Isobutanol

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.{{cite journal

Biosynthesis of isobutanol

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: :(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.

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

References

1. {{ICSC-ref. 01. 13. (April 2005.)
2. "Iso-butanol". ChemicalLand21.
3. {{PGCH. 0352
4. {{IDLH. 78831. Isobutyl alcohol
5. [[s:fr:Page:Comptes rendus hebdomadaires des séances de l’Académie des sciences, tome 035, 1852.djvu/314]]
6. (1888). "The chemistry of the hydrocarbons and their derivatives, or Organic chemistry. 1882-1892. 6 v". D. Appleton.
7. "The Quiet Revolution".
8. (2005). "Butanols".
9. (January 2008). "Non-fermentative pathways for synthesis of branched-chain higher alcohols as biofuels". Nature.
10. Peralta-Yahya, Pamela P.. (15 August 2012). "Microbial engineering for the production of advanced biofuels". Nature.
11. (2009-03-16). "Cosmetic Chemicals Banned in Canada". Chem. Eng. News.