Isobutane

Isobutane

Names
Preferred IUPAC name 2-Methylpropane[1]
Other names Isobutane (no longer recommended[1])
Identifiers
CAS Number	75-28-5 Y
3D model (Jmol)	Interactive image
Beilstein Reference	1730720
ChEBI	CHEBI:30363 Y
ChemSpider	6120 Y
ECHA InfoCard	100.000.780
EC Number	200-857-2
E number	E943b (glazing agents, ...)
Gmelin Reference	1301
KEGG	D04623 N
PubChem	6360
RTECS number	TZ4300000
UNII	BXR49TP611 Y
UN number	1969
InChI InChI=1S/C4H10/c1-4(2)3/h4H,1-3H3 Y Key: NNPPMTNAJDCUHE-UHFFFAOYSA-N Y
SMILES CC(C)C
Properties
Chemical formula	C4H10
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))
Henry's law constant (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
Safety data sheet	See: data page praxair.com
GHS pictograms
GHS signal word	DANGER
GHS hazard statements	H220
GHS precautionary statements	P210
EU classification (DSD)	F+
R-phrases	R12
S-phrases	(S2), S16
NFPA 704	4 1 0
Flash point	−83 °C (−117 °F; 190 K)
Autoignition temperature	460 °C (860 °F; 733 K)
Explosive limits	1.4–8.3%
US health exposure limits (NIOSH):
PEL (Permissible)	none[3]
REL (Recommended)	TWA 800 ppm (1900 mg/m3)[3]
IDLH (Immediate danger)	N.D.[3]
Related compounds
Related alkane	Isopentane
Supplementary data page
Structure and properties	Refractive index (n), Dielectric constant (εr), etc.
Thermodynamic data	Phase behaviour solid–liquid–gas
Spectral data	UV, IR, NMR, MS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

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

Nomenclature

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.

• The two isomers of butane
• 

  n-Butane

• 

  Isobutane (methylpropane)

Uses

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]

References

External links

• International Chemical Safety Card 0901
• NIOSH Pocket Guide to Chemical Hazards