Pentane
Overview
 
Pentane is an organic compound
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...

 with the formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....

 C5H12 — that is, an alkane
Alkane
Alkanes are chemical compounds that consist only of hydrogen and carbon atoms and are bonded exclusively by single bonds without any cycles...

 with five carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

 atoms. The term may refer to any of three structural isomers
Structural isomerism
Structural isomerism, or constitutional isomerism , is a form of isomerism in which molecules with the same molecular formula have bonded together in different orders, as opposed to stereoisomerism. There are multiple synonyms for constitutional isomers.Three categories of constitutional 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
Cyclopentane
Cyclopentane is a highly flammable alicyclic hydrocarbon with chemical formula 510 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 occurs as a colorless liquid with a petrol-like odor. Its melting point is −94 °C...

 is not an isomer of pentane.

Pentanes are components of some fuels and are employed as specialty solvent
Solvent
A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...

s in the laboratory.
Encyclopedia
Pentane is an organic compound
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...

 with the formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....

 C5H12 — that is, an alkane
Alkane
Alkanes are chemical compounds that consist only of hydrogen and carbon atoms and are bonded exclusively by single bonds without any cycles...

 with five carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

 atoms. The term may refer to any of three structural isomers
Structural isomerism
Structural isomerism, or constitutional isomerism , is a form of isomerism in which molecules with the same molecular formula have bonded together in different orders, as opposed to stereoisomerism. There are multiple synonyms for constitutional isomers.Three categories of constitutional 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
Cyclopentane
Cyclopentane is a highly flammable alicyclic hydrocarbon with chemical formula 510 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 occurs as a colorless liquid with a petrol-like odor. Its melting point is −94 °C...

 is not an isomer of pentane.

Pentanes are components of some fuels and are employed as specialty solvent
Solvent
A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...

s in the laboratory. Their properties are very similar to those of butane
Butane
Butane is a gas with the formula C4H10 that is an alkane with four carbon atoms. The term may refer to any of two structural isomers, or to a mixture of them: in the IUPAC nomenclature, however, butane refers only to the unbranched n-butane isomer; the other one being called "methylpropane" or...

s and hexane
Hexane
Hexane is a hydrocarbon with the chemical formula C6H14; that is, an alkane with six carbon atoms.The term may refer to any of four other structural isomers with that formula, or to a mixture of them. In the IUPAC nomenclature, however, hexane is the unbranched isomer ; the other four structures...

s.

Isomers

Common name normal pentane
unbranched pentane
n-pentane
isopentane
Isopentane
Isopentane, C5H12, also called methylbutane or 2-methylbutane, is a branched-chain alkane with five carbon atoms. Isopentane is an extremely volatile and extremely flammable liquid at room temperature and pressure. The normal boiling point is just a few degrees above room temperature and...

neopentane
Neopentane
Neopentane, also called dimethylpropane, is a double-branched-chain alkane with five carbon atoms. Neopentane is an extremely flammable gas at room temperature and pressure which can condense into a highly volatile liquid on a cold day, in an ice bath, or when compressed to a higher...

IUPAC name pentane methylbutane dimethylpropane
Molecular
diagram
Skeletal
diagram

Industrial uses

Pentane is one of the primary blowing agents
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 when the blown material is in a liquid stage...

 used in the production of polystyrene foam.

Because of its low boiling point, low cost, and relative safety, pentane is used as a working medium in geothermal power
Geothermal power
Geothermal energy is thermal energy generated and stored in the Earth. Thermal energy is the energy that determines the temperature of matter. Earth's geothermal energy originates from the original formation of the planet and from radioactive decay of minerals...

 stations. It is added into some refrigerant
Refrigerant
A refrigerant is a substance used in a heat cycle usually including, for enhanced efficiency, a reversible phase change from a liquid to a gas. Traditionally, fluorocarbons, especially chlorofluorocarbons, were used as refrigerants, but they are being phased out because of their ozone depletion...

 blends as well.

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 solvent
Solvent
A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...

s that can be conveniently evaporated. However, because of their nonpolarity and lack of functionality
Functional group
In organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction regardless of the size of the molecule it is a part of...

, they can only dissolve non-polar and alkyl-rich compounds. Pentanes are miscible with most common nonpolar solvents such as chlorocarbons, aromatics, and ether
Ether
Ethers are a class of organic compounds that contain an ether group — an oxygen atom connected to two alkyl or aryl groups — of general formula R–O–R'. A typical example is the solvent and anesthetic diethyl ether, commonly referred to simply as "ether"...

s. They are also often used in liquid chromatography.

Physical properties

Melting point (MP), boiling point (BP) and density of pentanes
IsomerMP (°C)BP (°C) Density (g/L)
n-pentane −129.8 36.0 621
isopentane −159.9 27.7 616
neopentane −16.6 9.5 586


The boiling point
Boiling point
The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid....

s 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 point
Melting point
The melting point of a solid 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 depends on pressure and is usually specified at standard atmospheric pressure...

s 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.

The branched isomers are more stable (have lower heat of formation and heat of combustion
Heat of combustion
The heat of combustion is the energy released as heat when a compound undergoes complete combustion with oxygen under standard conditions. The chemical reaction is typically a hydrocarbon reacting with oxygen to form carbon dioxide, water and heat...

) than normal pentane. The difference is 1.8 kcal/mol for isopentane, and 5 kcal/mol for neopentane.

Rotation
Rotation
A rotation is a circular movement of an object around a center of rotation. A three-dimensional object rotates always around an imaginary line called a rotation axis. If the axis is within the body, and passes through its center of mass the body is said to rotate upon itself, or spin. A rotation...

 about two central single C-C bonds
Chemical bond
A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electromagnetic force attraction between opposite charges, either between electrons and nuclei, or as the result of a dipole attraction...

 of n-pentane produces four different conformations
Conformational isomerism
In chemistry, conformational isomerism is a form of stereoisomerism in which the isomers can be interconverted exclusively by rotations about formally single bonds...

.

Reactions

All pentane isomers burn with oxygen to form carbon dioxide and water:
C5H12 + 8 O2 → 5 CO2 + 6 H2O


As with other hydrocarbons, pentanes undergo free radical chlorination
Free radical halogenation
In organic chemistry, free-radical halogenation is a type of halogenation. This chemical reaction is typical of alkanes and alkyl-substituted aromatics under application of heat or UV light. The reaction is used for the industrial synthesis of chloroform , dichloromethane , and hexachlorobutadiene...

:
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 halogenation
Halogenation
Halogenation is a chemical reaction that incorporates a halogen atom into a molecule in substitution of hydrogen atom. Halogenation takes place in the gas phase. There are four types of halogenation: fluorination, chlorination, bromination, and iodination...

s can also occur.

While n-butane
Butane
Butane is a gas with the formula C4H10 that is an alkane with four carbon atoms. The term may refer to any of two structural isomers, or to a mixture of them: in the IUPAC nomenclature, however, butane refers only to the unbranched n-butane isomer; the other one being called "methylpropane" or...

 is the conventional feedstock in the production of maleic anhydride
Maleic anhydride
Maleic anhydride is an organic compound with the formula C2H22O. It is the acid anhydride of maleic acid and in its pure state it is a colourless or white solid with an acrid odour....

, n-pentane is also a substrate:
CH3CH2CH2CH2CH3 + 5 O2 → C2H2(CO)2O + 5 H2O + CO2

External links

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