Tetrafluoroethylene(Redirected from Tetrafluoroethene)
Tetrafluoroethylene (TFE) is a fluoromonomer with chemical formula C2F4. It belongs to the family of fluorocarbons and is the simplest perfluorinated alkene. This gaseous species is used primarily in the industrial preparation of polymers.
3D model (JSmol)
|Molar mass||100.02 g/mol|
|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)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Tetrafluoroethylene is a colorless, odorless gas. Like all unsaturated fluorocarbons it is susceptible to nucleophilic attack. It is unstable towards decomposition to C and CF
4 and prone to form explosive peroxides in contact with air.
Polymerization of tetrafluoroethylene produces polytetrafluoroethylene (PTFE) polymers such as Teflon and Fluon. 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 tetrafluoroethylene, but usually not at greater than 50% by weight.
TFE is manufactured from chloroform. 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.
- CHCl3 + 2 HF → CHClF2 + 2 HCl
- 2 CHClF2 → C2F4 + 2 HCl
The reverse polymerization reaction – vacuum pyrolysis of PTFE at 650–700 °C (1,200–1,290 °F) in a quartz vessel – is a convenient laboratory synthesis of TFE. The 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.
TFE is an alkylating agent, albeit a weak one, and as such is expected to be carcinogenic. LD50(rat, inhalation) = 40000 ppm. The compound is best handled diluted with an inert gas, as localized heating can provoke explosive decomposition to C and CF4. When working with TFE, oxygen must be carefully excluded, as it catalyzes autopolymerization, which can take place with great force.
There is also a danger of explosion when working with TFE, from adiabatic compression. If pressurized TFE is allowed into a vessel/pipework at a lower pressure the heat generated from compression may be sufficient to trigger the TFE explosive decomposition.
In industry, pipework is flushed with pressurized nitrogen, before the introduction of TFE, both to exclude oxygen and to avoid adiabatic compression .
- U.S. Patent 5,345,013 issued to du Pont de Nemours
- Dae Jin Sung; Dong Ju Moon; Yong Jun Lee; Suk-In Hong (2004). "Catalytic Pyrolysis of Difluorochloromethane to Produce Tetrafluoroethylene". International Journal of Chemical Reactor Engineering. 2: A6. doi:10.2202/1542-6580.1065.
- R. J. Hunadi & K. Baum (1982). "Tetrafluoroethylene: A Convenient Laboratory Preparation". Synthesis. 39: 454. doi:10.1055/s-1982-29830.
- NIH Substance Profile for TFE
- "The Explosive Decomposition of Tetrafluoroethylene: Large Scale Tests and Simulations | Request PDF". ResearchGate. Retrieved 2018-11-01.
- National Toxicology Program Chemical Repository
- Tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride terpolymer -- aka THV, melt-processable members of the fluorocarbon family
- Sleeuwenhoek, Anne; Cherrie, John (2012). "Exposure assessment of tetrafluoroethylene and ammonium perfluorooctanoate 1951-2002". Journal of Environmental Monitoring.