Isobutylene

Last updated
Isobutylene
Isobutylene.svg
Ball-and-stick model of isobutylene Isobutylene-3D-balls.png
Ball-and-stick model of isobutylene
Space-filling model of isobutylene Isobutylene-3D-vdW.png
Space-filling model of isobutylene
Names
Preferred IUPAC name
2-Methylprop-1-ene
Other names
2-Methylpropene
Isobutene
γ-Butylene
2-Methylpropylene
Methylpropene
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.003.697 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 204-066-3
PubChem CID
RTECS number
  • UD0890000
UNII
UN number 1055
In Liquefied petroleum gas: 1075
  • InChI=1S/C4H8/c1-4(2)3/h1H2,2-3H3 Yes check.svgY
    Key: VQTUBCCKSQIDNK-UHFFFAOYSA-N Yes check.svgY
  • InChI=1/C4H8/c1-4(2)3/h1H2,2-3H3
  • CC(=C)C
Properties [1]
C4H8
Molar mass 56.106 g/mol
AppearanceColorless 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
Hazards [2]
GHS labelling:
GHS-pictogram-flamme.svg GHS-pictogram-exclam.svg
Danger
H220
P210, P377, P381, P403
NFPA 704 (fire diamond)
NFPA 704.svgHealth 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineFlammability 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. propaneInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
1
4
0
Flash point flammable gas
465 °C (869 °F; 738 K)
Explosive limits 1.8–9.6%
Related compounds
Related butenes
1-Butene
cis-2-Butene
trans-2-Butene
Related compounds
 Isobutane
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)

Isobutylene (or 2-methylpropene) is a hydrocarbon with the chemical formula (CH3)2C=CH2. It is a four-carbon branched alkene (olefin), one of the four isomers of butylene. It is a colorless flammable gas, and is of considerable industrial value. [3]

Contents

Production

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 additives methyl tert-butyl ether (MTBE) and ethyl tert-butyl ether (ETBE), respectively, 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 methanol.

Isobutylene is a byproduct in the ethenolysis of diisobutylene to prepare neohexene: [5]

(CH3)3C-CH=C(CH3)2 + CH2=CH2 → (CH3)3C-CH=CH2 + (CH3)2C=CH2

Uses

Isobutylene is used in the production of a variety of products. It is alkylated with butane to produce isooctane or dimerized to diisobutylene (DIB) and then hydrogenated to make isooctane, a fuel additive. 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 with isobutylene.

tert-Butylamine is produced commercially by amination of isobutylene using zeolite catalysts: [6]

NH3 + CH2=C(CH3)2 → H2NC(CH3)3

Applications are found in the calibration of photoionization detectors.

Safety

Isobutylene is a highly flammable gas.

See also

Related Research Articles

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<span class="mw-page-title-main">Ethyl vinyl ether</span> Chemical compound

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References

  1. ↑ The Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals (11th ed.), Merck, 1989, ISBN   091191028X ,5024.
  2. ↑ Isobutene, International Chemical Safety Card 1027, Geneva: International Programme on Chemical Safety, April 2000
  3. ↑ Geilen, Frank M.A.; Stochniol, Guido; Peitz, Stephan; Schulte-Koerne, Ekkehard (2014). "Butenes". Ullmann's Encyclopedia of Industrial Chemistry . Weinheim: Wiley-VCH. doi:10.1002/14356007.a04_483.pub3. ISBN   978-3527306732.
  4. ↑ Olah, George A.; Molnár, Árpád (May 2003), Hydrocarbon Chemistry, Wiley-Interscience, ISBN   978-0-471-41782-8 .
  5. ↑ Lionel Delaude; Alfred F. Noels. "Metathesis". Kirk-Othmer Encyclopedia of Chemical Technology. Wiley.
  6. ↑ 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.
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