Acetylacetone

Last updated
Acetylacetone
Acetyloaceton.svg
Ball-and-stick model of the enol tautomer Acetylacetone-enol-tautomer-from-xtal-Mercury-3D-balls.png
Ball-and-stick model of the enol tautomer
Ball-and-stick model of the keto tautomer Acetylacetone-keto-tautomer-from-xtal-Mercury-3D-balls.png
Ball-and-stick model of the keto tautomer
Space-filling model of the enol tautomer Acetylacetone-enol-tautomer-from-xtal-Mercury-3D-sf.png
Space-filling model of the enol tautomer
Space-filling model of the keto tautomer Acetylacetone-keto-tautomer-from-xtal-Mercury-3D-sf.png
Space-filling model of the keto tautomer
Names
IUPAC names
(3Z)-4-Hydroxy-3-penten-2-one (enol form)
Pentane-2,4-dione (keto form)
Other names
  • Hacac
  • 2,4-Pentanedione
Identifiers
3D model (JSmol)
741937
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.004.214 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 204-634-0
2537
KEGG
PubChem CID
RTECS number
  • SA1925000
UNII
UN number 2310
  • InChI=1S/C5H8O2/c1-4(6)3-5(2)7/h3H2,1-2H3 Yes check.svgY
    Key: YRKCREAYFQTBPV-UHFFFAOYSA-N Yes check.svgY
  • 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
AppearanceColorless liquid
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:
GHS-pictogram-flamme.svg GHS-pictogram-skull.svg GHS-pictogram-exclam.svg GHS-pictogram-silhouette.svg
Danger
H226, H302, H311, H320, H331, H335, H341, H370, H412
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)
NFPA 704.svgHealth 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformFlammability 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 fuelInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
2
2
0
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).
Yes check.svgY  verify  (what is  Yes check.svgYX mark.svgN ?)

Acetylacetone is an organic compound with the chemical formula CH3−C(=O)−CH2−C(=O)−CH3. It is classified as a 1,3-diketone. It exists in equilibrium with a tautomer CH3−C(=O)−CH=C(−OH)−CH3. The mixture is a colorless liquid. These tautomers interconvert so rapidly under most conditions that they are treated as a single compound in most applications. [2] Acetylacetone is a building block for the synthesis of many coordination complexes as well as heterocyclic compounds.

Contents

Properties

Tautomerism

SolventKketo→enol
Gas phase 11.7
Cyclohexane 42
Toluene 10
THF 7.2
CDCl3 [3] 5.7
DMSO 2
Water 0.23
Acetylaceton-Tautomerie.svg

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 Kketo→enol is equal or greater than 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.[ citation needed ]

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. It forms the acetylacetonate anion C5H7O2 (commonly abbreviated acac):

C5H8O2 ⇌ C5H7O2 + H+
The structure of the acetylacetonate anion (
acac) Acetylacetonate anion.png
The structure of the acetylacetonate anion (acac)

In the acetylacetonate anion, both C-O bonds are equivalent. Both C-C central bonds are equivalent as well, with one hydrogen atom bonded to the central carbon atom (the C3 atom). Those two equivalencies are because there is a resonance between the four bonds in the O-C2-C3-C4-O linkage in the acetylacetonate anion, where the bond order of those four bonds is about 1.5. Both oxygen atoms equally share the negative charge. The acetylacetonate anion is a bidentate ligand.

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 the carbon atom at the position 1.

Preparation

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

Acetylacetone synthesis01.svg

Laboratory routes to acetylacetone also begin with acetone. Acetone and acetic anhydride ((CH3C(O))2O) upon the addition of boron trifluoride (BF3) catalyst: [11]

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

A second synthesis involves the base-catalyzed condensation (e.g., by sodium ethoxide CH3CH2ONa+) of acetone and ethyl acetate, followed by acidification of the sodium acetylacetonate (e.g., by hydrogen chloride HCl): [11]

CH3CH2ONa+ + CH3C(O)OCH2CH3 + CH3C(O)CH3 → Na+[CH3C(O)CHC(O)CH3] + 2 CH3CH2OH
Na+[CH3C(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 are benzoylacetone, dibenzoylmethane (dbaH)[ clarification needed ] and tert-butyl analogue 2,2,6,6-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 may undergo condensation. For example, condensation with Hydrazine produces pyrazoles while condensation with Urea provides pyrimidines. Condensation with two aryl- or alkylamines 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 Vanadyl-acetylacetonate-from-xtal-3D-balls.png
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 + O2C2H4O2 + C3H4O2

