View source for Acetylacetone

 {{Chembox new|
 ImageFile=AcacH.png|
 IUPACName=Pentane-2,4-dione|
 Formula=C<sub>5</sub>H<sub>8</sub>O<sub>2</sub>|
 MolarMass=100.13 g/mol|
 CASNo=123-54-6|
 Density=0.98 g/ml|
 MeltingPt=&minus;23 °C|
 BoilingPt=140 °C|
 Solubility=16 g/100 mL|
 Solvent=Water|
 SMILES=CC(=O)CC(=O)C|
 Section1={{Chembox Hazards|
 EUClass=Harmful ('''Xn''')|
 EUIndex=606-029-00-0|
 NFPA-H=2|
 NFPA-F=2|
 NFPA-R=0|
 RPhrases={{R10}}, {{R22}}|
 SPhrases={{S2}}, {{S21}}, {{S23}}, {{S24/25}}|
 FlashPt=34 °C|
 Autoignition=340 °C|
 ExploLimits=2.4&ndash;11.6%}}}}


'''Acetylacetone''' is an [[organic compound]] with molecular formula C<sub>5</sub>H<sub>8</sub>O<sub>2</sub>. This [[diketone]] is formally named 2,4-pentanedione, although as discussed below, this name does not properly describe the predominant structure.  It is a precursor to common bidentate [[ligand]] and a building block for the synthesis of [[heterocyclic compound]]s. 

==Properties==
The keto and enol forms of acetylacetone coexist in solution; these forms are [[tautomers]]. The C<sub>2v</sub> [[molecular symmetry|symmetry]] for the enol form displayed on the right in ''scheme 1'' has been verified by many methods including [[microwave spectroscopy]].<ref>{{cite journal
| title = The C2v Structure of Enolic Acetylacetone
| author = W. Caminati, J.-U. Grabow
| journal =  [[Journal of the American Chemical Society]]
| year = 2006
| volume = 128
| issue =  3
| pages = 854 - 857
| doi = 10.1021/ja055333g
}}</ref> Hydrogen bonding in the enol reduces the steric repulsion between the cabonyl groups. In the gas phase K is 11.7. The equilibrium constant tends to be high in nonpolar solvents:
[[cyclohexane]] is 42, [[toluene]] is 10, [[Tetrahydrofuran|THF]] 7.2, [[dimethylsulfoxide]] (K=2), and water (K=0.23).<ref>''Solvents and Solvent Effects in Organic Chemistry'', Christian Reichardt Wiley-VCH; 3 edition 2003 ISBN 3-527-30618-8</ref>

[[Image:AcacH.png|300px|Scheme 1. Tautomerism of 2,4-pentanedione]]

==Preparation==
Two common procedures are used for synthesizing acetylacetone. [[Acetone]] and [[acetic anhydride]] react upon the addition of [[Boron trifluoride|BF<sub>3</sub>]] catalyst.
:(CH<sub>3</sub>CO)<sub>2</sub>O + CH<sub>3</sub>C(O)CH<sub>3</sub> → CH<sub>3</sub>C(O)CH<sub>2</sub>C(O)CH<sub>3</sub>
The second synthesis involves the base-catalyzed condensation of acetone and [[ethyl acetate]], followed by acidification
:NaOEt + EtO<sub>2</sub>CCH<sub>3</sub> + CH<sub>3</sub>C(O)CH<sub>3</sub> → NaCH<sub>3</sub>C(O)CHC(O)CH<sub>3</sub> + 2 EtOH
:NaCH<sub>3</sub>C(O)CHC(O)CH<sub>3</sub> + HCl → CH<sub>3</sub>C(O)CH<sub>2</sub>C(O)CH<sub>3</sub> + NaCl

Because of the ease of these syntheses, many analogues of acetylacetonates are known. Some examples include C<sub>6</sub>H<sub>5</sub>C(O)CH<sub>2</sub>C(O)C<sub>6</sub>H<sub>5</sub> (dbaH) and (CH<sub>3</sub>)<sub>3</sub>CC(O)CH<sub>2</sub>C(O)CC(CH<sub>3</sub>)<sub>3</sub>. Hexafluoroacetylacetonate is also widely used to generate volatile metal complexes.

==Acetylacetonate "anion"== 
C<sub>5</sub>H<sub>7</sub>O<sub>2</sub><sup>−</sup>, is the [[conjugate base]] of 2,4-pentanedione. In reality, the free ion does not exist in solution, but is bound to the corresponding cation, such as Na<sup>+</sup>. In practice, the existence of the free anion, commonly abbreviated '''acac<sup>−</sup>''', is a useful model.

