Pentane

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Pentane
Skeletal formula of pentane
Skeletal formula of pentane with all explicit hydrogens added
Ball and stick model of pentane Spacefill model of pentane
Identifiers
CAS number 109-66-0 YesY
PubChem 8003
ChemSpider 7712 YesY
UNII 4FEX897A91 YesY
EC number 203-692-4
UN number 1265
DrugBank DB03119
MeSH pentane
ChEBI CHEBI:37830 YesY
ChEMBL CHEMBL16102 YesY
RTECS number RZ9450000
Beilstein Reference 969132
Gmelin Reference 1766
Jmol-3D images Image 1
Properties[1]
Molecular formula C5H12
Molar mass 72.15 g mol−1
Appearance Colourless liquid
Odor Odourless
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
Solubility in water 40 mg L−1 (at 20 °C)
log P 3.255
Vapor pressure 57.90 kPa (at 20.0 °C)
kH 7.8 nmol Pa−1 kg−1
Acidity (pKa) ~45
Basicity (pKb) ~59
λmax 200 nm
Refractive index (nD) 1.358
Viscosity 0.240 cP (at 20 °C)
Thermochemistry
Specific
heat capacity
C
167.19 J K−1 mol−1
Std molar
entropy
So298
263.47 J K−1 mol−1
Std enthalpy of
formation
ΔfHo298
−174.1–−172.9 kJ mol−1
Std enthalpy of
combustion
ΔcHo298
−3.5095–−3.5085 MJ mol−1
Hazards
MSDS External MSDS
GHS pictograms The flame pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) The exclamation-mark pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) The health hazard pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) The environment pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)
GHS signal word DANGER
GHS hazard statements H225, H304, H336, H411
GHS precautionary statements P210, P261, P273, P301+310, P331
EU Index 601-006-00-1
EU classification Extremely Flammable F+ Harmful Xn Dangerous for the Environment (Nature) N
R-phrases R12, R51/53, R65, R66, R67
S-phrases (S2), S16, S29, S33
NFPA 704
Flammability code 4: Will rapidly or completely vaporize at normal atmospheric pressure and temperature, or is readily dispersed in air and will burn readily. Flash point below 23 °C (73 °F). E.g., propane Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point −49.0 °C (−56.2 °F; 224.2 K)
Explosive limits 1.4–8.3%
LD50
  • 3 g kg−1 (dermal, rabbit)
  • 5 g kg−1 (oral, mouse)
Related compounds
Related alkanes
Supplementary data page
Structure and
properties
n, εr, etc.
Thermodynamic
data
Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

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[edit]

Common name normal pentane
unbranched pentane
n-pentane
isopentane neopentane
IUPAC name pentane 2-methylbutane 2,2-dimethylpropane
Molecular
diagram
N-Pentan.png Isopentane.PNG Neopentane.PNG
Skeletal
diagram
Pentane-2D-Skeletal.svg Isopentane-2D-skeletal.png Neopentane-2D-skeletal.png
Melting
Point (°C)[2]
−129.8 −159.9 −16.6
Boiling
Point (°C)[2]
36.0 27.7 9.5
Density (g/L)[2] 621 616 586

Industrial uses[edit]

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.[3]

Laboratory use[edit]

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[edit]

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 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.[2]

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.[4]

Rotation about two central single C-C bonds of n-pentane produces four different conformations.[5]

Reactions[edit]

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

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[edit]

  1. ^ Record of n-Pentane in the GESTIS Substance Database from the IFA, accessed on 19 April 2011
  2. ^ 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
  3. ^ 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. 
  4. ^ From the values listed at Standard enthalpy change of formation (data table).
  5. ^ 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[edit]