Tetrafluoromethane

Tetrafluoromethane, also known as carbon tetrafluoride, Freon-14 and R 14, is a carbon fluoride (CF₄). It can be considered either a haloalkane, halomethane, perfluorocarbon or an inorganic compound.

At temperature -198 °C, it has monoclinic structure with lattice constants a = 8.597, b = 4.433, c = 8.381 (.10^-1 nm), β = 118.73°^[1].

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Additional physical properties

Chemistry^[2]

Pure tetrafluoromethane was prepared the first time in 1926.

Tetrafluoromethane can be prepared in laboratory by reaction:

SiC + 2 F₂ → CF₄ + Si

or by fluorination of carbon dioxide, carbon monoxide or phosgene with sulfur tetrafluoride. Commercially it is manufactured by aggressive reaction of fluorine with dichlorodifluoromethane or chlorotrifluoromethane. Another way is electrolysis of fluorides MF, MF₂ with carbon electrode.

Tetrafluoromethane, as other fluorinated hydrocarbons, is very stable due to strength of C-F bonds with bonding energy of 515 kJ.mol^-1 (see Environmental effects). Therefore it is inert to acids and hydroxides influence, however, it reacts explosively with alkali metals. Thermal decomposition produces very toxic gases (carbonyl fluoride, carbon monoxide and in presence of water also corrosive hydrogen fluoride.

It is very slightly soluble in water (about 20 mg.l^-1), but miscible with ethanol, ether, benzine.

Uses

Tetrafluoromethane is sometimes used as a low temperature refrigerant. It is used in circuit board manufacture, manufacture of insulating materials and semiconductors. It is used as a gas etchant and dry/plasma etching.

Environmental effects

Tetrafluoromethane is a gas that contributes to the greenhouse effect. It is very stable and lasts a long time in the atmosphere and is a very powerful greenhouse gas. Its atmospheric lifetime is 50,000 years and global warming factor is 6500 (carbon dioxide has a factor of 1). Although structurally similar to chlorofluorocarbons, tetrafluoromethane does not deplete the ozone layer. This is because the depletion is caused by the chlorine atoms in CFCs, which dissociate when struck by UV radiation. Carbon-fluorine bonds are stronger and less likely to dissociate.

Health risks

Inhalation of tetrafluoromethane can cause, according to concentration, headache, nausea, dizziness and damage of cardiovascular system (mainly heart). Long-terming exposure can cause heavy heart damage.

Because of its heavier density, it can fill up ground area and in non-ventilated places can cause asphyxiation.

References

1. ^ F. Brezina, J. Mollin, R. Pastorek, Z. Sindelar. Chemicke tabulky anorganickych sloucenin (Chemical tables of inorganic compounds). SNTL, 1986.
2. ^ N. N. Greenwood, A. Earnshaw. Chemie prvku (Chemistry of the Elements). Informatorium, Prague, 1993.

See also

• Haloalkane
• Halomethane
• Tetrahalomethane
• Fluoromethane
• Difluoromethane
• Fluoroform
• Carbon tetrachloride (Tetrachloromethane)
• Tetrabromomethane
• Carbon tetraiodide (Tetraiodomethane)

• Hexafluoroethane
• Octafluoropropane

• Silicon tetrafluoride