==Coordination chemistry==
The acetylacetonate [[anion]] forms complexes with many [[transition metal]] ions wherein both oxygen atoms bind to the metal to form a six-membered chelate ring. Some examples include: Mn(acac)<sub>3</sub>,<ref name=snider>B. B. Snider, "Manganese(III) Acetylacetonate" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. {{doi|10.1002/047084289}}</ref> [[Vanadyl(acetylacetate)|VO(acac)<sub>2</sub>]], Fe(acac)<sub>3</sub>, and Co(acac)<sub>3</sub>. Any complex of the form M(acac)<sub>3</sub> is [[Chirality (chemistry)|chiral]] (has a non-superimposable mirror image). Additionally, M(acac)<sub>3</sub> complexes can be reduced electrochemically, with the reduction rate being dependent on the solvent and the metal center.<ref>{{cite journal
| title = Kinetic parameters for heterogeneous electron transfer to tris(acetylacetonato)manganese(III) and tris(acetylacetonato)iron(III) in aproptic solvents
| author = W. Fawcett, M. Opallo
| journal =  [[Journal of Electroanalytical Chemistry]]
| year = 1992
| volume = 331
| issue =  
| pages = 815-830
| doi = 10.1016/0022-0728(92)85008-Q
}}</ref> Bis- and tris complexes of the type M(acac)<sub>2</sub> and M(acac)<sub>3</sub> are typically soluble in organic solvents, in contrast to the related metal halides. Because of this properties, these complexes are widely used as [[catalyst]] precursors and reagents. Important applications include their use as NMR "shift reagents" and as catalysts for [[organic synthesis]], and precursors to industrial hydroformylation catalysts.

C<sub>5</sub>H<sub>7</sub>O<sub>2</sub><sup>&minus;</sup> in some cases also binds to metals through the central carbon atom; this bonding mode is more common for the third-row transition metals such as platinum(II) and iridium(III).

[[Image:ChiralityII.jpg|175px|Scheme 1. Chirality of M(acac)<sub>3</sub>]]

===Illustrative metal acetylacetonates===
====Chromium (III) acetylacetonate====

Cr(acac)<sub>3</sub> ([[CAS registry number]] 21679-31-2) is used as a spin relaxation agent to improve the sensitivity in quantitative [[Carbon-13 NMR]] spectroscopy.<ref>{{Citation
  | last =Caytan
  | first =Elsa
  | author-link =
  | last2 =Remaud, Gerald S.; Tenailleau, Eve; Akoka, Serge
  | first2 =
  | author2-link =
  | title =Precise and accurate quantitative <sup>13</sup>C NMR with reduced experimental time
  | journal =Talanta
  | volume =71
  | issue =3
  | pages =1016-1021
  | date =2007
  | year =
  | url =
  | doi =
  | id =  }}</ref>

====Copper(II) acetylacetonate====
Cu(acac)<sub>2</sub>, prepared by treating acetylacetone with aqueous Cu(NH<sub>3</sub>)<sub>4</sub><sup>2+</sup> and is available commercially, catalyzes coupling and carbene transfer reactions. 

[[Image:CuII.jpg|150px|Scheme 1. Structure of copper(II) acetylacetonate]]

====Copper(I) acetylacetonate====
Unlike the copper(II) chelate, copper(I) acetylacetonate is an air sensitive oligomeric species. It is employed to catalyze [[Michael addition]]s.<ref>E. J. Parish, S. Li "Copper(I) Acetylacetonate" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. {{doi|10.1002/047084289X.rc203}}</ref>

====Manganese(III) acetylacetonate====
[[Image:Lambda-tris(acetylacetonato)manganese(III)-3D-balls.png|thumb|right|200px|[[Ball-and-stick model]] of Λ-Mn(acac)<sub>3</sub>, with Jahn-Teller tetragonal elongation]]
Mn(acac)<sub>3</sub>, a one-electron oxidant, is used for coupling phenols.<ref name=snider/> It is prepared by the direct reaction of acetylacetone and [[potassium permanganate]]. In terms of electronic structure, Mn(acac)<sub>3</sub> is [[high spin]]. Its distorted octahedral structure reflects geometric distortions due to the [[Jahn-Teller effect]]. The two most common structures for this complex include one with tetrahedral elongation and one with tetragonal compression. For the elongation, two Mn-O bonds are 2.12 Å while the other four are 1.93 Å. For the compression, two Mn-O bonds are 1.95 and the other four are 2.00 Å. The effects of the tetrahedral elongation are noticeably more significant than the effects of the tetragonal compression.<ref>{{Cotton&Wilkinson6th}}</ref>

[[Image:Mnacac3.jpg|100px|Scheme 1. Structure of manganese(III) acetylacetonate]]

====Nickel(II) acetylacetonate====
"Nickel acac" is not Ni(acac)<sub>2</sub> but the trimer [Ni(acac)<sub>2</sub>]<sub>3</sub>. This emerald green solid, which is benzene soluble, is widely employed in the preparation of Ni(O) complexes. Upon exposure to the atmosphere, [Ni(acac)<sub>2</sub>]<sub>3</sub> converts to the chalky green monomeric hydrate.
===C-bonded acetylacetonates===
C<sub>5</sub>H<sub>7</sub>O<sub>2</sub><sup>−</sup> in some cases also binds to metals through the central carbon atom (C3); this bonding mode is more common for the third-row transition metals such as platinum(II) and iridium(III). The complexes Ir(acac)<sub>3</sub> and corresponding Lewis-base adducts Ir(acac)<sub>3</sub>L (L = an [[amine]]) contain one carbon-bonded acac ligand. The IR spectra of O-bonded acetylacetonates are characterized by relatively low-energy νCO bands of 1535 cm<sup>−1</sup>, whereas in carbon-bonded acetylacetonates, the carbonyl vibration occurs closer to the normal range for ketonic C=O, i.e. 1655 cm<sup>−1</sup>.

