Theoretical study of the OH-initiated atmospheric oxidation mechanism of perfluoro methyl vinyl ether, CF₃OCFCF₂

Abstract

Product formation in the reaction of perfluorinated methyl vinyl ether, CF 3 OCFQCF 2 , with OH radicals is studied theoretically using the M06-2X/aug-cc-pVTZ and CCSD(T) levels of theory. The stable endproducts in an oxidative atmosphere are predicted to be perfluorinated methyl formate, CF 3 OCFO, and fluorinated glycolaldehyde, CFOCF 2 OH, both with CF 2 O as coproduct. The prediction of glycolaldehyde as a product contrasts with experimental data, which found perfluoro glyoxal, CFOCFO, instead. The most likely explanation for this apparent disagreement is conversion of CFOCF 2 OH to CFOCFO, e.g. by multiple catalytic agents present in the reaction mixture, wall reactions, and/or photolysis. The formation routes for the glyoxal product proposed in earlier work appear unlikely, and are not supported by theoretical or related experimental work.

Absolute and relative-rate measurement of the rate coefficient for reaction of perfluoro ethyl vinyl ether (C2F5OCFCF2) with OH

“…Since its lifetime is short, PEVE is unlikely to have a significant global warming potential. The atmospheric, OH-initiated degradation of PEVE is likely to lead to fluorinated oxygenates such as CF 2 O and C 2 F 5 OCFO, 10,23 though this theoretical result awaits confirmation in experimental product studies, which are presently being undertaken in this laboratory.…”

“…The negative temperature dependence stems from the formation of an association complex as described for other fluorinated, vinyl ethers. 10,23 The quoted errors are 2s (statistical only). We adopt the temperature dependence (480/T) and modify the pre-exponential factor slightly to give the average room temperature rate coefficient from all experiments and obtain: k 1 (200-300 K) = 6.0 Â 10 À13 exp(480/T) for use in calculation of the rate coefficient at any temperature in the range listed, where the uncertainty will be 10%, independent of temperature.…”

“…The change in the negative activation energy is however more obvious, likely reflecting the formation of lower energy transition states on the exit channel to product formation for the larger association complexes formed from addition of OH to the vinyl ethers, though this has not been predicted by quantum chemical calculations for PMVE and PEVE. 10,23 Table 3 also lists room temperature rate coefficients for the reaction of non-fluorinated alkyl vinyl ethers. The rate coefficients for the non-fluorinated analogues are significantly larger by factors of 10 to 30 going from methyl-ethyl-propyl substituted alkyl vinyl ethers.…”

Products and mechanism of the OH-initiated photo-oxidation of perfluoro ethyl vinyl ether, C2F5OCFCF2

“…Computational studies on reaction of OH with PMVE 18 and perfluoro propyl vinyl ether (C 3 F 7 OCFQCF 2 , PPVE), 15 indicate that addition to the terminal C-atom (R1a) dominates. The large experimental yield of FC(O)C(O)F is not commensurate with a significant contribution of (R1b) and we conclude that the OH-addition is predominantly at the terminal carbon atom (R1a).…”

Gas Phase OH Radical Reaction with 2‐Chloroethyl Vinyl Ether in the 256–333 K Temperature Range: A Combined LP‐LIF and Computational Study

“…This allows the transfer of negative charge from the O atom to the olefinic linkage by p‐π conjugation, which adds extra stability to a molecule. The reaction of alkyl vinyl ethers with OH radical is well studied experimentally as well as theoretically by various groups. In these molecules, apart from the OH radical addition to C=C bond, H‐abstraction by OH radical is also operative at normal temperature and hence the rate coefficient is comparatively higher than corresponding simple ethers.…”