What Is Butene?
Butene is an unsaturated hydrocarbon with one double bond, whose molecular formula is represented by C4H8.
There are three isomers: 1-butene, 2-butene, and isobutene; two types of 2-butene exist: CIS-2-butene and trans-2-butene. Both are colorless gases with an odor characteristic of olefin gas and have a molecular weight of 56.10 g/mol.
Butene is present in the C4 fraction of the naphtha cracking process or the by-product C4 fraction of oil catalytic cracking and can be separated by distillation, among others. 1-butene and 2-butene are often used as liquefied petroleum gas in a mixed form.
Uses of Butene
The main uses of isomers of butene are as follows
- 1-Butene
It has a highly reactive double bond and is an important raw material in the petrochemical industry. It is used as a liquefied petroleum gas for fuel and as a synthetic raw material for the production of butyl alcohol, ethyl methyl ketone, and pentanol, which are used to make butyl alcohol and butadiene. - 2-Butene
Industrially, it is used as an n-butene mixture, not separated from 1-butene. - Isobutene
In addition to being used as a raw material for the production of isooctane and polymerized gasoline, isobutene is also used as a raw material for the production of synthetic rubber and alkyl halides.
Properties of Butene
1-butene has a melting point of -185.3°C, a boiling point of -6.3°C, and an ignition point of 384°C. It is soluble in ethanol, benzene, and diethyl ether.
CIS-2-butene has a melting point of -138.9°C and a boiling point of 3.7°C. Trans-2-butene has a melting point of -105.5°C and a boiling point of 0.9°C. Due to their very close boiling points, isomers are difficult to separate by distillation but often do not need to be separated because they exhibit similar reactivity. Typically, 2-butene is commercially available as a mixture of 70% cis and 30% trans.
Isobutene has a melting point of -140.3°C and a boiling point of -6.9°C.
Butene Structure
1-butene is a linear α-alkene. Its differential formula is CH3CH2CH=CH2 and its density is 0.62 g/cm3.
2-butene is the simplest alkene with geometrical isomerism and is represented by the differential formula CH3CH=CHCH3. cis-2-butene at 3.7°C has a density of 0.641 g/cm3 and trans-2-butene at 0.9°C has a density of 0.626 g/cm3. Cis-2-butene is also called cis-β-butylene and trans-2-butene is also called trans-β-butylene.
Isobutene has a structure in which two methyl groups are bonded to one carbon atom of ethylene. Its specific formula is CH2=C(CH3)2 and its density is 0.5879 g/cm3.
Other Information on Butene
1. Synthesis of Butene
Separation of crude C4 fractions yields a mixture of 1-butene and 2-butene. Dimerization of ethylene produces only terminal alkenes. It can be purified to high purity by distillation.
Isobutene can be isolated by reaction with sulfuric acid in the petroleum refining stream. It can usually be produced by catalytic dehydrogenation of isobutane. It can also be produced from acetone, cellulose, and xylose. Isobutene is also produced as a byproduct of the ethenolysis of diisobutylene during the synthesis of neohexene.
2. Butene Reaction
1-butene is easily polymerized to form polybutene. It is a raw material for the production of linear polyethylene and can be used as a precursor for polypropylene resin, methyl ethyl ketone, and epoxy butane.
Butadiene can be produced from 2-butene. Hydration reaction yields 2-butanol, which is oxidized to methyl ethyl ketone.
Isobutene is a raw material for methacrolein. The addition of methanol or ethanol to isobutene yields methyl tert-butyl ether or ethyl tert-butyl ether. Commercially tert-butylamine is also produced by zeolite-catalyzed amination of isobutylene. Polyisobutylene is produced when isobutene is polymerized, and isooctane can be synthesized by alkylation of isobutene. Friedel-Crafts reactions with phenol and 4-methoxyphenol yield dibutylhydroxytoluene and butylhydroxyanisole from isobutene.