What Is Isobutylene?
Isobutene is a hydrocarbon with the chemical formula C4H8 and four carbon atoms in a branched form.
It is also called isobuthylene or 2-methylpropene. It is one of the three isomers of butene and is the most chemically reactive of the three. It is therefore one of the most important raw materials in petrochemistry.
Isobutylene is extremely flammable and creates an explosive mixture with air. It is classified as a hazardous material and must be handled and managed with care.
Uses of Isobutylene
Isobutylene is widely used as a synthetic intermediate in the petrochemical industry.
When isobutylene is added to methanol or ethanol, methyl tert-butyl ether and ethyl tert-butyl ether, which are used as gasoline additives, can be produced. Alkylation of isobutylene yields Isooctane, which is added to gasoline.
Isobutylene is also used in the manufacture of synthetic resins, synthetic rubbers, and various plastics.
Properties of Isobutylene
Isobutylene has a melting point of -140.3°C and a boiling point of -6.9°C. It exists as a colorless gas at room temperature and pressure. It is highly flammable and explosive. Its ignition point is 465°C. It is insoluble in water.
Structure of Isobutylene
Isobutylene is composed of two methyl groups attached to one carbon atom of ethylene. The specific formula is CH2=C(CH3)2. Its molar mass is 56.11 g/mol and its density is 0.5879 g/cm3.
Structural isomers of isobutylene include 1-butene and 2-butene; 2-butene has geometric isomers, cis-2-butene and trans-2-butene. Isobutylene can be separated by physical or chemical methods due to its small molecular size.
Other Information on Isobutylene
1. Production of Isobutylene
Butenes are produced by catalytic cracking as a byproduct of ethylene and propylene, producing C4 fractions with a total weight of less than 10%. After the recovery of butadiene, the main fraction is isobutylene, which is around 40%. The remainder is 1-butene at more than 20 percent and 2-butene at 20 percent, with a mixture of n-butane and isobutane. However, the formation ratio of the components changes with the adjustment of catalytic cracking.
2. Synthesis of Isobutylene
Isobutylene can be isolated by reaction with sulfuric acid in a petroleum refinery stream; it can also be produced by dehydration of tert-butyl alcohol or catalytic dehydrogenation of isobutane. It can also be synthesized from acetone, cellulose, and xylose.
Isobutene is also produced as a by-product of the ethenolysis of diisobutylene during the synthesis of neohexene.
3. Reactions of Isobutylene
Isobutylene can be used as a raw material for methacrolein. When methanol or ethanol is added to isobutylene, methyl tert-butyl ether or ethyl tert-butyl ether is formed. Commercially, tert-butylamine is produced by zeolite-catalyzed amination of isobutylene.
Isooctane can be synthesized by alkylation of isobutylene. The Friedel-Crafts reaction with phenol or 4-methoxyphenol yields dibutylhydroxytoluene and butylhydroxyanisole from isobutylene.
Polyisobutylene can be produced by polymerization of isobutylene. Butyl rubber is a copolymer of isoprene and isobutylene.