Acetylacetone

Acetylacetone is an organic compound with the chemical formula CH3COCH2COCH3. It is a colorless liquid, classified as a 1,3-diketone. It exists in equilibrium with a tautomer CH3C(O)CH=(OH)CH3. These tautomers interconvert so rapidly under most conditions that they are treated as a single compound in most applications.[2] It is a colorless liquid that is a precursor to acetylacetonate anion (commonly abbreviated acac−), a bidentate ligand. It is also a building block for the synthesis of heterocyclic compounds.

Acetylacetone
Ball-and-stick model of the enol tautomer
Ball-and-stick model of the keto tautomer
Space-filling model of the enol tautomer
Space-filling model of the keto tautomer
Names
Preferred IUPAC name
Pentane-2,4-dione
Other names
  • Hacac
  • 2,4-pentanedione
Identifiers
3D model (JSmol)
Beilstein Reference
 741937
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.004.214
EC Number
  • 204-634-0
Gmelin Reference
 2537
KEGG
RTECS number
  • SA1925000
UNII
UN number 2310
CompTox Dashboard (EPA)
  • InChI=1S/C5H8O2/c1-4(6)3-5(2)7/h3H2,1-2H3 Y
    Key: YRKCREAYFQTBPV-UHFFFAOYSA-N Y
  • InChI=1/C5H8O2/c1-4(6)3-5(2)7/h3H2,1-2H3
    Key: YRKCREAYFQTBPV-UHFFFAOYAO
  • O=C(C)CC(=O)C
  • CC(=O)CC(=O)C
  • Enol form: CC(O)=CC(=O)C
Properties
C5H8O2
Molar mass 100.117 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
Hazards
GHS labelling:
Danger
Hazard statements
 H226, H302, H311, H320, H331, H335, H341, H370, H412
Precautionary statements
 P201, P202, P210, P233, P240, P241, P242, P243, P260, P261, P264, P270, P271, P273, P280, P281, P301+P312, P302+P352, P303+P361+P353, P304+P340, P305+P351+P338, P307+P311, P308+P313, P311, P312, P321, P322, P330, P337+P313, P361, P363, P370+P378, P403+P233, P403+P235, P405, P501
NFPA 704 (fire diamond)
2
2
0
Flash point 34 °C (93 °F; 307 K)
Autoignition
temperature
 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 YN ?)
Infobox references

Properties

Tautomerism
SolventKketo→enol
Gas phase11.7
Cyclohexane42
Toluene10
THF7.2
CDCl3[3]5.7
DMSO2
Water0.23

The keto and enol tautomers of acetylacetone coexist in solution. The enol form has C2v symmetry, meaning the hydrogen atom is shared equally between the two oxygen atoms.[4] In the gas phase, the equilibrium constant, Kketo→enol, is 11.7, favoring the enol form. The two tautomeric forms can be distinguished by NMR spectroscopy, IR spectroscopy and other methods.[5][6]

The equilibrium constant tends to be high in nonpolar solvents; when k = >1, the enol form is favoured. The keto form becomes more favourable in polar, hydrogen-bonding solvents, such as water.[7] The enol form is a vinylogous analogue of a carboxylic acid.

Acid–base properties
solventT/°CpKa[8]
40% ethanol/water309.8
70% dioxane/water2812.5
80% DMSO/water2510.16
DMSO2513.41

Acetylacetone is a weak acid:

C5H8O2 ⇌ C5H7O−2 + 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).[9] Values for mixed solvents are available. Very strong bases, such as organolithium compounds, will deprotonate acetylacetone twice. The resulting dilithium species can then be alkylated at C-1.

Preparation

Acetylacetone is prepared industrially by the thermal rearrangement of isopropenyl acetate.[10]

Laboratory routes to acetylacetone also begin with acetone. Acetone and acetic anhydride upon the addition of boron trifluoride (BF3) catalyst:[11]

(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:[11]

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 benzoylacetone, dibenzoylmethane (dbaH) and tert-butyl analogue tetramethyl-3,5-heptanedione. Trifluoroacetylacetone and hexafluoroacetylacetonate are also used to generate volatile metal complexes.

Reactions

Condensations

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

Sodium acetylacetonate, Na(acac), is the precursor to many acetylacetonate complexes. A general method of synthesis is to treat a metal salt with acetylacetone in the presence of a base:[12]

MBz + z Hacac ⇌ M(acac)z + z BH

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.

Biodegradation

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.[13]

C5H8O2 + O2 → C2H4O2 + C3H4O2

References
  1. "05581: Acetylacetone". Sigma-Aldrich.
  2. Thomas M. Harris (2001). "2,4-Pentanedione". 2,4‐Pentanedione. e-EROS Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rp030. ISBN 0471936235.
  3. Smith, Kyle T.; Young, Sherri C.; DeBlasio, James W.; Hamann, Christian S. (12 April 2016). "Measuring Structural and Electronic Effects on Keto–Enol Equilibrium in 1,3-Dicarbonyl Compounds". Journal of Chemical Education. 93 (4): 790–794. doi:10.1021/acs.jchemed.5b00170.
  4. Caminati, W.; Grabow, J.-U. (2006). "The C2v Structure of Enolic Acetylacetone". Journal of the American Chemical Society. 128 (3): 854–857. doi:10.1021/ja055333g. PMID 16417375.
  5. 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". Journal of Chemical Education. 88 (10): 1444–1445. Bibcode:2011JChEd..88.1444M. doi:10.1021/ed1010932.
  6. Yoshida, Z.; Ogoshi, H.; Tokumitsu, T. (1970). "Intramolecular hydrogen bond in enol form of 3-substituted-2,4-pentanedione". Tetrahedron. 26 (24): 5691–5697. doi:10.1016/0040-4020(70)80005-9.
  7. Reichardt, Christian (2003). Solvents and Solvent Effects in Organic Chemistry (3rd ed.). Wiley-VCH. ISBN 3-527-30618-8.
  8. IUPAC SC-Database Archived 2017-06-19 at the Wayback Machine A comprehensive database of published data on equilibrium constants of metal complexes and ligands
  9. 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. S2CID 96848983.
  10. Siegel, Hardo; Eggersdorfer, Manfred (2002). "Ketones". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a15_077. ISBN 9783527306732.
  11. Denoon, C. E., Jr.; Adkins, Homer; Rainey, James L. (1940). "Acetylacetone". Organic Syntheses. 20: 6. doi:10.15227/orgsyn.020.0006.
  12. O'Brien, Brian. "Co(tfa)3 & Co(acac)3 handout" (PDF). Gustavus Adolphus College.
  13. 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". Biochemical Journal. 369 (3): 573–581. doi:10.1042/BJ20021047. PMC 1223103. PMID 12379146.
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.