Tetrafluoroethylene
Chemical compound
From Wikipedia, the free encyclopedia
Tetrafluoroethylene (TFE) is a fluorocarbon with the chemical formula C2F4. It is a colorless gas. Its structure is F2C=CF2. It is used primarily in the industrial preparation of fluoropolymers. It is the simplest perfluorinated alkene.
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| Names | |||
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| Preferred IUPAC name
Tetrafluoroethene | |||
Other names
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| ECHA InfoCard | 100.003.752 | ||
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CompTox Dashboard (EPA) |
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| Properties | |||
| C2F4 | |||
| Molar mass | 100.016 g·mol−1 | ||
| Appearance | Colorless gas | ||
| Odor | Odorless | ||
| Density | 1.519 g/cm3 at −76 °C | ||
| Melting point | −142.5 °C (−224.5 °F; 130.7 K) | ||
| Boiling point | −76.3 °C (−105.3 °F; 196.8 K) | ||
| Hazards | |||
| Occupational safety and health (OHS/OSH): | |||
Main hazards |
Explosive (especially if oxygen is present), possible carcinogen | ||
| NFPA 704 (fire diamond) | |||
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Related compounds |
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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History
Tetrafluoroethylene was first obtained by the French chemist [fr] Camille Chabrié by heating tetrachloroethylene with silver(II) fluoride. It was named "dicarbon tetrafluoride" based on its composition, analogous to "dicarbon tetrachloride" for tetrachloroethylene which it was first made from.[2]
Properties
Tetrafluoroethylene is a synthetic colorless, odorless gas that is insoluble in water. Like all unsaturated fluorocarbons, it is susceptible to nucleophilic attack. It is unstable towards decomposition to carbon and carbon tetrafluoride (CF4) and prone to form explosive peroxides in contact with air.[3][4]
Industrial use
Polymerization of tetrafluoroethylene produces fluoropolymers such as Teflon and Fluon.[5] PTFE is one of the two fluorocarbon resins composed wholly of fluorine and carbon. The other resin composed purely of carbon and fluorine is the copolymer of TFE with typically 6–9% hexafluoropropene (HFP), which is known as FEP (fluorinated ethylene propylene copolymer). TFE is also used in the preparation of numerous copolymers that also include hydrogen and/or oxygen, including both fluoroplastics and fluoroelastomers. Typical TFE-based fluoroplastics include ETFE, the alternating 1:1 copolymer with ethylene, and PFA, which is a random copolymer similar to FEP but with a minor amount of a perfluoroalkyl vinyl ether (PAVE) rather than HFP. DuPont uses primarily perfluoro(methylvinylether), whereas Daikin uses primarily perfluoro(propylvinylether) in manufacturing PFA. There are numerous other fluoropolymers that contain TFE, but usually not at greater than 50% by weight.
Manufacture
TFE is manufactured from chloroform.[6] Chloroform is fluorinated by reaction with hydrogen fluoride to produce chlorodifluoromethane (R-22). Pyrolysis of chlorodifluoromethane (at 550–750 °C) yields TFE, with difluorocarbene as an intermediate.
Alternatively, it can be prepared by pyrolysis of fluoroform, which is also produced from chloroform and HF:
- 2 CHF3 → C2F4 + 2 HF
Laboratory methods
A convenient, safe method for generating TFE is the pyrolysis of the sodium salt of pentafluoropropionic acid:[7]
The depolymerization reaction – vacuum pyrolysis of PTFE at 650–700 °C (1,200–1,290 °F) in a quartz vessel – is a traditional laboratory synthesis of TFE. The process is however challenging because attention must be paid to pressure, as well as the avoidance of perfluoroisobutene. PTFE polymer cracks, and at a pressure below 5 Torr (670 Pa) exclusively C2F4 is obtained. At higher pressures the product mixture contains hexafluoropropylene and octafluorocyclobutane.[8]
Reactions
Tetrafluoroethylene is a reactive molecule that participates in myriad reactions. Owing to the presence of four fluorine substituents, its reactions differ strongly from the behavior of conventional alkenes such as ethylene. Tetrafluoroethylene dimerizes, giving octafluorocyclobutane. Even normal alkenes and dienes add tetrafluoroethylene in a [2+2] manner. 1,3-Butadiene gives 3-vinyl-1,1,2,2-tetrafluorocyclobutane.[9]
Safety
The main hazard associated with TFE is that of explosion, especially if oxygen is present. TFE reacts with oxygen at low temperatures to form an explosive oxide,[3] the detonation of which is usually sufficient to trigger explosive decomposition of TFE to C and CF4.[10] Explosions can also be caused by adiabatic compression if the TFE is handled under high pressure, which it typically is in an industrial setting. If pressurised TFE is allowed into a vessel or pipework at a lower pressure, then the atmosphere in the vessel will be compressed by the TFE, causing it to heat up, potentially to the point where it might detonate the TFE. This has been known to cause explosions.[11] In industry, pipework is flushed with pressurized nitrogen, before the introduction of TFE, both to exclude oxygen and prevent adiabatic compression.
TFE is an alkylating agent, albeit a weak one, and as such is expected to be a carcinogen. LD50(rat, inhalation) = 40000 ppm.[12]
The International Agency for Research on Cancer classifies TFE as probably carcinogenic to humans based on animal studies.[13] TFE is not considered to be a PFAS[14]