Isobutylene

Isobutylene
IUPAC name 2-Methylpropene
Other names Isobutene γ-Butylene 2-Methylpropylene Methylpropene 2-Methylprop-2-ene
Identifiers
CAS number	115-11-7 Y
PubChem	8255
ChemSpider	7957 Y
UNII	QA2LMR467H Y
EC number	204-066-3
UN number	1055 In Liquefied petroleum gas: 1075
RTECS number	UD0890000
Jmol-3D images	Image 1
SMILES CC(=C)C
InChI InChI=1S/C4H8/c1-4(2)3/h1H2,2-3H3 Y Key: VQTUBCCKSQIDNK-UHFFFAOYSA-N Y InChI=1/C4H8/c1-4(2)3/h1H2,2-3H3
Properties[1]
Molecular formula	C4H8
Molar mass	56.11 g mol−1
Appearance	Colorless gas
Density	0.5879 g/cm3, liquid
Melting point	−140.3 ºC
Boiling point	-6.9 °C, 266 K, 20 °F
Solubility in water	Insoluble
Hazards[2]
GHS pictograms	Template:GHS04
GHS signal word	DANGER
GHS hazard statements	H220
GHS precautionary statements	P210, P377, P381, P403
EU Index	601-012-00-4
EU classification	Extremely flammable (F+)
R-phrases	R12
S-phrases	(S2), S9, S16, S33
NFPA 704	4 1 0
Flash point	flammable gas
Autoignition temperature	465 °C (869 ºF)
Explosive limits	1.8–9.6%
Related compounds
Related butenes	1-Butene cis-2-Butene trans-2-Butene
Related compounds	Isobutane
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Isobutylene (or 2-methylpropene) is a hydrocarbon of significant industrial importance. It is a four-carbon branched alkene (olefin), one of the four isomers of butylene. At standard temperature and pressure it is a colorless flammable gas.

Uses

Isobutylene is used as an intermediate in the production of a variety of products. It is reacted with methanol and ethanol in the manufacture of the gasoline oxygenates methyl tert-butyl ether (MTBE) and ethyl tert-butyl ether (ETBE), respectively. Alkylation with butane produces isooctane, another fuel additive. Isobutylene is also used in the production of methacrolein. Polymerization of isobutylene produces butyl rubber (polyisobutylene). Antioxidants such as butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA) are produced by Friedel-Crafts alkylation of phenols using isobutylene.

Manufacture

Isobutylene can be isolated from refinery streams by reaction with sulfuric acid, but the most common industrial method for its production is by catalytic dehydrogenation of isobutane.^[3] In the 1990s, the production of isobutylene increased dramatically as the demand for oxygenates such as MTBE grew. Key manufacturers of this product are Texas Petrochemicals(TPC Group) and Lyondell in North America.

Safety

Isobutylene is a highly flammable gas and presents an explosion danger. Usually stored as a compressed gas, if released it may produce an oxygen-deficient atmosphere that presents an asphyxiation hazard.^[2]

See also

• Butyl rubber
• Polybutene

References

1. ^ The Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals (11th ed.), Merck, 1989, ISBN 091191028X , 5024.
2. ^ ^{a b} Isobutene, International Chemical Safety Card 1027, Geneva: International Programme on Chemical Safety, April 2000, http://www.inchem.org/documents/icsc/icsc/eics1027.htm 
3. ^ Olah, George A.; Molnár, Árpád, Hydrocarbon Chemistry, Wiley-Interscience, ISBN 978-0471417828 .

External links

• International Chemical Safety Card 1027
• SIDS Initial Assessment Report for Isobutylene from the Organisation for Economic Co-operation and Development (OECD)