Butane (C₄H₁₀)

Butane, also called n-butane, is the unbranched alkane with four carbon atoms, CH₃CH₂CH₂CH₃. Butane is also used as a collective term for n-butane together with its only other isomer, isobutane (also called methylpropane), CH(CH₃)₃.

Butanes are highly flammable, colorless, odorless, easily liquefied gases. The name butane comes from the roots but- (from butyric acid) and -ane.

Rotation about a central C-C bond produces two different conformations (trans and gauche).

Reactions and uses

When oxygen is plentiful, butane burns to form carbon dioxide and water vapor; when oxygen is limited, carbon (soot) or carbon monoxide may also be formed.

2C₄H₁₀ + 13 O₂ → 8 CO₂ + 10 H₂O

n-Butane is the feedstock for DuPont's catalytic process for the preparation of maleic anhydride:

2 CH₃CH₂CH₂CH₃ + 7 O₂ → 2 C₂H₂(CO)₂O + 8 H₂O

n-Butane, like all hydrocarbons, undergoes free radical chlorination providing both 1-chloro- and 2-chlorobutanes, as well as more highly chlorinated derivatives. The relative rates of the chlorination is partially explained by the differing bond dissociation energies, 425 and 411 kJ/mol for the two types of C-H bonds. The two central carbon atoms have the slightly weaker C-H bonds.

Butane gas is sold bottled as a fuel for cooking and camping. When blended with propane and other hydrocarbons, it is referred to commercially as LPG. It is also used as a petrol component, as a feedstock for the production of base petrochemicals in steam cracking, as fuel for cigarette lighters and as a propellant in aerosol sprays such as deodorants.

Very pure forms of butane, especially isobutane, can be used as refrigerants and have largely replaced the ozone layer-depleting halomethanes, for instance in household refrigerators and freezers. The flammability of butane is not a major issue because the amount of butane in an appliance is not enough to cause a combustible mix given the amount of air in a room. The system operating pressure for butane is lower than for the halomethanes, such as R-12, so R-12 systems such as in automotive air conditioning systems, when converted to butane will not function optimally.

Effects and health issues

Inhalation of butane can cause euphoria, drowsiness, narcosis, asphyxia, cardiac arrhythmia, and frostbite which can result in death from asphyxiation and ventricular fibrillation. Butane is the most commonly misused volatile substance in the UK, and was the cause of 52% of "solvent related" deaths in 2000. By spraying butane directly into the throat, the jet of fluid can cool rapidly to –20 °C by expansion, causing prolonged laryngospasm. "Sudden sniffer's death" syndrome, first described by Bass in 1970, is the most common single cause of "solvent related" death, resulting in 55% of known fatal cases.