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Higher alkanes refer to alkanes with a high number of carbon atoms. There does not exist a formal definition for when an alkane is classified as a 'higher alkane', but one definition distinguishes the higher alkanes as the n-alkanes that are solid under room temperature.

Synthesis

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Higher alkanes are naturally present in crude oil and can be obtained via fractional distillation. Saturated fatty acids decarboxylate to higher alkanes. Long olefins can be hydrogenated to yield higher alkanes. n-alkanes can be isolated via the formation of urea clathrates.They can also be synthesized through Kolbe electrolysis or other coupling reactions like the Wurtz reaction.

Uses

Alkanes from nonane to hexadecane (those alkanes with nine to sixteen carbon atoms) are liquids of higher viscosity, which are less suitable for use in gasoline. They form instead the major part of diesel, kerosene, and aviation fuel. Diesel fuels are characterised by their cetane number, cetane being an older name for hexadecane. However the higher melting points of these alkanes can cause problems at low temperatures and in polar regions, where the fuel becomes too thick to flow correctly. Mixtures of the normal alkanes are used as boiling point standards for simulated distillation by gas chromatography.

Alkanes from hexadecane upwards form the most important components of fuel oil and lubricating oil. In latter function they work at the same time as anti-corrosive agents, as their hydrophobic nature means that water cannot reach the metal surface. Many solid alkanes find use as paraffin wax, used for lubrication, electrical insulation, and candles. Paraffin wax should not be confused with beeswax, which consists primarily of esters.

Alkanes with a chain length of approximately 35 or more carbon atoms are found in bitumen (asphalt), used (for example) in road surfacing. However, the higher alkanes have little value and are usually split into lower alkanes by cracking.

Names

Some alkanes have non-IUPAC trivial names:

• cetane, for hexadecane
• cerane, for hexacosane

Properties

Nonane is the lightest alkane to have a flash point above 25 °C, and is classified as flammable under the US National Library of Medicine.

The properties listed here refer to the straight-chain alkanes (or: n-alkanes).

Nonane to hexadecane

This group of n-alkanes is generally liquid under standard conditions.

Heptadecane to tetracosane

From this group on, the n-alkanes are generally solid at standard conditions.

Pentacosane to triacontane

Hentriacontane to hexatriacontane

Heptatriacontane to dotetracontane

Tritetracontane to octatetracontane

Nonatetracontane to tetrapentacontane

Pentapentacontane to hexacontane

See also

• Alkene
• Alkyne
• Cycloalkane
• Hydrocarbon
• Paraffin wax, composed mostly of higher linear alkanes
• Polyethylene, a linear alkane of polymeric length

References

1. ASTM D5399-09, Standard Test Method for Boiling Point Distribution of Hydrocarbon Solvents by Gas Chromatography
2. Donald Mackay, Handbook of Physical-Chemical Properties and Environmental Fate for Organic Chemicals, ISBN 1420044397, p. 206
3. "Nonane". PubChem. 26 October 2024.
4. Karl Griesbaum, Arno Behr, Dieter Biedenkapp, Heinz-Werner Voges, Dorothea Garbe, Christian Paetz, Gerd Collin, Dieter Mayer Hartmut Höke "Hydrocarbons" in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim. doi:10.1002/14356007.a13_227
5. Weast, Robert C., ed. (1982). CRC Handbook of Chemistry and Physics (63rd ed.). Boca Raton, Fl: CRC Press. p. C-561.

External links

• International Chemical Safety Card 1245 (nonane)
• NIOSH Pocket Guide to Chemical Hazards (nonane)
• International Chemical Safety Card 0428 (decane)

• Alkanes