Mechanistic study of the reaction of CH 2 F 2 with Cl atoms in the absence and presence of CH 4 or C 2 H 6 : Decomposition of CHF 2 OH and fate of the CHF 2 O radical
(2019) In Physical Chemistry Chemical Physics 21(18). p.9376-9383- Abstract
To assess the atmospheric fate of fluorinated compounds, chamber experiments were performed with Fourier transform infrared spectroscopy investigating the products of difluoromethane, CH 2 F 2 , at 296 ± 2 K. The reactions were initiated by reaction of CH 2 F 2 with Cl atoms in the absence and presence of CH 4 or C 2 ... (More)
To assess the atmospheric fate of fluorinated compounds, chamber experiments were performed with Fourier transform infrared spectroscopy investigating the products of difluoromethane, CH 2 F 2 , at 296 ± 2 K. The reactions were initiated by reaction of CH 2 F 2 with Cl atoms in the absence and presence of CH 4 or C 2 H 6 in air or O 2 . No evidence of formation of the fluorinated alcohol, CHF 2 OH, from the reactions of the CHF 2 O 2 radical with either CH 3 O 2 or CH 3 CH 2 O 2 was observed. However, evidence of an alkoxy radical pathway was observed to form CHF 2 OH. The alkoxy radical, CHF 2 O, abstracts a hydrogen atom from CH 2 F 2 (with reaction mixtures of high initial CH 2 F 2 concentrations) to give the alcohol CHF 2 OH that in turn decomposes with a rate coefficient of k(CHF 2 OH) = (1.68 × 10 -3 ± 0.19 × 10 -3 ) s -1 , giving a half-life of the alcohol of (412 ± 48) s. Theoretical calculations indicate that the CHF 2 OH decomposition is unlikely to be a unimolecular process, and we instead propose that it is catalyzed by -OH groups present in molecules, or on particles or surfaces. HC(O)F is formed in a yield indistinguishable from 100% from the decomposition of CHF 2 OH. The competition between the reaction of CHF 2 O radicals with O 2 and with CH 2 F 2 was investigated and an experimental rate coefficient ratio of 0.57 ± 0.08 of reaction with O 2 over reaction with CH 2 F 2 was determined. Ab initio calculations support a larger reaction barrier for the O 2 reaction by 0.5 kcal mol -1 , with transition state theory predicting a rate coefficient ratio of 0.35, in reasonable agreement with experiment. The primary product of the atmospheric degradation of CH 2 F 2 is expected to be C(O)F 2 formed by the reaction of CHF 2 O with O 2 .
(Less)
- author
- Østerstrøm, Freja F. ; Andersen, Christina LU and Da Silva, Gabriel
- organization
- publishing date
- 2019
- type
- Contribution to journal
- publication status
- published
- subject
- in
- Physical Chemistry Chemical Physics
- volume
- 21
- issue
- 18
- pages
- 8 pages
- publisher
- Royal Society of Chemistry
- external identifiers
-
- scopus:85065566136
- pmid:30994634
- ISSN
- 1463-9076
- DOI
- 10.1039/c8cp06425c
- language
- English
- LU publication?
- yes
- id
- a37e44a3-358e-45eb-a2b5-1d2ccbf43ba3
- date added to LUP
- 2019-06-04 11:26:23
- date last changed
- 2024-01-16 00:39:46
@article{a37e44a3-358e-45eb-a2b5-1d2ccbf43ba3,
abstract = {{<p> To assess the atmospheric fate of fluorinated compounds, chamber experiments were performed with Fourier transform infrared spectroscopy investigating the products of difluoromethane, CH <sub>2</sub> F <sub>2</sub> , at 296 ± 2 K. The reactions were initiated by reaction of CH <sub>2</sub> F <sub>2</sub> with Cl atoms in the absence and presence of CH <sub>4</sub> or C <sub>2</sub> H <sub>6</sub> in air or O <sub>2</sub> . No evidence of formation of the fluorinated alcohol, CHF <sub>2</sub> OH, from the reactions of the CHF <sub>2</sub> O <sub>2</sub> radical with either CH <sub>3</sub> O <sub>2</sub> or CH <sub>3</sub> CH <sub>2</sub> O <sub>2</sub> was observed. However, evidence of an alkoxy radical pathway was observed to form CHF <sub>2</sub> OH. The alkoxy radical, CHF <sub>2</sub> O, abstracts a hydrogen atom from CH <sub>2</sub> F <sub>2</sub> (with reaction mixtures of high initial CH <sub>2</sub> F <sub>2</sub> concentrations) to give the alcohol CHF <sub>2</sub> OH that in turn decomposes with a rate coefficient of k(CHF <sub>2</sub> OH) = (1.68 × 10 <sup>-3</sup> ± 0.19 × 10 <sup>-3</sup> ) s <sup>-1</sup> , giving a half-life of the alcohol of (412 ± 48) s. Theoretical calculations indicate that the CHF <sub>2</sub> OH decomposition is unlikely to be a unimolecular process, and we instead propose that it is catalyzed by -OH groups present in molecules, or on particles or surfaces. HC(O)F is formed in a yield indistinguishable from 100% from the decomposition of CHF <sub>2</sub> OH. The competition between the reaction of CHF <sub>2</sub> O radicals with O <sub>2</sub> and with CH <sub>2</sub> F <sub>2</sub> was investigated and an experimental rate coefficient ratio of 0.57 ± 0.08 of reaction with O <sub>2</sub> over reaction with CH <sub>2</sub> F <sub>2</sub> was determined. Ab initio calculations support a larger reaction barrier for the O <sub>2</sub> reaction by 0.5 kcal mol <sup>-1</sup> , with transition state theory predicting a rate coefficient ratio of 0.35, in reasonable agreement with experiment. The primary product of the atmospheric degradation of CH <sub>2</sub> F <sub>2</sub> is expected to be C(O)F <sub>2</sub> formed by the reaction of CHF <sub>2</sub> O with O <sub>2</sub> . </p>}},
author = {{Østerstrøm, Freja F. and Andersen, Christina and Da Silva, Gabriel}},
issn = {{1463-9076}},
language = {{eng}},
number = {{18}},
pages = {{9376--9383}},
publisher = {{Royal Society of Chemistry}},
series = {{Physical Chemistry Chemical Physics}},
title = {{Mechanistic study of the reaction of CH <sub>2</sub> F <sub>2</sub> with Cl atoms in the absence and presence of CH <sub>4</sub> or C <sub>2</sub> H <sub>6</sub> : Decomposition of CHF <sub>2</sub> OH and fate of the CHF <sub>2</sub> O radical}},
url = {{http://dx.doi.org/10.1039/c8cp06425c}},
doi = {{10.1039/c8cp06425c}},
volume = {{21}},
year = {{2019}},
}