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Skeletal formula Space-filling model
Ball-and-stick model
CAS number 115-11-7 YesY
PubChem 8255
ChemSpider 7957 YesY
EC number 204-066-3
UN number 1055
In Liquefied petroleum gas: 1075
RTECS number UD0890000
Jmol-3D images Image 1
Molecular formula C4H8
Molar mass 56.11 g mol−1
Appearance Colorless gas
Density 0.5879 g/cm3, liquid
Melting point −140.3 °C (−220.5 °F; 132.8 K)
Boiling point −6.9 °C (19.6 °F; 266.2 K)
Solubility in water Insoluble
GHS pictograms Flam. Gas 1Press. Gas
GHS signal word DANGER
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
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 flammable gas
Autoignition temperature 465 °C (869 °F; 738 K)
Explosive limits 1.8–9.6%
Related compounds
Related butenes 1-Butene
Related compounds Isobutane
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

Isobutylene (or 2-methylpropene) is a hydrocarbon of industrial significance. 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.


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.


Polymer and chemical grade isobutylene is typically obtained by dehydrating tertiary butyl alcohol or catalytic dehydrogenation of isobutane.[3] Gasoline oxygenates MTBE and ETBE are generally produced by reacting methanol or ethanol with isobutylene contained in butene streams from olefin steam crackers or refineries. Isobutylene is not isolated before the reaction as separating the ethers from the remaining butenes is simpler.


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

See also[edit]


  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 
  3. ^ Olah, George A.; Molnár, Árpád, Hydrocarbon Chemistry, Wiley-Interscience, ISBN 978-0-471-41782-8 .

External links[edit]