Chemistry of 1,1,2,3,3,4,4-Heptafluorobut-1-ene Initiated by Chlorine Atoms
Abstract
Unsaturated hydroflurocarbons (HFCs) are potential substitutes for long-lived saturated HFCs with high global warming potentials (GWP). Here we evaluate some properties of CF2H-CF2-CF=CF2 (HFB) at room temperature. Photolysis of Cl2 by a mercury lamp generated atomic Cl which reacted with a mixture of ethane and HFB diluted in about 1 bar of artificial air. Reactants and products were monitored via FT-IR spectroscopy and the rate coefficient was determined via relative rate methods. COF2 was identified as a product and its yield was determined to be close to 1.
Plausible second products are CF2H-CF2-CFO, 2,2,3,3-tetrafluoropropanoyl fluoride (TPF), and CF2Cl-CFO. The observed IR spectrum was matched to the first compound via density functional theory and anharmonic frequency calculations. These showed the importance of considering an equilibrium distribution of all conformers created by rotations around single bonds, in order to make a quantitative comparison. No evidence for C-Cl bonding was seen in the IR, nor the extra COF2 that would be a co-product. Absolute IR cross-sections for TPF were obtained which allow the assessment of its radiative efficiency (RE). Likewise, the first IR cross-sections and RE of HPF were obtained. In order to match them computationally, again an equilibrium mixture of rotational conformers was considered. Possible reasons for the lack of formation of significant quantities of CF2Cl-CFO are either kinetic control over which end of the π bond in HFB is preferentially attacked by atomic Cl, or variations in the bond strengths in the intermediates that determine which fragmentation is favored.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMA185.0009M
- Keywords:
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- 0317 Chemical kinetic and photochemical properties;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0340 Middle atmosphere: composition and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0365 Troposphere: composition and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0394 Instruments and techniques;
- ATMOSPHERIC COMPOSITION AND STRUCTURE