Acetoin

Not to be confused with Acetone.

Acetoin, also known as 3-hydroxybutanone or acetyl methyl carbinol, is an organic compound with the formula CH₃CH(OH)C(O)CH₃. It is a colorless liquid with a pleasant, buttery odor. It is chiral. The form produced by bacteria is (R)-acetoin.^[1]

Acetoin

Names
Preferred IUPAC name 3-Hydroxybutan-2-one
Other names 3-Hydroxybutanone Acetyl methyl carbinol
Identifiers
CAS Number	513-86-0 (R/S) Y 53584-56-8 (R) Y 78183-56-9 (S) Y
3D model (JSmol)	Interactive image (R): Interactive image (S): Interactive image
ChEBI	CHEBI:15688 Y CHEBI:15686 (R) CHEBI:15687 (S)
ChemSpider	21105851 Y 388445 (R) 394765 (S)
ECHA InfoCard	100.007.432
EC Number	208-174-1
KEGG	C00466 C00810 (R) C01769 (S)
PubChem CID	179 439314 (R) 447765 (S)
RTECS number	EL8790000
UNII	BG4D34CO2H Y
CompTox Dashboard (EPA)	DTXSID0024399
InChI InChI=1S/C4H8O2/c1-3(5)4(2)6/h3,5H,1-2H3 Y Key: ROWKJAVDOGWPAT-UHFFFAOYSA-N Y InChI=1/C4H8O2/c1-3(5)4(2)6/h3,5H,1-2H3 Key: ROWKJAVDOGWPAT-UHFFFAOYAD
SMILES CC(=O)C(C)O (R): CC(=O)[C@@H](C)O (S): CC(=O)[C@H](C)O
Properties
Chemical formula	C4H8O2
Molar mass	88.106 g·mol−1
Appearance	colorless liquid
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 in water	1000 g/L (20 °C)
Solubility in other solvents	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
Chiral rotation ([α]D)	-39.4
Refractive index (nD)	1.4171
Hazards
Flash point	41 °C (106 °F; 314 K)
Lethal dose or concentration (LD, LC):
LD50 (median dose)	> 5000 mg/kg (rat, oral)
Safety data sheet (SDS)	MSDS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Production in bacteria

Acetoin is a neutral, four-carbon molecule used as an external energy store by a number of fermentative 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 over-acidification 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]

Uses

Food ingredients

Acetoin, along with diacetyl, is one of the compounds that gives butter its characteristic flavor. Because of this, manufacturers of partially hydrogenated oils typically add artificial butter flavor – acetoin and diacetyl – (along with beta carotene for the yellow color) to the final product.^[5]

Acetoin can be found in apples, yogurt, asparagus, blackcurrants, blackberries, wheat, broccoli, brussels sprouts, cantaloupes, and maple syrup.^[6][7][8]

Acetoin is used as a food flavoring (in baked goods) and as a fragrance.

Electronic cigarettes

It is used in liquids for electronic cigarettes to give a buttery or caramel flavor.^[9]

See also

• Diacetyl
• Acetylpropionyl

References

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.; Xu, P. (2007). "Acetoin metabolism in bacteria". Crit Rev Microbiol. 33 (2): 127–140. doi:10.1080/10408410701364604. PMID 17558661. S2CID 46151943.
3. Oppermann, F.B.; 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. doi:10.1128/jb.176.2.469-485.1994. PMC 205071. PMID 8110297.
4. Speckman, R.A.; Collins, E.B. (1982). "Specificity of the Westerfeld adaptation of the Voges-Proskauer test". Appl Environ Microbiol. 44 (1): 40–43. Bibcode:1982ApEnM..44...40S. doi:10.1128/aem.44.1.40-43.1982. PMC 241965. PMID 6751225.
5. Pavia et al., Introduction to Organic Laboratory Techniques, 4th ed., ISBN 978-0-495-28069-9
6. "Sampling and Analytical Methods: Acetoin, Diacetyl, 1012". Archived from the original on 2018-06-04.
7. "Allendale Columbia | STEM".
8. "Evaluation of Natural Acetyl Methyl Carbinol|Flavorist". www.fks.com.
9. Committee on the Review of the Health Effects of Electronic Nicotine Delivery Systems, National Academies of Sciences (2018). "Chapter 5: Toxicology of E-Cigarette Constituents". In Eaton, David L.; Kwan, Leslie Y.; Stratton, Kathleen (eds.). Public Health Consequences of E-Cigarettes. National Academies Press. p. 175. ISBN 9780309468343. PMID 29894118.