From Wikipedia, the free encyclopedia
Jump to navigation Jump to search
Skeletal structures of both tautomers
Ball-and-stick model of the enol tautomer
Ball-and-stick model of the keto tautomer
Preferred IUPAC name
Other names
3D model (JSmol)
ECHA InfoCard 100.004.214
EC Number 204-634-0
RTECS number SA1925000
UN number 2310
Molar mass 100.12 g·mol−1
Density 0.975 g/mL[1]
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
GHS pictograms The flame pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)The skull-and-crossbones pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)The exclamation-mark pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)The health hazard pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)
GHS signal word Danger
H226, H302, H311, H320, H331, H335, H341, H370, H402, H412
P201, P202, P210, P233, P240, P241, P242, P243, P260, P261, P264, P270, P271, P273, P280, P281, P301+312, P302+352, P303+361+353, P304+340, P305+351+338, P307+311, P308+313, P311, P312
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 fuelHealth code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroformReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogenSpecial 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).
☑Y verify (what is ☑Y‹See TfM›☒N ?)
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[2] 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.



Acetylacetone keto-enol tautomerism.svg

The keto and enol forms of acetylacetone coexist in solution; these forms are tautomers. The enol form has C2v symmetry, meaning the hydrogen atom is shared equally between the two oxygen atoms.[3] 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.[4][5]

Solvent Kketo→enol
Gas phase 11.7
Cyclohexane 42
Toluene 10
THF 7.2
Water 0.23

The equilibrium constant tends to remain high in nonpolar solvents; the keto form becomes more favorable in polar, hydrogen-bonding solvents, such as water.[6] The enol form is a vinylogous analogue of a carboxylic acid.

Acid–base properties[edit]

solvent T/°C pKa[7]
40% ethanol/water 30 9.8
70% dioxane/water 28 12.5
80% DMSO/water 25 10.16
DMSO 25 13.41

Acetylacetone is a weak acid:

+ H+

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).[8] 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.


Acetylacetone is prepared industrially by the thermal rearrangement of isopropenyl acetate.[9]

CH2(CH3)COC(O)Me → MeC(O)CH2C(O)Me

Laboratory routes to acetylacetone begin also with acetone. Acetone and acetic anhydride upon the addition of BF3 catalyst:[10]

(CH3CO)2O + CH3C(O)CH3 → CH3C(O)CH2C(O)CH3

A second synthesis involves the base-catalyzed condensation of acetone and ethyl acetate, followed by acidification:[10]

NaOEt + EtO2CCH3 + CH3C(O)CH3 → NaCH3C(O)CHC(O)CH3 + 2 EtOH
NaCH3C(O)CHC(O)CH3 + HCl → CH3C(O)CH2C(O)CH3 + NaCl

Because of the ease of these syntheses, many analogues of acetylacetonates are known. Some examples include C6H5C(O)CH2C(O)C6H5 (dbaH) and (CH3)3CC(O)CH2C(O)CC(CH3)3. Hexafluoroacetylacetonate is also widely used to generate volatile metal complexes.



Acetylacetone is a versatile bifunctional precursor to heterocycles because both keto groups undergo condensation. Hydrazine reacts to produce pyrazoles. Urea gives pyrimidines. Condensation with two aryl- and alkylamines to gives NacNacs, wherein the oxygen atoms in acetylacetone are replaced by NR (R = aryl, alkyl).

Coordination chemistry[edit]

A ball-and-stick model of VO(acac)2

The acetylacetonate anion, acac, forms complexes with many transition metal ions. A general method of synthesis is to react the metal ion with acetylacetone in the presence of a base (B):

MBz + z Hacac ⇌ M(acac)z + z BH

which assists the removal of a proton from acetylacetone and shifts the equilibrium in favour of the complex. Both oxygen atoms bind to the metal to form a six-membered chelate ring. In some cases the chelate effect is so strong that no added base is needed to form the complex. Since the metal complex carries no electrical charge, it is often insoluble in water but soluble in nonpolar organic solvents.


Enzymatic breakdown: The enzyme acetylacetone dioxygenase cleaves the carbon-carbon bond of acetylacetone, producing acetate and 2-oxopropanal. The enzyme is iron(II)-dependent, but it has been proven to bind to zinc as well. Acetylacetone degradation has been characterized in the bacterium Acinetobacter johnsonii.[11]

C5H8O2 + O2 → C2H4O2 + C3H4O2


  1. ^ "05581: Acetylacetone". Sigma-Aldrich.
  2. ^ O'Brien, Brian. "Co(tfa)3 & Co(acac)3 handout" (PDF). Gustavus Adolphus College.
  3. ^ Caminati, W.; Grabow, J.-U. (2006). "The C2v Structure of Enolic Acetylacetone". J. Am. Chem. Soc. 128 (3): 854–857. doi:10.1021/ja055333g. PMID 16417375.
  4. ^ Manbeck, Kimberly A.; Boaz, Nicholas C.; Bair, Nathaniel C.; Sanders, Allix M. S.; Marsh, Anderson L. (2011). "Substituent Effects on Keto–Enol Equilibria Using NMR Spectroscopy". J. Chem. Educ. 88 (10): 1444–1445. doi:10.1021/ed1010932.
  5. ^ Yoshida, Z.; Ogoshi, H.; Tokumitsu, T. (1970). "Intramolecular hydrogen bond in enol form of 3-substituted-2,4-pentanedione". Tetrahedron. 26: 5691–5697. doi:10.1016/0040-4020(70)80005-9.
  6. ^ Reichardt, Christian (2003). Solvents and Solvent Effects in Organic Chemistry (3rd ed.). Wiley-VCH. ISBN 3-527-30618-8.
  7. ^ IUPAC SC-Database A comprehensive database of published data on equilibrium constants of metal complexes and ligands
  8. ^ Stary, J.; Liljenzin, J. O. (1982). "Critical evaluation of equilibrium constants involving acetylacetone and its metal chelates" (PDF). Pure and Applied Chemistry. 54 (12): 2557–2592. doi:10.1351/pac198254122557.
  9. ^ Siegel, Hardo; Eggersdorfer, Manfred (2002). "Ketones". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a15_077.
  10. ^ a b C. E. Denoon, Jr. "Acetylacetone". Organic Syntheses.; Collective Volume, 3, p. 16
  11. ^ Straganz, G.D.; Glieder, A.; Brecker, L.; Ribbons, D.W.; Steiner, W. (2003). "Acetylacetone-cleaving enzyme Dke1: a novel C–C-bond-cleaving enzyme from Acinetobacter johnsonii". Biochem. J. 369 (3): 573–581. doi:10.1042/BJ20021047. PMC 1223103. PMID 12379146.

External links[edit]