Tetrafluoromethane

Chembox new
ImageFileL1 = Carbon-tetrafluoride-2D-dimensions.png ImageSizeL1 = 150
ImageFileR1 = Carbon-tetrafluoride-3D-balls-B.png ImageSizeR1 = 110px
IUPACName = Tetrafluoromethane Carbon tetrafluoride
OtherNames = Perfluoromethane, Tetrafluorocarbon, Freon 14, Halon 14, Arcton 0, CFC 14, PFC 14, R 14, UN 1982
Section1 = Chembox Identifiers
CASNo = 75-73-0
EINECS = 200-896-5
PubChem = 6393
SMILES = C(F)(F)(F)F
InChI = 1/CF4/c2-1(3,4)5
RTECS = FG4920000
Section2 = Chembox Properties
Formula = CF₄
MolarMass = 88.00 g/mol
Appearance = Colorless odorless gas
Density = 3.72 g/l, gas (15 °C)
MeltingPt = -183.6 °C (89.6 K)
BoilingPt = -127.8 °C (145.4 K)
Solubility = 0.005 %_V at 20 °C0.0038 %_V at 25 °C
VaporPressure = 3.65 MPa at 15 °C106.5 kPa at -127 °C
Section3 = Chembox Structure
CrystalStruct =
Coordination =
MolShape = Tetrahedral
Section3 = Chembox Hazards
MainHazards =
RPhrases = None
SPhrases = None
NFPA-H = 1
NFPA-F = 0
NFPA-R = 0
NFPA-O =
FlashPt = Non flammable
Autoignition = > 1100 °C

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 a temperature of −198 °C, it has monoclinic structure with lattice constants "a" = 8.597, "b" = 4.433, "c" = 8.381 (.10^-1 nm), β = 118.73°F. Brezina, J. Mollin, R. Pastorek, Z. Sindelar. "Chemicke tabulky anorganickych sloucenin" ("Chemical tables of inorganic compounds"). SNTL, 1986.] .

Additional physical properties

Chemistry

Pure tetrafluoromethane was first synthesised in 1926Greenwood&Earnshaw] .

Tetrafluoromethane can be prepared in the laboratory by the reaction of silicon carbide with fluorine:: SiC + 2 F₂ → CF₄ + Sior by the fluorination of carbon dioxide, carbon monoxide or phosgene with sulfur tetrafluoride. Commercially it is manufactured by the aggressive reaction of fluorine with dichlorodifluoromethane or chlorotrifluoromethane; it is also produced during the electrolysis of metal fluorides MF, MF₂ using a carbon electrode.

Tetrafluoromethane, as other fluorinated hydrocarbons, is very stable due to the strength of C-F bonds with bonding energy of 515 kJ.mol^-1 (see Environmental effects). As a result, it is inert to acids and hydroxides. However, it reacts explosively with alkali metals. Thermal decomposition of CF₄produces toxic gases (carbonyl fluoride and carbon monoxide) and in the presence of water will also yield hydrogen fluoride.

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

Uses

Tetrafluoromethane is sometimes used as a low temperature refrigerant. It is used in electronics microfabrication alone or in combination with oxygen as a plasma etchant for silicon, silicon dioxide, and silicon nitride.K. Williams, K. Gupta, M. Wasilik. "Etch Rates for Micromachining Processing - Part II" J. Microelectromech. Syst., vol. 12, pp. 761-777, Dec. 2003.]

Environmental effects

Tetrafluoromethane is a potent greenhouse gas that contributes to the greenhouse effect. It is very stable, has an atmospheric lifespan of 50,000 years, and a high greenhouse warming potential of 6500 (CO₂ has a factor of 1); however, the low amount in the atmosphere restricts the overall radiative forcing effect.fact|date=July 2008

Although structurally similar to chlorofluorocarbons (CFCs), 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.fact|date=July 2008

Health risks

Inhalation of tetrafluoromethane can cause, depending on concentration, headache, nausea, dizziness and damage to the cardiovascular system (mainly the heart). Long-term exposure can cause severe heart damage.

Due to its density, tetrafluoromethane can displace air, creating an asphyxiation hazard in inadequately ventilated areas.

References

See also

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

* Hexafluoroethane
* Octafluoropropane

* Silicon tetrafluoride

External links

*ICSC|0575|05
* [http://www.npi.gov.au/database/substance-info/profiles/44.html National Pollutant Inventory - Flouride and compounds fact sheet]
* [http://encyclopedia.airliquide.com/Encyclopedia.asp?GasID=61 Data from Air Liquide]
* [http://encyclopedia.airliquide.com/images_encyclopedie/VaporPressureGraph/Tetrafluoromethane_Vapor_Pressure.gifVapor pressure graph at Air Liquide]
* [http://ptcl.chem.ox.ac.uk/MSDS/CA/carbon_tetrafluoride.html MSDS at Oxford University]
* [http://www.climatevision.gov/sectors/aluminum/pdfs/tms_protocol.pdf Protocol for measurement of tetrafluoromethane and hexafluoroethane from primary aluminium production]
* [http://www.cheric.org/kdb/kdb/hcprop/listcmp.php?cmpclass=48 Chemical and physical properties table]