Isobutanol

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.

History and occurrence

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

In 1852 Charles Adolphe Wurtz subjected such alcohols to fractional distillation and identified in some of them a butylic alcohol boiling at around 108°C. Its structure was initially unclear, with some chemists believing it corresponded to butyric acid, but theoretical considerations indicated that normal butanol should have a higher boiling point, and in 1867 Emil Erlenmeyer and independently Vladimir Markovnikov determined its actual structure by proving its oxidation product to be isobutyric acid.

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 → CH₃CH₂CH₂CHO
The 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..

Laboratory synthesis

Propanol and methanol can be reacted to produce isobutyl alcohol via Guerbet condensation.

Biosynthesis of isobutanol

''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:
:(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. Isobutanol is also a component of some biofuels.

Safety and regulation

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

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

References

External links

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Alcohol solvents
Primary alcohols
GABAA receptor positive allosteric modulators
Sedatives
Hypnotics
Alkanols
Isobutyl compounds