Isobutylene (or 2-methylpropene) is a
hydrocarbon with the
chemical formula . It is a four-carbon branched
alkene
In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond.
Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, a ...
(olefin), one of the four
isomers of butylene. It is a colorless flammable gas, and is of considerable industrial value.
Production
Polymer and chemical grade isobutylene is typically obtained by dehydrating
tertiary butyl alcohol (TBA) or
catalytic dehydrogenation
In chemistry, dehydrogenation is a chemical reaction that involves the removal of hydrogen, usually from an organic molecule. It is the reverse of hydrogenation. Dehydrogenation is important, both as a useful reaction and a serious problem. A ...
of
isobutane (Catofin or similar processes).
[.] Gasoline additives
methyl tert-butyl ether (MTBE) and
ethyl tert-butyl ether
Ethyl ''tertiary''-butyl ether (ETBE), also known as ethyl ''tert''-butyl ether, is commonly used as an oxygenate gasoline additive in the production of gasoline from crude oil. ETBE offers equal or greater air quality benefits than ethanol ...
(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
Neohexene is the hydrocarbon compound with the chemical formula . It is a colorless liquid, with properties similar to other hexenes. It is a precursor to commercial synthetic musk perfumes.
Preparation and reactions
Neohexene is prepared b ...
:
:
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
Methacrolein, or methacrylaldehyde, is an unsaturated aldehyde. It is a clear, colorless, flammable liquid.
Methacrolein is one of two major products resulting from the reaction of isoprene with OH in the atmosphere, the other product being m ...
.
Polymerization of isobutylene produces
butyl rubber
Butyl rubber, sometimes just called "butyl", is a synthetic rubber, a copolymer of isobutylene with isoprene. The abbreviation IIR stands for isobutylene isoprene rubber. Polyisobutylene, also known as "PIB" or polyisobutene, (C4H8)n, is the homo ...
(polyisobutylene or PIB). Antioxidants such as
butylated hydroxytoluene
Butylated hydroxytoluene (BHT), also known as dibutylhydroxytoluene, is a lipophilic organic compound, chemically a derivative of phenol, that is useful for its antioxidant properties. BHT is widely used to prevent free radical-mediated oxidation ...
(BHT) and
butylated hydroxyanisole
Butylated hydroxyanisole (BHA) is a synthetic, waxy, solid petrochemical. Its antioxidant properties have caused it to be widely used as a preservative in food, food packaging, animal feed, cosmetics, pharmaceuticals, rubber, and petroleum produc ...
(BHA) are produced by
Friedel-Crafts alkylation of
phenols with isobutylene.
''tert''-Butylamine is produced commercially by amination of isobutylene using
zeolite catalyst
Catalysis () is the process of increasing the reaction rate, rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the ...
s:
:
NH3 + CH2=C(CH3)2 -> H2NC(CH3)3
Safety
Isobutylene is a highly flammable gas.
See also
*
Butyl rubber
Butyl rubber, sometimes just called "butyl", is a synthetic rubber, a copolymer of isobutylene with isoprene. The abbreviation IIR stands for isobutylene isoprene rubber. Polyisobutylene, also known as "PIB" or polyisobutene, (C4H8)n, is the homo ...
*
Polythene
Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging (plastic bags, plastic films, geomembranes and containers including bot ...
*
Polybutene
References
External links
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{{Hydrocarbons
Alkenes