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Not to be confused with Acetone.
Other names
Acetyl methyl carbinol
513-86-0 YesY
ChEBI CHEBI:15688 YesY
ChemSpider 21105851 YesY
EC number 208-174-1
Jmol-3D images Image
KEGG C01769 YesY
PubChem 179
RTECS number EL8790000
Molar mass 88.11 g·mol−1
Appearance slightly yellow liquid or crystals
Odor bland, yogurt-like
Density 1.012 g/cm³
Melting point 15 °C (59 °F; 288 K)
Boiling point 148 °C (298 °F; 421 K)
Solubility soluble in alcohol
slightly soluble in ether, petroleum ether
miscible in propylene glycol
insoluble in vegetable oil
log P -0.36
Acidity (pKa) 13.72
Flash point 41 °C (106 °F; 314 K)
> 5000 mg/kg (rat, oral)
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Acetoin, also known as 3-hydroxybutanone or acetyl methyl carbinol, with the molecular formula is C4H8O2, is a colorless or pale yellow to green yellow liquid with a pleasant, buttery odor. Acetoin is a chiral molecule. The form produced by bacteria is (R)-acetoin.[1]

Production in bacteria[edit]

Acetoin is a neutral, four-carbon molecule used as an external energy store by a number of fermentive bacteria. It is produced by the decarboxylation of alpha-acetolactate, a common precursor in the biosynthesis of branched-chain amino acids. Owing to its neutral nature, production and excretion of acetoin during exponential growth prevents overacidification of the cytoplasm and the surrounding medium that would result from accumulation of acidic metabolic products, such as acetic acid and citric acid. Once superior carbon sources are exhausted, and the culture enters stationary phase, acetoin can be used to maintain the culture density.[2] The conversion of acetoin into acetyl-CoA is catalysed by the acetoin dehydrogenase complex, following a mechanism largely analogous to the pyruvate dehydrogenase complex; however, as acetoin is not a 2-oxoacid, it does not undergo decarboxylation by the E1 enzyme; instead, a molecule of acetaldehyde is released.[3] In some bacteria, acetoin can also be reduced to 2,3-butanediol by acetoin reductase/2,3-butanediol dehydrogenase.

The Voges-Proskauer test is a commonly used microbiological test for acetoin production.[4]

In food products[edit]

Acetoin, along with diacetyl, is one of the compounds giving butter its characteristic flavor. Because of this, manufacturers of partially hydrogenated oils typically add acetoin and diacetyl (along with beta carotene for the yellow color) to the final product, which would otherwise be tasteless.[5]

Acetoin is used as a food flavoring (in baked goods) and a fragrance. It can be found in apples, butter, yogurt, asparagus, black currants, blackberry, wheat, broccoli, brussels sprouts, cantaloupe.

Cigarette additive[edit]

In a 1994 report released by five top cigarette companies, acetoin was listed as one of the 599 additives to cigarettes. [6]


  1. ^ Albert Gossauer: Struktur und Reaktivität der Biomoleküle, Verlag Helvetica Chimica Acta, Zürich, 2006, Seite 285, ISBN 978-3-906390-29-1.
  2. ^ Xiao, Z. and Xu, P. (2007). "Acetoin metabolism in bacteria". Crit Rev Microbiol. 33 (2): 127–140. doi:10.1080/10408410701364604. PMID 17558661. 
  3. ^ Oppermann, F.B. and Steinbuchel, A. (1994). "Identification and molecular characterization of the aco genes encoding the Pelobacter carbinolicus acetoin dehydrogenase enzyme system". J Bacteriol. 176 (2): 469–485. PMC 205071. PMID 8110297. 
  4. ^ Speckman, R.A. and Collins, E.B. (1982). "Specificity of the Westerfeld adaptation of the Voges-Proskauer test". Appl Environ Microbiol. 44 (1): 40–43. PMC 241965. PMID 6751225. 
  5. ^ Pavia et al., Introduction to Organic Laboratory Techniques, 4th ed., ISBN 978-0-495-28069-9
  6. ^ "What's in a cigarette?". Archived from the original on 23 May 2006. Retrieved 2006-05-31.