Tetrafluoroethylene

Tetrafluoroethylene (TFE) is a chemical compound composed containing only carbon and fluorine with the molecular formula C₂F₄. This gaseous species is used primarily in the industrial preparation of polymers. In organic chemistry, tetrafluoroethylene is a potent dienophile.

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Properties

TFE is a derivative of ethylene in which each of the four hydrogen atoms have been replaced with fluorine. Tetrafluoroethylene is a colourless, odourless gas. Like all unsaturated fluorocarbons it is susceptible to nucleophilic attack. In air it is prone to form explosive peroxides.^{[citation needed]}

Industrial use

Polymerization of tetrafluoroethylene produces polytetrafluoroethylene (PTFE) polymers such as Teflon. 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.^[1] Chloroform is fluorinated by reaction with hydrogen fluoride to produce chlorodifluoromethane (R-22). Pyrolysis of chlorodifluoromethane then yields TFE.

CHCl₃ + 2 HF → CHClF₂ + 2 HCl

2 CHClF₂ → C₂F₄ + 2 HCl

A laboratory synthesis entails pyrolysis of a PTFE under a vacuum. The PTFE polymer "cracks" and depending on the pressure, produces mainly C₂F₄.^[2]

Safety

LD₅₀(rat, inhalation) = 40000 ppm.^[3]

See also

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

References

1. ^ 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.
2. ^ Hunadi, R. J.; Baum, K. “Tetrafluoroethylene: A Convenient Laboratory Preparation Synthesis 1982, page 454.
3. ^ NIH Substance Profile for TFE