Isobutylene

Unsaturated hydrocarbon compound (H2C=C(CH3)2)
Isobutylene
Skeletal formula of isobutylene
Ball-and-stick model of isobutylene
Ball-and-stick model of isobutylene
Space-filling 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
CAS Number
  • 115-11-7 checkY
3D model (JSmol)
  • Interactive image
ChEBI
  • CHEBI:43907 ☒N
ChemSpider
  • 7957 checkY
ECHA InfoCard 100.003.697 Edit this at Wikidata
EC Number
  • 204-066-3
PubChem CID
  • 8255
RTECS number
  • UD0890000
UNII
  • QA2LMR467H checkY
UN number 1055
In Liquefied petroleum gas: 1075
CompTox Dashboard (EPA)
  • DTXSID9020748 Edit this at Wikidata
InChI
  • 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]
Chemical formula
 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
Hazards[2]
GHS labelling:
Flam. Gas 1Press. Gas
Danger
H220
P210, P377, P381, P403
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 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
Autoignition
temperature
 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).
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Infobox references
Chemical compound

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]

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

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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