Tetrafluoromethane, also known as carbon tetrafluoride or R-14, is the simplest perfluorocarbon (CF4). As its IUPAC name indicates, tetrafluoromethane is the perfluorinated counterpart to the hydrocarbon methane. It can also be classified as a haloalkane or halomethane. Tetrafluoromethane is a useful refrigerant but also a potent greenhouse gas.[4] It has a very high bond strength due to the nature of the carbon–fluorine bond.
Bonding
Because of the multiple carbon–fluorine bonds, and the high electronegativity of fluorine, the carbon in tetrafluoromethane has a significant positive partial charge which strengthens and shortens the four carbon–fluorine bonds by providing additional ionic character. Carbon–fluorine bonds are the strongest single bonds in organic chemistry.[5] Additionally, they strengthen as more carbon–fluorine bonds are added to the same carbon. In the one-carbon organofluorine compounds represented by molecules of fluoromethane, difluoromethane, trifluoromethane, and tetrafluoromethane, the carbon–fluorine bonds are strongest in tetrafluoromethane.[6] This effect is due to the increased coulombic attractions between the fluorine atoms and the carbon because the carbon has a positive partial charge of 0.76.[6]
Although it can be made from a myriad of precursors and fluorine, elemental fluorine is expensive and difficult to handle. Consequently, CF 4 is prepared on an industrial scale using hydrogen fluoride:[4]
Tetrafluoromethane, like other fluorocarbons, is very stable due to the strength of its carbon–fluorine bonds. The bonds in tetrafluoromethane have a bonding energy of 515 kJ⋅mol−1. As a result, it is inert to acids and hydroxides. However, it reacts explosively with alkali metals. Thermal decomposition or combustion of CF4 produces toxic gases (carbonyl fluoride and carbon monoxide) and in the presence of water will also yield hydrogen fluoride.
It is very slightly soluble in water (about 20 mg⋅L−1), but miscible with organic solvents.
Tetrafluoromethane is the most abundant perfluorocarbon in the atmosphere, where it is designated as PFC-14. Its atmospheric concentration is growing.[11] As of 2019, the man-made gases CFC-11 and CFC-12 continue to contribute a stronger radiative forcing than PFC-14.[12]
Although structurally similar to chlorofluorocarbons (CFCs), tetrafluoromethane does not deplete the ozone layer[13] because the carbon–fluorine bond is much stronger than that between carbon and chlorine.[14]
Main industrial emissions of tetrafluoromethane besides hexafluoroethane are produced during production of aluminium using Hall-Héroult process. CF4 also is produced as product of the breakdown of more complex compounds such as halocarbons.[15]
Health risks
Due to its density, tetrafluoromethane can displace air, creating an asphyxiation hazard in inadequately ventilated areas. Otherwise, it is normally harmless due to its stability.
^Lide, David R.; Kehiaian, Henry V. (1994). CRC Handbook of Thermophysical and Themochemical Data (PDF). CRC Press. p. 31.
^Abjean, R.; A. Bideau-Mehu; Y. Guern (15 July 1990). "Refractive index of carbon tetrafluoride (CF4) in the 300-140 nm wavelength range". Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 292 (3): 593–594. Bibcode:1990NIMPA.292..593A. doi:10.1016/0168-9002(90)90178-9.
^Kestin, J.; Ro, S.T.; Wakeham, W.A. (1971). "Reference values of the viscosity of twelve gases at 25°C". Transactions of the Faraday Society. 67: 2308–2313. doi:10.1039/TF9716702308.
^ a bSiegemund, Günter; Schwertfeger, Werner; Feiring, Andrew; Smart, Bruce; Behr, Fred; Vogel, Herward; McKusick, Blaine (2002). "Fluorine Compounds, Organic". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a11_349. ISBN 978-3527306732.
^O'Hagan D (February 2008). "Understanding organofluorine chemistry and in cations. An introduction to the C–F bond". Chemical Society Reviews. 37 (2): 308–19. doi:10.1039/b711844a. PMID 18197347.
^ a bLemal, D.M. (2004). "Perspective on Fluorocarbon Chemistry". J. Org. Chem.69 (1): 1–11. doi:10.1021/jo0302556. PMID 14703372.
^K. Williams, K. Gupta, M. Wasilik. Etch Rates for Micromachining Processing – Part II J. Microelectromech. Syst., vol. 12, pp. 761–777, December 2003.
^Moon, Myung-Kook; Nam, Uk-Won; Lee, Chang-Hee; Em, V.T.; Choi, Young-Hyun; Cheon, Jong-Kyu; Kong, Kyung-Nam (2005). "Low efficiency 2-dimensional position-sensitive neutron detector for beam profile measurement". Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 538 (1–3): 592–596. Bibcode:2005NIMPA.538..592M. doi:10.1016/j.nima.2004.09.020.
^Artaxo, Paulo; Berntsen, Terje; Betts, Richard; Fahey, David W.; Haywood, James; Lean, Judith; Lowe, David C.; Myhre, Gunnar; Nganga, John; Prinn, Ronald; Raga, Graciela; Schulz, Michael; van Dorland, Robert (February 2018). "Changes in Atmospheric Constituents and in Radiative Forcing" (PDF). Intergovernmental Panel on Climate Change. p. 212. Retrieved 17 March 2021.
^Jubb, Aaron M.; McGillen, Max R.; Portmann, Robert W.; Daniel, John S.; Burkholder, James B. (2015). "An atmospheric photochemical source of the persistent greenhouse gas CF4". Geophysical Research Letters. 42 (21): 9505–9511. Bibcode:2015GeoRL..42.9505J. doi:10.1002/2015GL066193. ISSN 0094-8276.
External links
International Chemical Safety Card 0575
National Pollutant Inventory – Fluoride and compounds fact sheet
Data from Air Liquide Archived 2011-07-21 at the Wayback Machine
Vapor pressure graph at Air Liquide
MSDS at Oxford University
Protocol for measurement of tetrafluoromethane and hexafluoroethane from primary aluminium production