Isobutanol Explained

Isobutanol (IUPAC nomenclature: 2-methylpropan-1-ol) is an organic compound with the formula (CH₃)₂CHCH₂OH (sometimes represented as i-BuOH). This colorless, flammable liquid with a characteristic smell is mainly used as a solvent either directly or as its esters. Its isomers are 1-butanol, 2-butanol, and tert-butanol, all of which are important industrially.

Occurrence

Fusel alcohols including isobutanol are grain fermentation byproducts. Therefore, trace amounts of isobutanol may be present in many alcoholic beverages.

Production

Isobutanol is produced by the carbonylation of propylene. Two methods are practiced industrially, hydroformylation is more common and generates a mixture of isobutyraldehyde and butyraldehyde:

CH₃CH=CH₂ + CO + H₂ → CH₃CH₂CH₂CHOThe reaction is catalyzed by cobalt or rhodium complexes. The resulting aldehydes are hydrogenated to the alcohols, which are then separated. In Reppe carbonylation, the same products are obtained, but the hydrogenation is effected by the water-gas shift reaction.^[1]

Laboratory synthesis

Propanol and methanol can be reacted to produce isobutyl alcohol via Guerbet condensation.^[2]

Biosynthesis of isobutanol

See main article: Butanol fuel. E. coli as well as several other organisms has been genetically modified to produce C4 alcohols from glucose, including isobutanol, 1-butanol, 2-methyl-1-butanol, 3-methyl-1-butanol, and 2-phenylethanol. The host's highly active amino acid biosynthetic pathway is shifted to alcohol production. α-Ketoisovalerate, derived from valine, is prone to decarboxylation to give isobutyraldehyde, which is susceptible to reduction to the alcohol:^[3]

(CH₃)₂CHC(O)CO₂H → (CH₃)₂CHCHO + CO₂

(CH₃)₂CHCHO + NADH + H⁺ → (CH₃)₂CHCH₂OH + NAD⁺

Applications

The uses of isobutanol and 1-Butanol are similar. They are often used interchangeably. The main applications are as varnishes and precursors to esters, which are useful solvents, e.g. isobutyl acetate. Isobutyl esters of phthalic, adipic, and related dicarboxylic acids are common plasticizers.^[1] Isobutanol is also a component of some biofuels.^[4]

Safety and regulation

Isobutanol is one of the least toxic of the butanols with an of 2460 mg/kg (rat, oral).^[1]

In March 2009, the Government of Canada announced a ban on isobutanol use in cosmetics.^[5]

Notes and References

1. .
2. Guerbet condensation of methanol with n-propanol to isobutyl alcohol over heterogeneous copper chromite/Mg–Al mixed oxides catalysts. 2004-09-01. Molecular Catalysis. 220. 2. 215–220. The synthesis of isobutyl alcohol from methanol (MeOH) and n-propanol (PrOH) through the Guerbet condensation has been studied [. . .] using catalytic system of copper chromite and Mg-Al mixed oxides.. 10.1016/j.molcata.2004.05.034. Carlo. Carlini. Cristina. Flego. Mario. Marchionna.
3. Non-fermentative pathways for synthesis of branched-chain higher alcohols as biofuels. Nature. 86–89. 451. 7174. 10.1038/nature06450. Shota. Atsumi. Taizo. Hanai. James C.. Liao. 18172501. January 2008. 2008Natur.451...86A. 4413113.
4. Peralta-Yahya. Pamela P.. Zhang, Fuzhong. del Cardayre, Stephen B.. Keasling, Jay D.. Microbial engineering for the production of advanced biofuels. Nature. 15 August 2012. 488. 7411. 320–328. 10.1038/nature11478. 22895337. 2012Natur.488..320P. 4423203.
5. .