CH3O2 radicals is expected to proceed via
two channels [reactions (6a) and (6b)], leading to the forma-
tion of alkoxy radicals [reaction (6a)] and a fluorinated alcohol
and formaldehyde [reaction (6b)]. The atmospheric fate of the
fluorinated alcohol is expected to be heterogeneous elimina-
tion of HF followed by hydrolysis of the acid fluoride to give a
carboxylic acid; for example, from HCF2O(CF2CF2O)xCF2H one
might expect the formation of HCF2O(CF2CF2O)xC(O)OH. The
possibility that small amounts of fluorinated acidic compounds
may be formed during the atmospheric oxidation of HFPEs is
interesting and merits further study but is beyond the scope
of the present work.
While to the best of our knowledge there are no previous
studies of HCF2O(CF2CF2O)xCF2H (x=2–4), the results from the
present work can be compared with those for similar HFPEs.
Wallington et al.[17] reported a rate-constant ratio relative to
CF3CF2H for the reactions of chlorine atoms towards HCF2O-
(CF2O)n(CF2CF2O)mCF2H of k/k12 =0.205ꢁ0.019. Tuazon[6] stud-
ied the reactivity of chlorine atoms towards HCF2OCF2OCF2H
and HCF2O(CF2CF2O)CF2H and determined rate constant ratios
of k/k12 =0.208ꢁ0.006 and 0.188ꢁ0.004, respectively. The re-
activities reported by Tuazon and Wallington et al. are, within
the experimental uncertainties, indistinguishable from that de-
termined for the HFPEs in the present work (k11/k12 =0.206ꢁ
0.016). Tuazon[6] also studied the reaction of Cl atoms with
HCF2OCF2OCF2CF2OCF2H, but for reasons which are unclear, re-
ported a reactivity of HCF2OCF2OCF2CF2OCF2H which is approx-
imately 25% below those of the other HFPEs.
Wallington et al.[17] and Tuazon[6] reported the formation of
COF2 in a near-unit yield per carbon atom from the chlorine-
atom-initiated
oxidation
of
HCF2OCF2OCF2H,
HCF2O-
(CF2CF2O)CF2H, HCF2OCF2OCF2CF2OCF2H and HCF2O(CF2O)n-
(CF2CF2O)mCF2H in 700–740 Torr of air/N2/O2 at 298 K. Cavalli
et al.[20] conducted four experiments of the chlorine-atom-initi-
ated oxidation of HCF2OCF2OCF2CF2OCF2H in 740 Torr of air
and reported the formation of COF2 in a molar yield of 300–
485%. The large range reported by Cavalli et al. presumably re-
flects difficulties in measuring the small amounts of COF2
formed (0.16–0.74 mTorr) and HFPE lost (0.03–0.24 mTorr) in
their experiments—approximately an order of magnitude
smaller than those reported herein (see Figure 3). The molar
ChemPhysChem 2010, 11, 4035 – 4041
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