Isobutane

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Isobutane
Skeletal formula of isobutane
Skeletal formula of isobutane with all implicit carbons shown, and all explicit hydrogens added
Ball and stick model of isobutane Spacefill model of isobutane
Identifiers
CAS number 75-28-5 YesY
PubChem 6360
ChemSpider 6120 YesY
UNII BXR49TP611 YesY
EC number 200-857-2
UN number 1969
KEGG D04623 N
ChEBI CHEBI:30363 YesY
RTECS number TZ4300000
Beilstein Reference 1730720
Gmelin Reference 1301
Jmol-3D images Image 1
Properties
Molecular formula C4H10
Molar mass 58.12 g mol−1
Appearance Colorless gas
Odor Odorless
Density 2.51 mg mL−1 (at 15 °C, 100 kPa)
Melting point −233.2 to −33.1 °C; −387.7 to −27.7 °F; 40.0 to 240.0 K
Boiling point −13 to −9 °C; 8 to 16 °F; 260 to 264 K
Vapor pressure 204.8 kPa (at 21 °C)
kH 8.6 nmol Pa−1 kg−1
Thermochemistry
Specific
heat capacity
C
96.65 J K−1 mol−1
Std enthalpy of
formation
ΔfHo298
−134.8–−133.6 kJ mol−1
Std enthalpy of
combustion
ΔcHo298
−2.86959–−2.86841 MJ mol−1
Hazards
MSDS External MSDS
GHS pictograms The flame pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)
GHS signal word DANGER
GHS hazard statements H220
GHS precautionary statements P210
EU Index 601-004-00-0
EU classification Flammable F+
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)
Explosive limits 1.4–8.3%
Related compounds
Related alkane Isopentane
Supplementary data page
Structure and
properties
n, εr, etc.
Thermodynamic
data
Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
Infobox references

Isobutane (i-butane), also known as methylpropane, is a chemical compound with molecular formula C
4
H
10
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.[2] Isobutane is used as a feedstock in the petrochemical industry, for example in the synthesis of isooctane.[3]

Nomenclature[edit]

Isobutane is the trivial name retained by the International Union of Pure and Applied Chemistry (IUPAC) in its 1993 Recommendations for the Nomenclature of Organic Chemistry.[4] Since the longest continuous chain in isobutane contains only three carbon atoms, the full systematic name is 2-methylpropane but the locant (2-) is typically omitted as redundant; C2 is the only position on a propane chain where a methyl substituent can be located without altering the main chain.

Uses[edit]

Isobutane is used as a refrigerant.[5] The use in refrigerators started in 1993 when Greenpeace presented the Greenfreeze project with the German company Foron.[6] 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.[7]

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

Refrigerant use[edit]

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. Several refrigerator explosions reported in the United Kingdom are suspected to have been caused as a result of isobutane leaking into the refrigerator cabinet and being ignited by sparks in the electrical system.[8] 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.[9][10][11][12][13][14][15]

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.[16][17]

References[edit]

  1. ^ "ISOBUTANE - Compound Summary". PubChem Compound. USA: National Center for Biotechnology Information. 16 September 2004. Identification and Related Records. Retrieved 5 March 2012. 
  2. ^ MSR Isopro
  3. ^ Patent Watch, July 31, 2006.
  4. ^ Panico, R.; & Powell, W. H. (Eds.) (1994). A Guide to IUPAC Nomenclature of Organic Compounds 1993. Oxford: Blackwell Science. ISBN 0-632-03488-2.  http://www.acdlabs.com/iupac/nomenclature/93/r93_679.htm
  5. ^ "European Commission on retrofit refrigerants for stationary applications" (PDF). Retrieved 2010-10-29. 
  6. ^ Page - March 15, 2010 (2010-03-15). "GreenFreeze". Greenpeace. Retrieved 2013-01-02. 
  7. ^ Kenneth S. Whiteley (2005), "Polyethylene", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a21_487.pub2 
  8. ^ Bingham, John (September 1, 2009). "Exploding fridges: ozone friendly gas theory for mystery blasts". The Daily Telegraph (London). Retrieved May 5, 2010. 
  9. ^ "U.S. EPA hydrocarbon-refrigerants FAQ". Epa.gov. Retrieved 2010-10-29. 
  10. ^ Compendium of hydrocarbon-refrigerant policy statements, October 2006[dead link]
  11. ^ "MACS bulletin: hydrocarbon refrigerant usage in vehicles" (PDF). Retrieved 2010-10-29. 
  12. ^ "Society of Automotive Engineers hydrocarbon refrigerant bulletin". Sae.org. 2005-04-27. Retrieved 2010-10-29. 
  13. ^ "Saskatchewan Labour bulletin on hydrocarbon refrigerants in vehicles". Labour.gov.sk.ca. 2010-06-29. Retrieved 2010-10-29. 
  14. ^ VASA on refrigerant legality & advisability[dead link]
  15. ^ "Queensland (Australia) government warning on hydrocarbon refrigerants". Energy.qld.gov.au. Retrieved 2010-10-29. 
  16. ^ "New South Wales (Australia) Parliamentary record, 16 October 1997". Parliament.nsw.gov.au. 1997-10-16. Retrieved 2010-10-29. 
  17. ^ "New South Wales (Australia) Parliamentary record, 29 June 2000". Parliament.nsw.gov.au. Retrieved 2010-10-29. 

External links[edit]