Isobutylene (or 2-methylpropene) is a
hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ...
with the
chemical formula
In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbol ...
. 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, an ...
(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
Catalysis () is the process of increasing the 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 catalyst recyc ...
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. At ...
of
isobutane (Catofin or similar processes).
[.] Gasoline additives
methyl tert-butyl ether
Methyl ''tertiary''-butyl ether (MTBE), also known as methyl tert-butyl ether and ''tert''-butyl methyl ether, is an organic compound with a structural formula (CH3)3COCH3. MTBE is a volatile, flammable, and colorless liquid that is sparingly sol ...
(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 ethan ...
(ETBE), respectively, are produced by reacting
methanol or
ethanol
Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a ...
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
In organic chemistry, ethenolysis is a chemical process in which internal olefins are degraded using ethylene () as the reagent. The reaction is an example of cross metathesis. The utility of the reaction is driven by the low cost of ethylen ...
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 by ...
:
:
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
In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many fo ...
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
phenol
Phenol (also called carbolic acid) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile. The molecule consists of a phenyl group () bonded to a hydroxy group (). Mildly acidic, it ...
s with isobutylene.
''tert''-Butylamine is produced commercially by amination of isobutylene using
zeolite
Zeolites are microporous, crystalline aluminosilicate materials commonly used as commercial adsorbents and catalysts. They mainly consist of silicon, aluminium, oxygen, and have the general formula ･y where is either a metal ion or H+. These p ...
catalyst
Catalysis () is the process of increasing the 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 catalyst recyc ...
s:
:
NH3 + CH2=C(CH3)2 -> H2NC(CH3)3
Safety
Isobutylene is a highly flammable gas.
See also
*
Butyl rubber
*
Polythene
*
Polybutene
References
External links
*
*
{{Hydrocarbons
Alkenes