Preferred IUPAC name
Other names
Isobutane (no longer recommended[1])
75-28-5 YesY
3D model (Jmol) Interactive image
ChEBI CHEBI:30363 YesY
ChemSpider 6120 YesY
ECHA InfoCard 100.000.780
EC Number 200-857-2
E number E943b (glazing agents, ...)
KEGG D04623 N
PubChem 6360
RTECS number TZ4300000
UN number 1969
Molar mass 58.12 g·mol−1
Appearance Colorless gas
Odor Odorless
Density 2.51 kg/m3 (at 15 °C, 100 kPa)
Melting point −159.42 °C (−254.96 °F; 113.73 K)[2]
Boiling point −11.7 °C (10.9 °F; 261.4 K)[2]
Vapor pressure 204.8 kPa (at 21 °C (70 °F))
8.6 nmol Pa−1 kg−1
96.65 J K−1 mol−1
−134.8–−133.6 kJ mol−1
−2.86959–−2.86841 MJ mol−1
Safety data sheet See: data page
GHS pictograms
GHS signal word DANGER
R-phrases R12
S-phrases (S2), S16
NFPA 704
Flammability code 4: Will rapidly or completely vaporize at normal atmospheric pressure and temperature, or is readily dispersed in air and will burn readily. Flash point below 23 °C (73 °F). E.g., propane Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point −83 °C (−117 °F; 190 K)
460 °C (860 °F; 733 K)
Explosive limits 1.4–8.3%
US health exposure limits (NIOSH):
PEL (Permissible)
REL (Recommended)
TWA 800 ppm (1900 mg/m3)[3]
IDLH (Immediate danger)
Related compounds
Related alkane
Supplementary data page
Refractive index (n),
Dielectric constantr), etc.
Phase behaviour
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YesYN ?)
Infobox references

Isobutane (i-butane), also known as methylpropane, is a chemical compound with molecular formula C
and is an isomer of butane. It is the simplest alkane with a tertiary carbon. 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, and as a propellant in aerosol sprays. When used as a refrigerant or a propellant, isobutane is also known as R-600a. Some portable camp stoves use a mixture of isobutane with propane, usually 80:20. Isobutane is used as a feedstock in the petrochemical industry, for example in the synthesis of isooctane.[4]


The traditional name isobutane was still retained in the 1993 IUPAC recommendations,[5] but is no longer recommended according to the 2013 recommendations.[1] 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.


Isobutane is used as a refrigerant.[6] The use in refrigerators started in 1993 when Greenpeace presented the Greenfreeze project with the German company Foron.[7] 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.

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.[8]

Isobutane is also used as a propellant for aerosol cans and foam products.

Isobutane is used as part of blended fuels, especially common in fuel canisters used for camping.[9]

Isobutane is also used as a raw material in the manufacture of propylene oxide, where it is oxidized to tert-butyl hydroperoxide and 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).

Refrigerant use

As a refrigerant, isobutane has an explosion risk in addition to the hazards associated with non-flammable CFC refrigerants. Reports surfaced in late 2009 suggesting the use of isobutane as a refrigerant in domestic refrigerators was potentially dangerous. One refrigerator explosion reported in the United Kingdom was suspected to have been caused as a result of isobutane leaking into the refrigerator cabinet and being ignited by sparks in the electrical system.[10] Although unclear how serious this could be, at the time this report came out it was estimated 300 million refrigerators worldwide use isobutane as a refrigerant.

Substitution of this refrigerant for motor vehicle air conditioning systems not originally designed for isobutane is widely prohibited or discouraged, on the grounds that using flammable hydrocarbons in systems originally designed to carry non-flammable refrigerant presents a significant risk of fire or explosion.[11][12][13][14][15][16][17]

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.[18][19]


  1. 1 2 3 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.
  2. 1 2 Record in the GESTIS Substance Database of the IFA
  3. 1 2 3 "NIOSH Pocket Guide to Chemical Hazards #0350". National Institute for Occupational Safety and Health (NIOSH).
  4. Patent Watch, July 31, 2006.
  5. Panico, R.; & Powell, W. H. (Eds.) (1994). A Guide to IUPAC Nomenclature of Organic Compounds 1993. Oxford: Blackwell Science. ISBN 0-632-03488-2.
  6. "European Commission on retrofit refrigerants for stationary applications" (PDF). Retrieved 2010-10-29.
  7. Page - March 15, 2010 (2010-03-15). "GreenFreeze". Greenpeace. Retrieved 2013-01-02.
  8. Kenneth S. Whiteley (2005), "Polyethylene", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a21_487.pub2
  9. Rietveld, Will (2005-02-08). "Frequently Asked Questions About Lightweight Canister Stoves and Fuels". Backpacking Light. Retrieved 2014-07-26.
  10. Bingham, John (September 1, 2009). "Exploding fridges: ozone friendly gas theory for mystery blasts". The Daily Telegraph. London. Retrieved May 5, 2010.
  11. "U.S. EPA hydrocarbon-refrigerants FAQ". Retrieved 2010-10-29.
  12. Compendium of hydrocarbon-refrigerant policy statements, October 2006
  13. "MACS bulletin: hydrocarbon refrigerant usage in vehicles" (PDF). Retrieved 2010-10-29.
  14. "Society of Automotive Engineers hydrocarbon refrigerant bulletin". 2005-04-27. Retrieved 2010-10-29.
  15. "Saskatchewan Labour bulletin on hydrocarbon refrigerants in vehicles". 2010-06-29. Retrieved 2010-10-29.
  16. VASA on refrigerant legality & advisability Archived January 13, 2009, at the Wayback Machine.
  17. "Queensland (Australia) government warning on hydrocarbon refrigerants" (PDF). Retrieved 2010-10-29.
  18. "New South Wales (Australia) Parliamentary record, 16 October 1997". 1997-10-16. Retrieved 2010-10-29.
  19. "New South Wales (Australia) Parliamentary record, 29 June 2000". Retrieved 2010-10-29.

External links

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