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Acetylacetone

Acetylacetone
Skeletal structures of both tautomers
Ball-and-stick model of the enol tautomer
Ball-and-stick model of the keto tautomer
Names
Preferred IUPAC name
Pentane-2,4-dione
Other names
Hacac
Identifiers
123-54-6 YesY
3D model (Jmol) Interactive image
Interactive image
ChEBI CHEBI:14750 YesY
ChEMBL ChEMBL191625 YesY
ChemSpider 29001 YesY
ECHA InfoCard 100.004.214
KEGG C15499 YesY
UNII 46R950BP4J YesY
Properties
C5H8O2
Molar mass 100.12 g·mol−1
Density 0.975 g/mL
Melting point −23 °C (−9 °F; 250 K)
Boiling point 140 °C (284 °F; 413 K)
16 g/100 mL
-54.88·10−6 cm3/mol
Hazards
Harmful (Xn)
R-phrases R10, R22
S-phrases (S2), S21, S23, S24/25
NFPA 704
Flammability code 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g., diesel fuel Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Flash point 34 °C (93 °F; 307 K)
340 °C (644 °F; 613 K)
Explosive limits 2.4–11.6%
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
YesY  (what is YesYN ?)
Infobox references

Acetylacetone is an organic compound that exists in two tautomeric forms that interconvert rapidly and are treated as a single compound in most applications. Although the compound is formally named as the diketone form, pentane-2,4-dione, the enol form forms a substantial component of the material and is actually the favored form in many solvents. It is a colourless liquid that is a precursor to acetylacetonate (acac), a common bidentate ligand. It is also a building block for the synthesis of heterocyclic compounds.

The keto and enol forms of acetylacetone coexist in solution; these forms are tautomers. The enol form has C2vsymmetry, meaning the hydrogen atom is shared equally between the two oxygen atoms. In the gas phase, the equilibrium constant, Kketo→enol, is 11.7, favoring the enol form. The two tautomeric forms can easily be distinguished by NMR spectroscopy, IR spectroscopy, and other methods.

The equilibrium constant tends to remain high in nonpolar solvents; the keto form becomes more favorable in polar, hydrogen-bonding solvents, such as water. The enol form is a vinylogous analogue of a carboxylic acid.

Acetylacetone is a weak acid:

IUPAC recommended pKa values for this equilibrium in aqueous solution at 25 °C are 8.99 ± 0.04 (I = 0), 8.83 ± 0.02 (I = 0.1 M NaClO4) and 9.00 ± 0.03 (I = 1.0 M NaClO4; I = Ionic strength). Values for mixed solvents are available. Very strong bases, such as organolithium compounds, will deprotonate acetylacetone twice. The resulting dilithio species can then be alkylated at C-1.


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