Pentane
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| Names | |||
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| IUPAC name
Pentane
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| Identifiers | |||
3D model (JSmol)
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| 969132 | |||
| ChEBI | |||
| ChEMBL | |||
| ChemSpider | |||
| DrugBank | |||
| ECHA InfoCard | 100.003.358 | ||
| EC Number |
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| 1766 | |||
| MeSH | pentane | ||
PubChem CID
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| RTECS number |
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| UNII | |||
| UN number | 1265 | ||
CompTox Dashboard (EPA)
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| Properties[2] | |||
| C5H12 | |||
| Molar mass | 72.151 g·mol−1 | ||
| Appearance | Colourless liquid | ||
| Odor | Gasoline-like[1] | ||
| Density | 0.626 g mL−1 | ||
| 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) | |||
| log P | 3.255 | ||
| Vapor pressure | 57.90 kPa (at 20.0 °C) | ||
Henry's law
constant (kH) |
7.8 nmol Pa−1 kg−1 | ||
| Acidity (pKa) | ~45 | ||
| Basicity (pKb) | ~59 | ||
| UV-vis (λmax) | 200 nm | ||
Refractive index (nD)
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1.358 | ||
| Viscosity | 0.240 cP (at 20 °C) | ||
| Thermochemistry | |||
Heat capacity (C)
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167.19 J K−1 mol−1 | ||
Std molar
entropy (S⦵298) |
263.47 J K−1 mol−1 | ||
Std enthalpy of
formation (ΔfH⦵298) |
−174.1–−172.9 kJ mol−1 | ||
Std enthalpy of
combustion (ΔcH⦵298) |
−3.5095–−3.5085 MJ mol−1 | ||
| Hazards | |||
| GHS labelling: | |||
   
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| Danger | |||
| H225, H304, H336, H411 | |||
| P210, P261, P273, P301+P310, 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) | |||
| Explosive limits | 1.5–7.8%[1] | ||
| Lethal dose or concentration (LD, LC): | |||
LD50 (median dose)
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LC50 (median concentration)
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130,000 mg/m3 (mouse, 30 min) 128,200 ppm (mouse, 37 min) 325,000 mg/m3 (mouse, 2 hr)[3] | ||
| NIOSH (US health exposure limits): | |||
PEL (Permissible)
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TWA 1000 ppm (2950 mg/m3)[1] | ||
REL (Recommended)
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TWA 120 ppm (350 mg/m3) C 610 ppm (1800 mg/m3) [15-minute][1] | ||
IDLH (Immediate danger)
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1500 ppm[1] | ||
| Related compounds | |||
Related alkanes
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| Supplementary data page | |||
| Pentane (data page) | |||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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 being called isopentane (methylbutane) and neopentane (dimethylpropane). Cyclopentane is not an isomer of pentane.
Pentanes are components of some fuels and are employed as specialty solvents in the laboratory. Their properties are very similar to those of butanes and hexanes.
Isomers
| Common name | normal pentane unbranched pentane n-pentane |
isopentane | neopentane |
| IUPAC name | pentane | 2-methylbutane | 2,2-dimethylpropane |
| Molecular diagram |
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| Skeletal diagram |
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| Melting Point (°C)[4] |
−129.8 | −159.9 | −16.6 |
| Boiling Point (°C)[4] |
36.0 | 27.7 | 9.5 |
| Density (g/l)[4] | 621 | 616 | 586 |
Industrial uses
Pentanes are some of the primary blowing agents used in the production of polystyrene foam and other foams. Usually, a mixture of n-, i-, and increasingly cyclopentane is used for this purpose.
Because of its low boiling point, low cost, and relative safety, pentane is used as a working medium in geothermal power stations. It is added into some refrigerant blends as well.
Pentanes are also used as an active ingredient in some pesticides.[5]
Laboratory use
Pentanes are relatively inexpensive and are the most volatile alkanes that are liquid at room temperature, so they are often used in the laboratory as solvents that can be conveniently evaporated. However, because of their nonpolarity and lack of functionality, they can only dissolve non-polar and alkyl-rich compounds. Pentanes are miscible with most common nonpolar solvents such as chlorocarbons, aromatics, and ethers. They are also often used in liquid chromatography.
Physical properties
The boiling points of the pentane isomers range from about 9 to 36 °C. As is the case for other alkanes, the more branched isomers tend to have lower boiling points.
The same trend normally holds for the melting points of alkane isomers, and indeed 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 better solid-state packing assumed to be possible with its tetrahedral molecule; but this explanation has been challenged on account of it having a lower density than the other two isomers.[4]
The branched isomers are more stable (have lower heat of formation and heat of combustion) than normal pentane. The difference is 1.8 kcal/mol for isopentane, and 5 kcal/mol for neopentane.[6]
Rotation about two central single C-C bonds of n-pentane produces four different conformations.[7]
Reactions
Like other alkanes, pentanes are under standard room temperature and conditions largely unreactive - however, with sufficient activation energy (i.e. an open flame), they get readily oxidized to form carbon dioxide and water:
- C5H12 + 8 O2 → 5 CO2 + 6 H2O + heat/ energy
Like other alkanes, pentanes undergo free radical chlorination:
- 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.
References
- ^ a b c d e 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 or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
- ^ a b c d 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
- ^ 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.
{{cite book}}:|last=has generic name (help) - ^ 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.
External links
- International Chemical Safety Card 0534 at ILO.org
- NIOSH Pocket Guide to Chemical Hazards at CDC.gov
- Phytochemical data for pentane at Ars-grin.gov