Pentane is an
organic compound
In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...
with the
formula C
5H
12—that is, an
alkane with five
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon ma ...
atoms. The term may refer to any of three
structural isomers
In chemistry, a structural isomer (or constitutional isomer in the IUPAC nomenclature) of a compound is another compound whose molecule has the same number of atoms of each element, but with logically distinct bonds between them. The term meta ...
, or to a mixture of them: in the
IUPAC
The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...
nomenclature, however, pentane means exclusively the ''n''-pentane isomer; the other two are called
isopentane
Isopentane, also called methylbutane or 2-methylbutane, is a branched-chain saturated hydrocarbon (an alkane) with five carbon atoms, with formula or .
Isopentane is an extremely volatile and extremely flammable liquid at room temperature and p ...
(methylbutane) and
neopentane (dimethylpropane).
Cyclopentane
Cyclopentane (also called C pentane) is a highly flammable alicyclic hydrocarbon with chemical formula C5H10 and CAS number 287-92-3, consisting of a ring of five carbon atoms each bonded with two hydrogen atoms above and below the plane. It occ ...
is not an isomer of pentane because it has only 10
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...
atoms where pentane has 12.
Pentanes are components of some fuels and are employed as specialty
solvent
A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...
s in the
laboratory
A laboratory (; ; colloquially lab) is a facility that provides controlled conditions in which scientific or technological research, experiments, and measurement may be performed. Laboratory services are provided in a variety of settings: physi ...
. Their properties are very similar to those of
butanes and
hexane
Hexane () is an organic compound, a straight-chain alkane with six carbon atoms and has the molecular formula C6H14.
It is a colorless liquid, odorless when pure, and with boiling points approximately . It is widely used as a cheap, relative ...
s.
Industrial uses
Pentanes are some of the primary
blowing agent
A blowing agent is a substance which is capable of producing a cellular structure via a foaming process in a variety of materials that undergo hardening or phase transition, such as polymers, plastics, and metals. They are typically applied wh ...
s 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
boiling points, low cost, and relative safety, pentanes are used as a
working medium in
geothermal power stations and
organic Rankine cycles. It is also used in some blended
refrigerants.
Pentanes are solvents in many ordinary products, e.g. in some
pesticides.
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
solvent
A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...
s that can be conveniently and rapidly evaporated. However, because of their
nonpolarity and lack of
functionality, they dissolve only nonpolar and alkyl-rich compounds. Pentanes are
miscible with most common nonpolar solvents such as
chlorocarbons,
aromatic
In chemistry, aromaticity is a chemical property of cyclic ( ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to satur ...
s, and
ether
In organic chemistry, ethers are a class of compounds that contain an ether group—an oxygen atom connected to two alkyl or aryl groups. They have the general formula , where R and R′ represent the alkyl or aryl groups. Ethers can again ...
s.
They are 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 thickly branched isomers tend to have lower boiling points.
The same tends to be true for the
melting point
The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depen ...
s 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
tetrahedral molecules 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 isomers are more stable (have lower
heat of formation
In chemistry and thermodynamics, the standard enthalpy of formation or standard heat of formation of a compound is the change of enthalpy during the formation of 1 mole of the substance from its constituent elements in their reference state, w ...
and
heat of combustion) than n-pentane. The difference is 1.8
kcal/
mol for isopentane, and 5 kcal/mol for neopentane.
Rotation about two central single C-C
bonds of ''n''-pentane produces four different
conformations.
Reactions and occurrence
Like other
alkanes
In organic chemistry, an alkane, or paraffin (a historical trivial name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in ...
, pentanes are largely unreactive at standard room temperature and conditions - however, with sufficient
activation energy
In chemistry and physics, activation energy is the minimum amount of energy that must be provided for compounds to result in a chemical reaction. The activation energy (''E''a) of a reaction is measured in joules per mole (J/mol), kilojoules p ...
(e.g., an open flame), they readily
oxidize
Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or ...
to form
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
and water:
:C
5H
12 + 8 O
2 → 5 CO
2 + 6 H
2O + heat/energy
Like other
alkanes
In organic chemistry, an alkane, or paraffin (a historical trivial name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in ...
, pentanes undergo
free radical chlorination:
:C
5H
12 + Cl
2 → C
5H
11Cl + 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.
Pentane is a component of exhaled breath for some individuals. A degradation product of unsaturated fatty acids, its presence is associated with certain diseases and cancers.
References
External links
International Chemical Safety Card 0534at ILO.org
at CDC.gov
Phytochemical data for pentaneat Ars-grin.gov
{{Hydrides by group
Alkanes
Hydrocarbon solvents