Isobutane, also known as i-butane, 2-methylpropane or methylpropane, is a chemical compound with molecular formula HC(CH3)3. It is an isomer of butane. It is the simplest alkane with a tertiary carbon. Isobutane is used as a precursor molecule in the petrochemical industry, for example in the synthesis of isooctane.
|Preferred IUPAC name|
3D model (JSmol)
|E number||E943b (glazing agents, ...)|
CompTox Dashboard (EPA)
|Molar mass||58.124 g·mol−1|
|Melting point||−159.42 °C (−254.96 °F; 113.73 K)|
|Boiling point||−11.7 °C (10.9 °F; 261.4 K)|
|48.9 mg⋅L−1 (at 25 °C (77 °F))|
|Vapor pressure||3.1 atm (310 kPa) (at 21 °C (294 K; 70 °F))|
Heat capacity (C)
Std enthalpy of
|−134.8 – −133.6 kJ⋅mol−1|
Std enthalpy of
|−2.86959 – −2.86841 MJ⋅mol−1|
|Safety data sheet||See: data page|
|GHS Signal word||Danger|
|NFPA 704 (fire diamond)|
|Flash point||−83 °C (−117 °F; 190 K)|
|460 °C (860 °F; 733 K)|
|NIOSH (US health exposure limits):|
|TWA 800 ppm (1900 mg/m3)|
IDLH (Immediate danger)
|Supplementary data page|
|Refractive index (n),|
Dielectric constant (εr), etc.
|UV, IR, NMR, MS|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Isobutane is obtained by isomerization of butane.
Isobutane is the principal feedstock in alkylation units of refineries. Using isobutane, gasoline-grade "blendstocks" are generated with high branching for good combustion characteristics. Typical products from isobutane are 2,4-dimethylpentane and especially 2,2,4-trimethylpentane.
In the Chevron Phillips slurry process for making high-density polyethylene, isobutane is used as a diluent. As the slurried polyethylene is removed, isobutane is "flashed" off, and condensed, and recycled back into the loop reactor for this purpose.
Precursor to tert-butyl hydroperoxide
Isobutane is oxidized to tert-butyl hydroperoxide, which is subsequently reacted with propylene to yield propylene oxide. The tert-butanol that results as a by-product is typically used to make gasoline additives such as methyl tert-butyl ether (MTBE).
Isobutane is used as a refrigerant. The use in refrigerators started in 1993 when Greenpeace presented the Greenfreeze project with the German company Foron. In this regard, blends of pure, dry "isobutane" (R-600a) (that is, isobutane mixtures) have negligible ozone depletion potential and very low global warming potential (having a value of 3.3 times the GWP of carbon dioxide) and can serve as a functional replacement for R-12, R-22, R-134a, and other chlorofluorocarbon or hydrofluorocarbon refrigerants in conventional stationary refrigeration and air conditioning systems.
As a refrigerant, isobutane poses an explosion risk in addition to the hazards associated with non-flammable CFC refrigerants. Substitution of this refrigerant for motor vehicle air conditioning systems not originally designed for isobutane is widely prohibited or discouraged.
Vendors and advocates of hydrocarbon refrigerants argue against such bans on the grounds that there have been very few such incidents relative to the number of vehicle air conditioning systems filled with hydrocarbons.
The traditional name isobutane was still retained in the 1993 IUPAC recommendations, but is no longer recommended according to the 2013 recommendations. Since the longest continuous chain in isobutane contains only three carbon atoms, the preferred IUPAC name is 2-methylpropane but the locant (2-) is typically omitted in general nomenclature as redundant; C2 is the only position on a propane chain where a methyl substituent can be located without altering the main chain and forming the constitutional isomer n-butane.
- Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. p. 652. doi:10.1039/9781849733069-FP001. ISBN 978-0-85404-182-4.
The names ‘isobutane’, ‘isopentane’ and ‘neopentane’ are no longer recommended.
- Record in the GESTIS Substance Database of the Institute for Occupational Safety and Health
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- Patent Watch, July 31, 2006.
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- Panico, R.; & Powell, W. H. (Eds.) (1994). A Guide to IUPAC Nomenclature of Organic Compounds 1993. Oxford: Blackwell Science. ISBN 0-632-03488-2.CS1 maint: multiple names: authors list (link) CS1 maint: extra text: authors list (link) http://www.acdlabs.com/iupac/nomenclature/93/r93_679.htm