Pentane

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Pentane
Identifiers
CAS number109-66-0 YesY
PubChem8003
ChemSpider7712 YesY
UNII4FEX897A91 YesY
EC number203-692-4
UN number1265
DrugBankDB03119
MeSHpentane
ChEBICHEBI:37830 YesY
ChEMBLCHEMBL16102 YesY
RTECS numberRZ9450000
Beilstein Reference969132
Gmelin Reference1766
Jmol-3D imagesImage 1
Properties[1]
Molecular formulaC5H12
Molar mass72.15 g mol−1
AppearanceColourless liquid
OdorOdourless
Density0.626 g mL−1
Melting point−130.5 to −129.1 °C; −202.8 to −200.3 °F; 142.7 to 144.1 K
Boiling point35.9 to 36.3 °C; 96.5 to 97.3 °F; 309.0 to 309.4 K
Solubility in water40 mg L−1 (at 20 °C)
log P3.255
Vapor pressure57.90 kPa (at 20.0 °C)
kH7.8 nmol Pa−1 kg−1
Acidity (pKa)~45
Basicity (pKb)~59
λmax200 nm
Refractive index (nD)1.358
Viscosity240 μPa s (at 20 °C)
Thermochemistry
Std enthalpy of
formation
ΔfHo298
−174.1–−172.9 kJ mol−1
Std enthalpy of
combustion
ΔcHo298
−3.5095–−3.5085 MJ mol−1
Standard molar
entropy
So298
263.47 J K−1 mol−1
Specific heat capacity, C167.19 J K−1 mol−1
Hazards
MSDSExternal MSDS
GHS pictogramsThe 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 wordDANGER
GHS hazard statementsH225, H304, H336, H411
GHS precautionary statementsP210, P261, P273, P301+310, P331
EU Index601-006-00-1
EU classificationFlammable F+ Harmful Xn Dangerous for the Environment (Nature) N
R-phrasesR12, R51/53, R65, R66, R67
S-phrases(S2), S16, S29, S33
NFPA 704
NFPA 704.svg
4
1
0
Flash point−49.0 °C; −56.2 °F; 224.2 K
Autoignition temperature260.0 °C; 500.0 °F; 533.1 K
Explosive limits1.4–8.3%
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 dataUV, IR, NMR, MS
 YesY (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references
 
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Pentane
Identifiers
CAS number109-66-0 YesY
PubChem8003
ChemSpider7712 YesY
UNII4FEX897A91 YesY
EC number203-692-4
UN number1265
DrugBankDB03119
MeSHpentane
ChEBICHEBI:37830 YesY
ChEMBLCHEMBL16102 YesY
RTECS numberRZ9450000
Beilstein Reference969132
Gmelin Reference1766
Jmol-3D imagesImage 1
Properties[1]
Molecular formulaC5H12
Molar mass72.15 g mol−1
AppearanceColourless liquid
OdorOdourless
Density0.626 g mL−1
Melting point−130.5 to −129.1 °C; −202.8 to −200.3 °F; 142.7 to 144.1 K
Boiling point35.9 to 36.3 °C; 96.5 to 97.3 °F; 309.0 to 309.4 K
Solubility in water40 mg L−1 (at 20 °C)
log P3.255
Vapor pressure57.90 kPa (at 20.0 °C)
kH7.8 nmol Pa−1 kg−1
Acidity (pKa)~45
Basicity (pKb)~59
λmax200 nm
Refractive index (nD)1.358
Viscosity240 μPa s (at 20 °C)
Thermochemistry
Std enthalpy of
formation
ΔfHo298
−174.1–−172.9 kJ mol−1
Std enthalpy of
combustion
ΔcHo298
−3.5095–−3.5085 MJ mol−1
Standard molar
entropy
So298
263.47 J K−1 mol−1
Specific heat capacity, C167.19 J K−1 mol−1
Hazards
MSDSExternal MSDS
GHS pictogramsThe 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 wordDANGER
GHS hazard statementsH225, H304, H336, H411
GHS precautionary statementsP210, P261, P273, P301+310, P331
EU Index601-006-00-1
EU classificationFlammable F+ Harmful Xn Dangerous for the Environment (Nature) N
R-phrasesR12, R51/53, R65, R66, R67
S-phrases(S2), S16, S29, S33
NFPA 704
NFPA 704.svg
4
1
0
Flash point−49.0 °C; −56.2 °F; 224.2 K
Autoignition temperature260.0 °C; 500.0 °F; 533.1 K
Explosive limits1.4–8.3%
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 dataUV, IR, NMR, MS
 YesY (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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 "methylbutane" and "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 namenormal pentane
unbranched pentane
n-pentane
isopentaneneopentane
IUPAC namepentane2-methylbutane2,2-dimethylpropane
Molecular
diagram
N-Pentan.pngIsopentane.PNGNeopentane.PNG
Skeletal
diagram
Pentane-2D-Skeletal.svgIsopentane-2D-skeletal.pngNeopentane-2D-skeletal.png
Melting
Point (°C)[2]
−129.8−159.9−16.6
Boiling
Point (°C)[2]
36.027.79.5
Density (g/L)[2]621616586

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.

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.[3]

Rotation about two central single C-C bonds of n-pentane produces four different conformations.[4]

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. ^ From the values listed at Standard enthalpy change of formation (data table).
  4. ^ 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. doi:10.1021/jp809639s. PMID 19152252. 

External links[edit]