Pentane

Pentane

Names
IUPAC name Pentane
Identifiers
CAS Registry Number	Y
Beilstein Reference	969132
ChEBI	Y
ChEMBL	Y
ChemSpider	Y
DrugBank	Y
EC number	203-692-4
Gmelin Reference	1766
InChI InChI=1S/C5H12/c1-3-5-4-2/h3-5H2,1-2H3 Y Key: OFBQJSOFQDEBGM-UHFFFAOYSA-N Y
Jmol-3D images	Image
MeSH
PubChem
RTECS number	RZ9450000
SMILES CCCCC
UNII	Y
UN number	1265
Properties[1]
Chemical formula	C5H12
Molar mass	72.15 g·mol−1
Appearance	Colourless liquid
Odor	Gasoline-like[2]
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)
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)	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
Safety data sheet	See: data page
GHS pictograms
GHS signal word	DANGER
GHS hazard statements	H225, H304, H336, H411
GHS precautionary statements	P210, P261, P273, P301+310, P331
EU classification (DSD)	F+ Xn N
R-phrases	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; 533.2 K)
Explosive limits	1.5–7.8%[2]
Lethal dose or concentration (LD, LC):
LD50 (Median dose)	3 g kg−1 (dermal, rabbit) 5 g kg−1 (oral, mouse)
LC50 (Median concentration)	130,000 mg/m3 (mouse, 30 min) 128,200 ppm (mouse, 37 min) 325,000 mg/m3 (mouse, 2 hr)[3]
US health exposure limits (NIOSH):
PEL (Permissible)	TWA 1000 ppm (2950 mg/m3)[2]
REL (Recommended)	TWA 120 ppm (350 mg/m3) C 610 ppm (1800 mg/m3) [15-minute][2]
IDLH (Immediate danger	1500 ppm[2]
Related compounds
Related alkanes	Butane Butyl iodide Hexane
Supplementary data page
Structure and properties	Refractive index (n), Dielectric constant (εr), etc.
Thermodynamic data	Phase behaviour solid–liquid–gas
Spectral data	UV, IR, NMR, MS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y  (: Y/N?)

Pentane is an 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
Skeletal diagram
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

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