関: isopentane

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/02/24 01:12:56」(JST)

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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 "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 name	normal pentane unbranched pentane n-pentane	isopentane	neopentane
IUPAC name	pentane	2-methylbutane	2,2-dimethylpropane
Molecular diagram
Skeletal diagram
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.

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]

^ Record of n-Pentane in the GESTIS Substance Database from the IFA, accessed on 19 April 2011
^ ^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
^ 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. doi:10.1021/jp809639s. PMID 19152252.

External links[edit]

International Chemical Safety Card 0534 at ILO.org
NIOSH Pocket Guide to Chemical Hazards at CDC.gov
Material safety data sheet for Pentane at Ox.ac.uk
Phytochemical data for pentane at Ars-grin.gov

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Related Pictures

★リンクテーブル★

リンク元	「ペンタン」
拡張検索	「carbetapentane」「cyclopentane」「isopentane」「aminocyclopentane」

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Pentane
	IUPAC name Pentane
Identifiers
CAS number	109-66-0
PubChem	8003
ChemSpider	7712
UNII	4FEX897A91
EC number	203-692-4
UN number	1265
DrugBank	DB03119
MeSH	pentane
ChEBI	CHEBI:37830
ChEMBL	CHEMBL16102
RTECS number	RZ9450000
Beilstein Reference	969132
Gmelin Reference	1766
Jmol-3D images	Image 1
	SMILES CCCCC ;
	InChI InChI=1S/C5H12/c1-3-5-4-2/h3-5H2,1-2H3 ; Key: OFBQJSOFQDEBGM-UHFFFAOYSA-N ;
Properties
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	240 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, C	167.19 J K−1 mol−1
Hazards
MSDS	External MSDS
GHS pictograms
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	F+ Xn N
R-phrases	R12, R51/53, R65, R66, R67
S-phrases	(S2), S16, S29, S33
NFPA 704	4 1 0
Flash point	−49.0 °C; −56.2 °F; 224.2 K
Autoignition temperature	260.0 °C; 500.0 °F; 533.1 K
Explosive limits	1.4–8.3%
LD50	3 g kg−1 (dermal, rabbit); 5 g kg−1 (oral, mouse);
Related compounds
Related alkanes	Butane; Butyl iodide; Hexane;
Supplementary data page
Structure and; properties	n, εr, etc.
Thermodynamic; data	Phase behaviour; Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
	(verify) (what is: /?); Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
	Infobox references