Isobutylene
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| Names | |||
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| Preferred IUPAC name
2-Methylprop-1-ene | |||
| Other names
2-Methylpropene
Isobutene γ-Butylene 2-Methylpropylene Methylpropene | |||
| Identifiers | |||
3D model (JSmol)
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| ChEBI | |||
| ChemSpider | |||
| ECHA InfoCard | 100.003.697 | ||
| EC Number |
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PubChem CID
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| RTECS number |
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| UNII | |||
| UN number | 1055 In Liquefied petroleum gas: 1075 | ||
CompTox Dashboard (EPA)
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| Properties[1] | |||
| C4H8 | |||
| Molar mass | 56.106 g/mol | ||
| 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) | ||
| Insoluble | |||
| -44.4·10−6 cm3/mol | |||
| Hazards[2] | |||
| GHS labelling: | |||
 
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| Danger | |||
| H220 | |||
| P210, P377, P381, P403 | |||
| NFPA 704 (fire diamond) | |||
| Flash point | flammable gas | ||
| 465 °C (869 °F; 738 K) | |||
| Explosive limits | 1.8–9.6% | ||
| Related compounds | |||
Related butenes
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1-Butene cis-2-Butene trans-2-Butene | ||
Related compounds
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Isobutane | ||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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 colourless flammable gas but not highly flammable.
Uses
Isobutylene is used as an intermediate in the production of a variety of products. By reaction with methanol and ethanol, it is a precursor to the gasoline oxygenates methyl tert-butyl ether (MTBE) and ethyl tert-butyl ether (ETBE), respectively. Alkylation with butane produces isooctane, another fuel additive (similarly, isobutylene can be dimerized to diisobutylene (DIB), then hydrogenated to make isooctane). Isobutylene is also used in the production of methacrolein. Polymerization of isobutylene produces butyl rubber (polyisobutylene or PIB). Antioxidants such as butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA) are produced by Friedel-Crafts alkylation of phenols using isobutylene.
tert-Butylamine is produced commercially by amination of isobutylene using zeolite catalysts:[3]
- NH3 + CH2=C(CH3)2 → H2NC(CH3)3
Manufacture
Polymer and chemical grade isobutylene is typically obtained by dehydrating tertiary butyl alcohol (TBA) or catalytic dehydrogenation of isobutane (Catofin or similar processes).[4] Gasoline oxygenates MTBE and ETBE are produced by reacting methanol or ethanol with isobutylene contained in butene streams from olefin steam crackers or refineries, or with isobutylene from dehydrated TBA. Isobutylene is not isolated from the olefin or refinery butene stream before the reaction as separating the ethers from the remaining butenes is simpler. Isobutylene can also be produced in high purities by "back-cracking" MTBE or ETBE at high temperatures and then separating the isobutylene by distillation from the much higher boiling resulting alcohols.
By-product
In the ethenolysis of diisobutylene to prepare neohexene, isobutylene is a byproduct:[5]
- (CH3)3C-CH=C(CH3)2 + CH2=CH2 → (CH3)3C-CH=CH2 + (CH3)2C=CH2
Safety
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
References
- ^ The Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals (11th ed.), Merck, 1989, ISBN 091191028X, 5024.
- ^ a b Isobutene, International Chemical Safety Card 1027, Geneva: International Programme on Chemical Safety, April 2000
- ^ Eller, Karsten; Henkes, Erhard; Rossbacher, Roland; Höke, Hartmut (2000). "Amines, Aliphatic". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a02_001. ISBN 978-3527306732.
- ^ Olah, George A.; Molnár, Árpád, Hydrocarbon Chemistry, Wiley-Interscience, ISBN 978-0-471-41782-8.
- ^ "Metathesis". Kirk-Othmer Encyclopedia of Chemical Technology. Wiley.
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