Tetrafluoroethylene

Tetrafluoroethylene
IUPAC name	tetrafluoroethene
Other names	perfluoroethylene TFE
Identifiers
CAS number	116-14-3
SMILES	FC(F)=C(F)F
Properties
Molecular formula	C2F4
Molar mass	100.02 g/mol
Density	1.519 g/cm³ at -76 °C
Melting point	-142.5 °C
Boiling point	-76.3 °C
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox references

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.

[edit] 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. ^[1]

[edit] 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.

[edit] Manufacture

TFE is manufactured from chloroform.^[2] 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. ^[3]

[edit] Safety

TFE is an alkylating agent, albeit a weak one, and as such is expected to be carcinogenic. LD₅₀(rat, inhalation) = 40000 ppm.^[4]. 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.

[edit] See also

• Tetrachloroethylene
• 1,1,1,2-Tetrafluoroethane

[edit] References

[edit] External links

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