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| Names | |||
|---|---|---|---|
| Preferred IUPAC name 2-Methylprop-1-ene | |||
| Other names 2-Methylpropene Isobutene γ-Butylene 2-Methylpropylene Methylpropene | |||
| Identifiers | |||
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3D model (JSmol) | |||
| ChEBI | |||
| ChemSpider |
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| ECHA InfoCard | 100.003.697 | ||
| EC Number |
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| RTECS number |
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| UNII | |||
| UN number | 1055 InLiquefied petroleum gas:1075 | ||
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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) | ||
| −44.4·10−6 cm3/mol | |||
| Structure | |||
| C2v | |||
| Hazards[2] | |||
| GHS labelling: | |||
  | |||
| 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 | |||
Relatedbutenes | 1-Butene cis-2-Butene trans-2-Butene | ||
Related compounds | Isobutane | ||
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |||
Isobutylene (or2-methylpropene) is ahydrocarbon with thechemical formula(CH3)2C=CH2. It is a four-carbon branchedalkene (olefin), one of the fourisomers of butylene. It is a colorless flammable gas, and is of considerable industrial value.[3]
Polymer and chemical grade isobutylene is typically obtained by dehydratingtertiary butyl alcohol (TBA) orcatalyticdehydrogenation ofisobutane.[4] Gasoline additivesmethyl tert-butyl ether (MTBE) andethyl tert-butyl ether (ETBE), respectively, are produced by reactingmethanol orethanol 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 methanol.
Isobutylene is a byproduct in theethenolysis ofdiisobutene to prepareneohexene:[5]
Isobutylene is used in the production of a variety of products. It is alkylated with butane to produceisooctane or dimerized to diisobutylene (DIB) and then hydrogenated to makeisooctane, a fuel additive. Isobutylene is also used in the production ofmethacrolein.Polymerization of isobutylene producesbutyl rubber (polyisobutylene or PIB). Antioxidants such asbutylated hydroxytoluene (BHT) andbutylated hydroxyanisole (BHA) are produced byFriedel-Crafts alkylation ofphenols with isobutylene.
tert-Butylamine is produced commercially by amination of isobutylene usingzeolitecatalysts:[6]
Applications are found in the calibration ofphotoionization detectors.
Isobutylene is a highly flammable gas.
