Tetrafluoroethylene

Tetrafluoroethylene (TFE) is a fluorocarbon with the chemical formula C2F4. It is the simplest perfluorinated alkene. This gaseous species is used primarily in the industrial preparation of polymers.

Properties
Tetrafluoroethylene is a colorless, odorless gas. Like all unsaturated fluorocarbons, it is susceptible to nucleophilic attack. It is unstable towards decomposition to C and  and prone to form explosive peroxides in contact with air.

Industrial use
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.

Manufacture
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

Alternatively, it can be prepared by pyrolysis of fluoroform:
2 CHF3 → C2F4 + 2 HF

Laboratory methods
The reverse polymerization reaction – vacuum pyrolysis of PTFE at  in a quartz vessel – is a convenient laboratory synthesis of TFE. The PTFE polymer cracks, and at a pressure below  exclusively C2F4 is obtained. At higher pressures the product mixture contains hexafluoropropylene and octafluorocyclobutane.

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, the detonation of which is usually sufficient to trigger explosive decomposition of TFE to C and CF4. Explosions can also be caused by adiabatic compression If pressurized TFE is allowed into a vessel/pipework at a lower pressure as the atmosphere in the vessel is compressed by the TFE, it may become hot enough to detonate it. This has been known to cause explosions. 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.

See also
Tetrachloroethylene
1,1,1,2-Tetrafluoroethane

References

External links
National Toxicology Program Chemical Repository
Tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride terpolymer -- aka THV, melt-processable members of the fluorocarbon family
 

Category:Organofluorides
Category:Monomers
Category:IARC Group 2A carcinogens