Butane

Author: Hans Lohninger

Butane, C₄H₁₀, belongs to the group of alkanes. The term butane may refer to any of two structural isomers (n-butane and isobutane⁽¹⁾), which differ considerably in their physical properties:

	n-butane	isobutane
Chemical Structure
Density (g) 15 °C, 1 atm	2.52 kg/m3	2.51 kg/m3
Density (l) at boiling point, 1 atm	601.4 kg/m3	593.4 kg/m3
Melting point	-138.4 °C	-159.6 °C
Boiling point	-0.5 °C	-11.7 °C

Both isomers of butane are highly flammable, colorless, odorless,⁽²⁾ easily liquefied gases. Butane gas is sold bottled as a fuel for cooking and camping, and as a fuel for cigarette lighters. Butane is also contained as a propellant in aerosol sprays. Isobutane is used as a refrigerant in household refrigerators and freezers and has largely replaced the ozone layer-depleting fluoro-chloro-hydrocarbons. Butane is extremely stable, has no corrosive action to metals, is slightly soluble in water (about 3.2 vol-% at 20°C) and is readily soluble in ethanol, ethyl ether, or chloroform.

Isobutane (in mixture with argon) is used in Geiger counters, as a reagent gas in chemical ionization mass spectrometry, and as a quentching gas for the detector in X Ray Fluorescence (XRF).

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In oxygen-rich environments butane burns to form carbon dioxide and water vapor (with a flame temperature up to 1900 °C):

2 C₄H₁₀ + 13 O₂ 8 CO₂ + 10 H₂O

n-Butane is the feedstock 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. The chlorine radicals have to generated by UV radiation:

2 C₄H₁₀ + Cl₂ 2 C₄H₉Cl

(1)	Please note that there are several chemical names for isobutane: trimethylmethane; 1,1-dimethylethane; 2-methylpropane; and i-butane.
(2)	Small amounts of thiols are added to cooking and camping gas in order to be able to smell any gas leakage.