Isobutylene

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
CAS Number	115-11-7 ;
3D model (JSmol)	Interactive image;
ChEBI	CHEBI:43907 ;
ChemSpider	7957 ;
ECHA InfoCard	100.003.697
EC Number	204-066-3;
PubChem CID	8255;
RTECS number	UD0890000;
UNII	QA2LMR467H ;
UN number	1055; In Liquefied petroleum gas: 1075
CompTox Dashboard (EPA)	DTXSID9020748 ;
	InChI InChI=1S/C4H8/c1-4(2)3/h1H2,2-3H3 Key: VQTUBCCKSQIDNK-UHFFFAOYSA-N ; InChI=1/C4H8/c1-4(2)3/h1H2,2-3H3;
	SMILES 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)
Magnetic susceptibility (χ)	-44.4·10−6 cm3/mol
Hazards[2]
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H220
Precautionary statements	P210, P377, P381, P403
NFPA 704 (fire diamond)	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). verify (what is ?) Infobox references

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 or

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

{\ce {(CH3)3C-CH=C(CH3)2}}+{\color {red}{\ce {CH2=CH2}}}\longrightarrow {\ce {(CH3)3C-CH=}}{\color {red}{\ce {CH2}}}+{\ce {(CH3)2C=}}{\color {red}{\ce {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]

{\ce {NH3 + CH2=C(CH3)2 -> H2NC(CH3)3}}

Safety

Isobutylene is a highly flammable gas.

References

The Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals (11th ed.), Merck, 1989, ISBN 091191028X, 5024.
Isobutene, International Chemical Safety Card 1027, Geneva: International Programme on Chemical Safety, April 2000
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.
Olah, George A.; Molnár, Árpád (May 2003), Hydrocarbon Chemistry, Wiley-Interscience, ISBN 978-0-471-41782-8.
Lionel Delaude; Alfred F. Noels. "Metathesis". Kirk-Othmer Encyclopedia of Chemical Technology. Wiley.
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

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[1] The Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals (11th ed.), Merck, 1989, ISBN 091191028X, 5024.

[ICSC-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 (May 2003), Hydrocarbon Chemistry, Wiley-Interscience, ISBN 978-0-471-41782-8.

[KO-5] Lionel Delaude; Alfred F. Noels. "Metathesis". Kirk-Othmer Encyclopedia of Chemical Technology. Wiley.

[Ullmann-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.