Pentane

 ( Alkanes ) 

Pentane is an organic compound with the chemical 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, in which case pentanes refers to a mixture of them; the other two are called isopentane (methylbutane) and neopentane (dimethylpropane). Cyclopentane is not an isomer of pentane because it has only 10 hydrogen atoms where pentane has 12.

Pentanes are components of some fuels and are employed as specialty in the laboratory. Their properties are very similar to those of and .

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History Normal pentane was discovered in 1862 by Carl Schorlemmer, who, while analyzing pyrolysis products of the cannel coal mined in Wigan, identified, separated by fractional distillation and studied a series of liquid hydrocarbons inert to Nitric acid and Sulfuric acid acids. The lightest of them, which he called hydride of amyl, had an empirical formula of C₅H₁₂, density of 0.636 at 17 °C and boiled between 39 and 40 °C. In the next year he identified the same compound in the Pennsylvanian oil. By 1872 he switched his nomenclature to the modern one, leading to it being called Pentane.

Beyond Schorlemmer's initial work, scientists discovered that the molecular formula C₅H₁₂ could represent different structural arrangements, leading to the identification of isopentane and neopentane. This discovery contributed significantly to the understanding of Isomer and Hydrocarbon in the 19th century. The high volatility and low boiling point of pentane made it useful as a solvent and in fuels. Its use expanded in the 1970s as a blowing agent for foams, replacing CFCs. The petroleum refining industry utilizes pentanes, particularly isopentane, to produce high-octane fuels.

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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)	−129.8	−159.9	−16.6
Boiling point (°C)	36.0	27.7	9.5
Density (0 °C,kg/m3)	699	616	586

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Industrial uses Pentanes are some of the primary used in the production of polystyrene foam and other foams. Usually, a mixture of n-, i-, and increasingly cyclopentane is used for this purpose.

Acid-catalyzed isomerization gives isopentane, which is used in producing high-octane fuels.

Because of their low , low cost, and relative safety, pentanes are used as a working fluid in geothermal power stations and organic Rankine cycles. It is also used in some blended .

Pentanes are solvents in many ordinary products, e.g. in some .

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Laboratory use Pentanes are relatively inexpensive and are the most volatile liquid alkanes at room temperature, so they are often used in the laboratory as that can be conveniently and rapidly evaporated. However, because of their and lack of functional group, they dissolve only nonpolar and alkyl-rich compounds. Pentanes are miscible with most common nonpolar solvents such as , , and .

They are often used in liquid chromatography.

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Physical properties The of the pentane isomers range from about 9 to 36 °C. As is the case for other alkanes, the more thickly branched isomers tend to have lower boiling points.

The same tends to be true for the of alkane isomers, and 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 Tetrahedron packing more closely in solid form; this explanation is contradicted by the fact that neopentane has a lower density than the other two isomers, and the high melting point is actually caused by neopentane's significantly lower entropy of fusion.

The branched are more stable (have lower heat of formation and heat of combustion) than n-pentane. The difference is 1.8 KCal/mol for isopentane, and 5 kcal/mol for neopentane.From the values listed at Standard enthalpy change of formation (data table).

Rotation about two central single C-C Chemical bond of n-pentane produces four different conformations.

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Reactions Like other alkanes, pentanes are largely unreactive at standard room temperature and conditions - however, with sufficient activation energy (e.g., an open flame), they readily Redox 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

Without zeolite catalysts, such reactions are unselective, so with n-pentane, the result is a mixture of the 1-, 2-, and 3-chloropentanes, as well as more highly chlorinated derivatives. Other radical can also occur.

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Production and occurrence Pentane is produced by fractional distillation of petroleum and purified by rectification (successive distillations).

It occurs in alcoholic beverages and in hops. It is a component of exhaled breath for some individuals. A degradation product of unsaturated fatty acids, its presence is associated with some diseases and cancers.

Pentane is a relatively minor component of automobile gasoline, with its share varying within 1–6% in 1990s Sweden, 2–13% in 1990s US and 1–3% in the US in 2011. At 62, its octane number (both RON and MON) is quite low.

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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

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