Acetylacetone
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2008-06-22T21:54:30Z
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:'''''Acac''' redirects here. For other uses, see [[ACAC]].''
{{Chembox new|
ImageFile=AcacH.png|
IUPACName=Pentane-2,4-dione|
OtherNames=Hacac|
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=−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=2.4–11.6%}}}}
'''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. It is a precursor to acetylacetonate (abbreviated '''acac'''), a common bidentate [[ligand]]. It is also 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 left 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 carbonyl 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, [[dimethyl sulfoxide]] (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> The enol form is a [[vinylogous]] analogue of a [[carboxylic acid]].
[[Image:AcacH.png|300px|Scheme 1. Tautomerism of 2,4-pentanedione]]
==Preparation==
Acetylacetone is prepared industrially by the thermal rearrangement of isopropenylacetate.<ref>Hardo Siegel, Manfred Eggersdorfer “Ketones” in Ullmann’s Encyclopedia of Industrial Chemistry, Wiley-VCH, 2002, Wienheim. {{DOI|10.1002/14356007.a15_077}}</ref>
:Me<sub>2</sub>CHOC(O)Me → MeC(O)CH<sub>2</sub>C(O)Me
Laboratory routes to acetylacetone begin also with [[acetone]]. Acetone and [[acetic anhydride]] upon the addition of [[Boron trifluoride|BF<sub>3</sub>]] catalyst:<ref name = denoon>{{OrgSynth | title = Acetylacetone | author = C. E. Denoon, Jr. | collvol = 3 | collvolpages = 16 | prep = cv3p016}}</ref>
:(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>
A second synthesis involves the base-catalyzed condensation of acetone and [[ethyl acetate]], followed by acidification:<ref name = denoon/>
: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==
The acetylacetonate anion, C<sub>5</sub>H<sub>7</sub>O<sub>2</sub><sup>−</sup>, is the [[conjugate base]] of 2,4-pentanedione. It does not exist as a free ion 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.
Sodium acetylacetonate may be prepared by deprotonating acetylacetone with [[sodium hydroxide]] in a mixture of water-[[methanol]].<ref>{{OrgSynth | collvol = 4 | collvolpages = 869 | year = 1963 | prep = cv4p0869 | title = Tetraacetylethane | author = Robert G. Charles}}</ref>
==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 these 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>−</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>]]
===Metal acetylacetonates===
====Chromium(III) acetylacetonate====
[[Chromium(III) acetylacetonate|Cr(acac)<sub>3</sub>]] 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:Cu(II) acac.png|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:Mn(III) acac.png|150px|Scheme 1. Structure of manganese(III) acetylacetonate]]
====Nickel(II) acetylacetonate====
[[Image:Bis(acetylacetonato)nickel(II)-3D-sticks.png|thumb|right|200px|Stick model of [Ni(acac)<sub>2</sub>]<sub>3</sub>]]
"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.
====Vanadyl acetylacetonate====
[[Image:Vanadyl-acetoacetonate-3D-balls.png|thumb|right|200px|A [[ball-and-stick model]] of VO(acac)<sub>2</sub>]]
[[Vanadyl acetylacetonate]] is a blue complex with the formula V(O)(acac)<sub>2</sub>. It is useful in epoxidation of allylic alcohols.
<br clear = right/>
====Zinc acetylacetonate====
The monoaquo complex Zn(acac)<sub>2</sub>H<sub>2</sub>O (m.p. 138-140 °C) is pentacoordinate, adopting a square pyramidal structure.<ref>H. Montgomery and E. C. Lingafelter "The crystal structure of monoaquobisacetylacetonatozinc" Acta Crystallographica (1963), volume 16, pp. 748-752. doi:10.1107/S0365110X6300195X.</ref> Dehydration of this species gives the hygroscopic anhydrous derivative (m.p. 127 °C). <ref>G. Rudolph and M. C. Henry "Bis(2,4-Pentanedionato)zinc (Zinc Acetylacetonate)" Inorganic Syntheses, 1967, volume X, pp. 74-77.</ref> This more volatile derivative has been used as a precursor to films of [[zinc oxide|ZnO]].
====Iridium acetylacetonates====
Both iridium(I) and Ir(III) form stable acetylacetonato complexes. The Ir(III) derivatives include ''trans''-Ir(acac)<sub>2</sub>(''C''H(COMe)<sub>2</sub>)(H<sub>2</sub>O) and the more conventional ''D''<sub>3</sub>-symmetric Ir(acac)<sub>3</sub>. The C-bonded derivative is a precursor to homogeneous catalysts for [[C-H activation]] and related chemistries.<ref>Bennett, M. A.; Mitchell, T. R. B. "γ-Carbon-bonded 2,4-pentanedionato complexes of trivalent iridium" Inorganic Chemistry 1976, volume 15, pp. 2936-8. {{DOI|10.1021/ic50165a079}}</ref><ref>Bhalla, G.; Oxgaard, J.; Goddard, W. A., II, and Periana, R. A., "Hydrovinylation of Olefins Catalyzed by an Iridium Complex via CH Activation", Organometallics, 2005, 24, 5499-5502.{{doi|10.1021/om050614i}}</ref> Iridium(I) derivatives include square-planar Ir(acac)(CO)<sub>2</sub> (''C''<sub>2v</sub>-symmetry).
====Aluminium(III) acetylacetonate====
Al(C<sub>5</sub>H<sub>7</sub>O<sub>2</sub>)<sub>n</sub>, or shortened to Al(acac)
<br><br><br>
===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]] cleaves 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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[[fr:Acétylacétone]]
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[[ja:アセチルアセトン]]
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[[zh:乙酰丙酮]]