Tetrafluoroethylene

Chembox new
Name = Tetrafluoroethylene
ImageFileL1 = Tetrafluoroethylene.png ImageSizeL1 = 100px
ImageNameL1 = Tetrafluoroethylene
ImageFileR1 = Tetrafluoroethylene3D.png ImageSizeR1 = 100px
ImageNameR1 = Tetrafluoroethylene
IUPACName = tetrafluoroethene
OtherNames = perfluoroethylene
TFE
Section1 = Chembox Identifiers
CASNo = 116-14-3
SMILES = FC(F)=C(F)F
Section2 = Chembox Properties
Formula = C₂F_{4
MolarMass = 100.02 g/mol
Density = 1.519 g/cm³ at -76 °C
MeltingPt = -142.5 °C
BoilingPt = -76.3 °C}

Tetrafluoroethylene (TFE) is a chemical compound with the formula C₂F₄. It is the simplest unsaturated perfluorocarbon. This gaseous species is used primarily in the industrial preparation of polymers. In organic chemistry, tetrafluoroethylene is a potent dienophile.

Properties

Tetrafluoroethylene is a colourless, odourless gas. Like all unsaturated fluorocarbons it is susceptible to nucleophilic attack. It is unstable towards decomposition to C and CF₄ and prone to form explosive peroxides in contact with air. [US Patent 5,345,013, issued to du Pont de Nemours]

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 TFE, but usually not at greater than 50% by weight.

Manufacture

TFE is manufactured from chloroform. [cite journal |abstract= [http://www.bepress.com/ijcre/vol2/A6/] |author=Dae Jin Sung, Dong Ju Moon, Yong Jun Lee, Suk-In Hong |title=Catalytic Pyrolysis of Difluorochloromethane to Produce Tetrafluoroethylene |journal=International Journal of Chemical Reactor Engineering |year=2004 |volume=2 |pages=A6 ] Chloroform is fluorinated by reaction with hydrogen fluoride to produce chlorodifluoromethane (R-22). Pyrolysis of chlorodifluoromethane then yields TFE, with difluorocarbene as an intermediate.:CHCl₃ + 2 HF → CHClF₂ + 2 HCl:2 CHClF₂ → C₂F₄ + 2 HCl

The reverse reaction – vacuum pyrolysis of PTFE at 600–650 °C in a quartz vessel – is a convenient laboratory synthesis of TFE. The PTFE polymer cracks, and at a pressure below 5 torr exclusively C₂F₄ is obtained. At higher pressures the product mixture contains hexafluoropropylene and octafluorocyclobutane. [Hunadi, R. J.; Baum, K. “Tetrafluoroethylene: A Convenient Laboratory Preparation Synthesis 1982, page 454.]

afety

TFE is an alkylating agent, albeit a weak one, and as such is expected to be carcinogenic. LD₅₀(rat, inhalation) = 40000 ppm. [ [http://ntp-server.niehs.nih.gov/ntp/roc/eleventh/profiles/s170tfe.pdf#search=%22tetrafluoroethylene%22 NIH Substance Profile for TFE] ] . 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 scrupulously excluded when handling the compound, 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 pressurised TFE is allowed into a vessel/pipework at a lower pressure the heat generated from compression may be sufficient to ignite the TFE, causing explosion/explosive decomposition.

In industry pipework is flushed with pressurised nitrogen, before the introduction of TFE, both to exclude oxygen and to avoid adiabatic compression.

ee also

*Tetrachloroethylene
*1,1,1,2-Tetrafluoroethane

References

External links

* [http://www.mindfully.org/Plastic/Teflon/Tetrafluoroethylene-NTP-Data.htm National Toxicology Program Chemical Repository]
* [http://www.zeusinc.com/pdf/Zeus_Introduction_to_THV.pdf Tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride terpolymer -- aka THV, melt-processable members of the fluorocarbon family]