Isobutylene

Isobutylene
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IUPAC name	2-Methylpropene
Other names	Isobutene gamma-Butylene 2-Methylpropylene
Identifiers
CAS number	115-11-7
PubChem	8255
EINECS number	204-066-3
SMILES	CC(=C)C
InChI	InChI=1/C4H8/c1-4(2)3/h1H2,2-3H3
Properties
Molecular formula	C4H8
Molar mass	56.11 g mol-1
Appearance	Colorless gas
Density	0.5879 g/cm3
Boiling point	-6.9 °C, 266 K, 20 °F
Solubility in water	Insoluble
Hazards
Flash point	< -10 °C
Autoignition temperature	465 °C
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Isobutylene is a hydrocarbon of significant industrial importance. It is a four-carbon branched alkene (olefin), one of the 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 manufacture of 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. In the 1990s, the production of isobutylene increased dramatically as the demand for oxygenates such as MTBE grew.

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.