Isobutylene


Isobutylene is a hydrocarbon of industrial significance. It is a four-carbon branched alkene, one of the four isomers of butylene. At standard temperature and pressure it is a colourless flammable gas but not highly flammable.

Uses

Isobutylene is used as an intermediate in the production of a variety of products. By reaction with methanol and ethanol, it is a precursor to the gasoline oxygenates methyl tert-butyl ether and ethyl tert-butyl ether, respectively. Alkylation with butane produces isooctane, another fuel additive. Isobutylene is also used in the production of methacrolein. Polymerization of isobutylene produces butyl rubber. Antioxidants such as butylated hydroxytoluene and butylated hydroxyanisole are produced by Friedel-Crafts alkylation of phenols using isobutylene.
tert-Butylamine is produced commercially by amination of isobutylene using zeolite catalysts:

Manufacture

Polymer and chemical grade isobutylene is typically obtained by dehydrating tertiary butyl alcohol or catalytic dehydrogenation of isobutane. Gasoline oxygenates MTBE and ETBE 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 the much higher boiling resulting alcohols.

By-product

In the ethenolysis of diisobutylene to prepare neohexene, isobutylene is a byproduct:

Safety

Isobutylene is a highly flammable gas and presents an explosion danger. Usually stored as a compressed, liquefied gas, if released it may produce an oxygen-deficient atmosphere that presents an asphyxiation hazard.