Pentane (C₅H₁₂)

Pentane is any or one of the organic compounds with the formula C₅H₁₂. This alkane is a component of some fuels and is employed as a specialty solvent in the laboratory. Its properties are very similar to those of butane and hexane. It exists in three structural isomers, the branched isomers are called isopentane and neopentane.

The branched isomers are more stable. That is, they have lower heat of formation and heat of combustion. Isopentane is more stable than pentane by 1.8 kcal/mol, and neopentane by 5 kcal/mol. Rotation about two central single C-C bonds produces four different conformations.

Laboratory use

As the most volatile hydrocarbon that is liquid at room temperature, pentane is often used in the laboratory as a solvent that can be conveniently evaporated. Also because of its nonpolarity and lack of functionality, its dissolving power is poor, thus only non-polar and alkyl-rich compounds are soluble in it. Pentane is miscible, however, with most common nonpolar solvents such as chlorocarbons, aromatics, and ethers.

One of its applications as a laboratory solvent is in liquid chromatography.

Reactions

Pentane burns to form carbon dioxide and water:

C₅H₁₂ + 8 O₂ → 5 CO₂ + 6 H₂O

As with other hydrocarbons, pentane undergoes free radical chlorination:

C₅H₁₂ + Cl₂ → C₅H₁₁Cl + HCl

Such reactions are unselective, yielding a mixture of the 1-, 2-, and 3-chloropentanes, as well as more highly chlorinated derivatives. Other radical halogenations can also occur.

While n-butane is the conventional feedstock in the production of maleic anhydride, pentane is also a substrate:

CH₃CH₂CH₂CH₂CH₃ + 5 O₂ → C₂H₂(CO)₂O + 5 H₂O + CO₂

Industrial Uses

Pentane is one of the primary blowing agents used in the production of polystyrene foam.

Pentane is used as a working medium in geothermal power stations.