Isobutylene

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Isobutylene
Skeletal formula of isobutylene
Ball-and-stick model of isobutylene
Space-filling model of isobutylene
Names
Preferred IUPAC name
2-Methylprop-1-ene
Other names
2-Methylpropene
Isobutene
γ-Butylene
2-Methylpropylene
Methylpropene
Identifiers
  • 115-11-7 checkY
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.003.697 Edit this at Wikidata
EC Number
  • 204-066-3
RTECS number
  • UD0890000
UNII
UN number 1055
In Liquefied petroleum gas: 1075
  • InChI=1S/C4H8/c1-4(2)3/h1H2,2-3H3 checkY
    Key: VQTUBCCKSQIDNK-UHFFFAOYSA-N checkY
  • InChI=1/C4H8/c1-4(2)3/h1H2,2-3H3
  • CC(=C)C
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 pictograms Flam. Gas 1Press. Gas
GHS Signal word Danger
H220
P210, P377, P381, P403
NFPA 704 (fire diamond)
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).
☒N verify (what is checkY☒N ?)
Infobox references

Isobutylene (or 2-methylpropene) is a hydrocarbon with the 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]

Production[edit]

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 or ethanol.

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[edit]

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

Safety[edit]

Isobutylene is a highly flammable gas.

See also[edit]

References[edit]

  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.
  4. ^ Olah, George A.; Molnár, Árpád, Hydrocarbon Chemistry, Wiley-Interscience, ISBN 978-0-471-41782-8.
  5. ^ Lionel Delaude, Alfred F. Noels. "Metathesis". Kirk-Othmer Encyclopedia of Chemical Technology. Wiley.CS1 maint: uses authors parameter (link)
  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.

External links[edit]