Butane is an alkane hydrocarbon with the molecular formula C4H10. It has the following display formula:
H H H H | | | | H - C - C - C - C - H | | | | H H H H
It is a flammable, colorless, easily liquefied gas that is used extensively as a fuel for cigarette lighters and portable stoves.
Butane exists as two isomers:
n-butane is a fully hydrogenated linear chain of four carbon atoms: CH3CH2CH2CH3. Its boiling point is −0.6 °C and its melting point is −138.3 °C.
i-butane, or isobutane, has the formula CH3CH(CH3)2, and the systematic name 2-methylpropane. Its boiling point is −11.7 °C and its melting point is −159.6 °C.
Recent concerns with depletion of the ozone layer by freon gases have led to increased use of isobutane as a gas for refrigeration systems, especially in domestic refrigerators and freezers. When used as a refrigerant, isobutane is also known as R600a.
Alkanes are unreactive, as their C-C and C-H bonds are very strong. They do not react with acids, alkalis, metals, or oxidising agents. It may seem surprising, but petrol (octane) has no reaction with concentrated sulphuric acid, sodium metal or potassium manganate.
Butane gas is commonly used as bottled gas for cooking. Butane is commonly used as a camping gas called calor gas. It burns to form carbon dioxide and steam:
butane + oxygen -> carbon dioxide + steam
Burning camping gas forms carbon dioxide and steam (plentiful supply of air) and also carbon (soot) and carbon monoxide (in a limited supply of air).