==Other reactions of acetylacetone==
*Deprotonations: Very strong bases will doubly deprotonate acetylacetone, starting at C3 but also at C1. The resulting species can then be alkylated at C-1.
*Precursor to heterocycles: Acetylacetone is a versatile precursor to heterocycles. Hydrazine reacts to produce pyrazoles. Urea gives pyrimidines.
*Precursor to related imino ligands: Acetylacetone condenses with amines to give, successively, the mono- and the di-[[diketimine]]s wherein the O atoms in acetylacetone are replaced by NR (R = aryl, alkyl).
*Enzymatic breakdown: The enzyme acetylacetone dioxygenase cleave the carbon-carbon bond of acetyacetone, producing acetate and 2-oxopropanal. The enzyme is Fe(II)-dependent, but it has been proven to bind to zinc as well. Acetylacetone degradation has been characterized in the bacterium ''Acinetobacter johnsonii''.<ref>Straganz, G.D., Glieder, A., Brecker, L., Ribbons, D.W. and Steiner, W. "Acetylacetone-Cleaving Enzyme Dke1: A Novel C-C-Bond-Cleaving Enzyme." Biochem. J. 369 (2003) 573-581 {{DOI|10.1042/BJ20021047}}</ref>
:C<sub>5</sub>H<sub>8</sub>O<sub>2</sub> + O<sub>2</sub> → C<sub>2</sub>H<sub>4</sub>O<sub>2</sub> + C<sub>3</sub>H<sub>4</sub>O<sub>2</sub>
*Arylation: Acetylacetonate displaced halides from certain halo-substituted benzoic acid. This reaction is copper-catalyzed.
:2-BrC<sub>6</sub>H<sub>4</sub>CO<sub>2</sub>H + NaC<sub>5</sub>H<sub>7</sub>O<sub>2</sub> → 2-(CH<sub>3</sub>CO)<sub>2</sub>HC)-C<sub>6</sub>H<sub>4</sub>CO<sub>2</sub>H + NaBr

== References==
<references/>

==Further reading==
*Bennett, M. A.; Heath, G. A.; Hockless, D. C. R.; Kovacik, I.; Willis, A. C. "Alkene Complexes of Divalent and Trivalent Ruthenium Stabilized by Chelation. Dependence of Coordinated Alkene Orientation on Metal Oxidation State" [[Journal of the American Chemical Society]] 1998: '''120''' (5) 932-941. {{doi|10.1021/ja973282k}}
*Albrecht, M. Schmid, S.; deGroot, M.; Weis, P.; Fröhlich, R. "Self-assembly of an Unpolar Enantiomerically Pure Helicate-type Metalla-cryptand" [[Chemical Communications]] 2003: 2526–2527. {{doi|10.1039/b309026d}}
*Charles, R. G., "Acetylacetonate manganese (III)" Inorganic Synthesis, 1963, '''7''', 183-184.
*Richert, S. A., Tsang, P. K. S., Sawyer, D. T., "Ligand-centered redox processes for manganese, iron and cobalt, MnL<sub>3</sub>, FeL<sub>3</sub>, and CoL<sub>3</sub>, complexes (L = acetylacetonate, 8-quinolinate, picolinate, 2,2'-bipyridyl, 1,10-phenanthroline) and for their tetrakis(2,6-dichlorophenyl)porphinato complexes[M(Por)]"[[Inorganic Chemistry]], 1989, '''28''', 2471-2475. {{doi|10.1021/ic00311a044}}
*Wong-Foy, A. G.; Bhalla, G.; Liu, X. Y.; Periana, R. A.. "Alkane C-H Activation and Catalysis by an O-Donor Ligated Iridium Complex." [[Journal of the American Chemical Society]], 2003: '''125''' (47) 14292-14293. {{doi|10.1021/ja037849a}}
*Tenn, W. J., III; Young, K. J. H.; Bhalla, G.; Oxgaard. J.; Goddard, W. A., III; Periana, R. A. "CH Activation with an O-Donor Iridium-Methoxo Complex." [[Journal of the American Chemical Society]], 2005: '''127''' (41) 14172-14173. {{doi|10.1021/ja051497l}}
* N. Barta, "Bis(acetylacetonato)zinc(II)" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. {{doi|10.1002/047084289X.rb097}}

== External links ==
*{{ICSC|0533|05}}

[[Category:Ketones]]
[[Category:chelating agents]]

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