Pentane is an organic compound with the formula C5H12—that is, an alkane with five carbon atoms. The term may refer to any of three structural isomers, or to a mixture of them: in the IUPAC nomenclature, however, pentane means exclusively the n-pentane isomer; the other two are called isopentane (methylbutane) and neopentane (dimethylpropane). Cyclopentane is not an isomer of pentane because it has only 10 hydrogen atoms where pentane has 12.
|Preferred IUPAC name
3D model (JSmol)
CompTox Dashboard (EPA)
|Molar mass||72.151 g·mol−1|
|Density||0.626 g mL−1; 0.6262 g mL−1 (at 20 °C)|
|Melting point||−130.5 to −129.1 °C; −202.8 to −200.3 °F; 142.7 to 144.1 K|
|Boiling point||35.9 to 36.3 °C; 96.5 to 97.3 °F; 309.0 to 309.4 K|
|40 mg L−1 (at 20 °C)|
|Vapor pressure||57.90 kPa (at 20.0 °C)|
|7.8 nmol Pa−1 kg−1|
|UV-vis (λmax)||200 nm|
Refractive index (nD)
|Viscosity||0.240 mPa·s (at 20 °C)|
Heat capacity (C)
|167.19 J K−1 mol−1|
|263.47 J K−1 mol−1|
Std enthalpy of
|−174.1–−172.9 kJ mol−1|
Std enthalpy of
|−3.5095–−3.5085 MJ mol−1|
|Safety data sheet||See: data page|
|GHS Signal word||Danger|
|H225, H304, H336, H411|
|P210, P261, P273, P301+310, P331|
|NFPA 704 (fire diamond)|
|Flash point||−49.0 °C (−56.2 °F; 224.2 K)|
|260.0 °C (500.0 °F; 533.1 K)|
|Lethal dose or concentration (LD, LC):|
LD50 (median dose)
LC50 (median concentration)
|130,000 mg/m3 (mouse, 30 min)|
128,200 ppm (mouse, 37 min)
325,000 mg/m3 (mouse, 2 hr)
|NIOSH (US health exposure limits):|
|TWA 1000 ppm (2950 mg/m3)|
|TWA 120 ppm (350 mg/m3) C 610 ppm (1800 mg/m3) [15-minute]|
IDLH (Immediate danger)
|Supplementary data page|
|Refractive index (n),|
Dielectric constant (εr), etc.
|UV, IR, NMR, MS|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
Acid-catalyzed isomerization gives isopentane, which is used in producing high-octane fuels.
Because of their low boiling points, low cost, and relative safety, pentanes are used as a working medium in geothermal power stations in some blended refrigerants also used as a working medium in organic rankine cycles.
Pentanes are relatively inexpensive and are the most volatile liquid alkanes at room temperature, so they are often used in the laboratory as solvents that can be conveniently and rapidly evaporated. However, because of their nonpolarity and lack of functionality, they dissolve only nonpolar and alkyl-rich compounds. Pentanes are miscible with most common nonpolar solvents such as chlorocarbons, aromatics, and ethers.
They are often used in liquid chromatography.
The boiling points of the pentane isomers range from about 9 to 36 °C. As is the case for other alkanes, the more thickly branched isomers tend to have lower boiling points.
The same tends to be true for the melting points of alkane isomers, and that of isopentane is 30 °C lower than that of n-pentane. However, the melting point of neopentane, the most heavily branched of the three, is 100 °C higher than that of isopentane. The anomalously high melting point of neopentane has been attributed to the tetrahedral molecules packing more closely in solid form. But this explanation is contradicted by the fact that neopentane has a lower density than the other two isomers, and the high melting point is actually caused by neopentane’s significantly lower entropy of fusion.
Reactions and occurrenceEdit
Like other alkanes, pentanes are largely unreactive at standard room temperature and conditions - however, with sufficient activation energy (e.g., an open flame), they readily oxidize to form carbon dioxide and water:
- C5H12 + 8 O2 → 5 CO2 + 6 H2O + heat/energy
- C5H12 + Cl2 → C5H11Cl + HCl
Such reactions are unselective; with n-pentane, the result is a mixture of the 1-, 2-, and 3-chloropentanes, as well as more highly chlorinated derivatives. Other radical halogenations can also occur.
Pentane is a component of exhaled breath for some individuals. A degradation product of unsaturated fatty acids, its presence is associated with certain diseases and cancers.
- Hofmann, August Wilhelm Von (1 January 1867). "I. On the action of trichloride of phosphorus on the salts of the aromatic monamines". Proceedings of the Royal Society of London. 15: 54–62. doi:10.1098/rspl.1866.0018.
- NIOSH Pocket Guide to Chemical Hazards. "#0486". National Institute for Occupational Safety and Health (NIOSH).
- Record of n-Pentane in the GESTIS Substance Database of the Institute for Occupational Safety and Health, accessed on 19 April 2011.
- "n-Pentane". Immediately Dangerous to Life and Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
- Karl Griesbaum, Arno Behr, Dieter Biedenkapp, Heinz-Werner Voges, Dorothea Garbe, Christian Paetz, Gerd Collin, Dieter Mayer, Hartmut Höke (2002). "Hydrocarbons". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a13_227. ISBN 978-3527306732.CS1 maint: uses authors parameter (link)
- Milne, ed., G.W.A. (2005). Gardner's Commercially Important Chemicals: Synonyms, Trade Names, and Properties. Hoboken, New Jersey: John Wiley & Sons, Inc. p. 477. ISBN 978-0-471-73518-2.CS1 maint: extra text: authors list (link)
- James Wei (1999), Molecular Symmetry, Rotational Entropy, and Elevated Melting Points. Ind. Eng. Chem. Res., volume 38 issue 12, pp. 5019–5027 doi:10.1021/ie990588m
- From the values listed at Standard enthalpy change of formation (data table).
- Roman M. Balabin (2009). "Enthalpy Difference between Conformations of Normal Alkanes: Raman Spectroscopy Study of n-Pentane and n-Butane". J. Phys. Chem. A. 113 (6): 1012–9. doi:10.1021/jp809639s. PMID 19152252.
- Phillips, Michael; Herrera, Jolanta; Krishnan, Sunithi; Zain, Mooena; Greenberg, Joel; Cataneo, Renee N. (1999). "Variation in volatile organic compounds in the breath of normal humans". Journal of Chromatography B: Biomedical Sciences and Applications. 729 (1–2): 75–88. doi:10.1016/S0378-4347(99)00127-9. PMID 10410929.