Title: Diacetyl
CAS Registry Number: 431-03-8
CAS Name: 2,3-Butanedione
Additional Names: biacetyl; dimethyl diketone; dimethylglyoxal; 2,3-diketobutane
Molecular Formula: C4H6O2
Molecular Weight: 86.09
Percent Composition: C 55.81%, H 7.02%, O 37.17%
Line Formula: CH3COCOCH3
Literature References: Found in bay and other oils; also in butter. Made from methyl ethyl ketone by converting to the isonitroso compd and then decomposing to diacetyl by hydrolysis with HCl; by special fermentation of glucose via methylacetylcarbinol: Suomalainen, Jännes, Nature 157, 336 (1946). Toxicity study: P. M. Jenner et al., Food Cosmet. Toxicol. 2, 327 (1964).
Properties: Yellowish-green liq; quinone odor; the vapors have a Cl-like odor. d1515 0.990. bp 88°. nD18 1.3933. Sol in ~4 parts water; misc with alcohol, ether. LD50 orally in rats: 1580 mg/kg (Jenner).
Boiling point: bp 88°
Index of refraction: nD18 1.3933
Density: d1515 0.990
Toxicity data: LD50 orally in rats: 1580 mg/kg (Jenner)
Use: Carrier of aroma of butter, vinegar, coffee, and other foods.
Diacetyldihydromorphine Diacetylmorphine Diafenthiuron Dialifor Diallate

Structural formula
Ball-and-stick model
CAS number 431-03-8 YesY
PubChem 650
ChemSpider 630 YesY
KEGG C00741 YesY
ChEBI CHEBI:16583 YesY
Jmol-3D images Image 1
Molecular formula C4H6O2
Molar mass 86.0892 g/mol
Appearance Yellowish green liquid
Density 0.990 g/mL at 15 °C
Melting point −2 to −4 °C
Boiling point 88 °C
Solubility in water Soluble in 4 parts
MSDS External MSDS
R-phrases R10 R22 R36 R37 R38
S-phrases S9 S16 S33
Main hazards Harmful, flammable
 YesY (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

Diacetyl (IUPAC systematic name: butanedione or butane-2,3-dione) is an organic compound with the chemical formula (CH3CO)2. It is a volatile, colourless liquid with an intensely buttery flavor. It is a vicinal diketone (two C=O groups, side-by-side) with the molecular formula C4H6O2. Diacetyl occurs naturally in alcoholic beverages and is added to some foods to impart its buttery flavor.

A distinctive feature of diacetyl (and other 1,2-diketones) is the long C-C bond linking the carbonyl centers. This bond distance is about 1.54 Å, compared to 1.45 Å for the corresponding C-C bond in 1,3-butadiene. The elongation is attributed to repulsion between the polarized carbonyl carbon centers.[2]