Related Research Articles

<span class="mw-page-title-main">Carboxylic acid</span> Organic compound containing a –C(=O)OH group

In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group attached to an R-group. The general formula of a carboxylic acid is often written as R−COOH or R−CO2H, sometimes as R−C(O)OH with R referring to an organyl group, or hydrogen, or other groups. Carboxylic acids occur widely. Important examples include the amino acids and fatty acids. Deprotonation of a carboxylic acid gives a carboxylate anion.

<span class="mw-page-title-main">Ether</span> Organic compounds made of alkyl/aryl groups bound to oxygen (R–O–R)

In organic chemistry, ethers are a class of compounds that contain an ether group—an oxygen atom bonded to two organyl groups. They have the general formula R−O−R′, where R and R′ represent the organyl groups. Ethers can again be classified into two varieties: if the organyl groups are the same on both sides of the oxygen atom, then it is a simple or symmetrical ether, whereas if they are different, the ethers are called mixed or unsymmetrical ethers. A typical example of the first group is the solvent and anaesthetic diethyl ether, commonly referred to simply as "ether". Ethers are common in organic chemistry and even more prevalent in biochemistry, as they are common linkages in carbohydrates and lignin.

<span class="mw-page-title-main">Ketone</span> Organic compounds of the form >C=O

In organic chemistry, a ketone is an organic compound with the structure R−C(=O)−R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group −C(=O)−. The simplest ketone is acetone, with the formula (CH3)2CO. Many ketones are of great importance in biology and in industry. Examples include many sugars (ketoses), many steroids, and the solvent acetone.

<span class="mw-page-title-main">Aldehyde</span> Organic compound containing the functional group R−CH=O

In organic chemistry, an aldehyde is an organic compound containing a functional group with the structure R−CH=O. The functional group itself can be referred to as an aldehyde but can also be classified as a formyl group. Aldehydes are a common motif in many chemicals important in technology and biology.

In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are Lewis bases.

<span class="mw-page-title-main">Acetoacetic acid</span> Chemical compound

Acetoacetic acid is the organic compound with the formula CH3COCH2COOH. It is the simplest beta-keto acid, and like other members of this class, it is unstable. The methyl and ethyl esters, which are quite stable, are produced on a large scale industrially as precursors to dyes. Acetoacetic acid is a weak acid.

<span class="mw-page-title-main">Dicarbonyl</span> Molecule containing two adjacent C=O groups

In organic chemistry, a dicarbonyl is a molecule containing two carbonyl groups. Although this term could refer to any organic compound containing two carbonyl groups, it is used more specifically to describe molecules in which both carbonyls are in close enough proximity that their reactivity is changed, such as 1,2-, 1,3-, and 1,4-dicarbonyls. Their properties often differ from those of monocarbonyls, and so they are usually considered functional groups of their own. These compounds can have symmetrical or unsymmetrical substituents on each carbonyl, and may also be functionally symmetrical or unsymmetrical.

<span class="mw-page-title-main">Enol</span> Organic compound with a C=C–OH group

In organic chemistry, alkenols are a type of reactive structure or intermediate in organic chemistry that is represented as an alkene (olefin) with a hydroxyl group attached to one end of the alkene double bond. The terms enol and alkenol are portmanteaus deriving from "-ene"/"alkene" and the "-ol" suffix indicating the hydroxyl group of alcohols, dropping the terminal "-e" of the first term. Generation of enols often involves deprotonation at the α position to the carbonyl group—i.e., removal of the hydrogen atom there as a proton H+. When this proton is not returned at the end of the stepwise process, the result is an anion termed an enolate. The enolate structures shown are schematic; a more modern representation considers the molecular orbitals that are formed and occupied by electrons in the enolate. Similarly, generation of the enol often is accompanied by "trapping" or masking of the hydroxy group as an ether, such as a silyl enol ether.

<span class="mw-page-title-main">Tautomer</span> Structural isomers of chemical compounds that readily interconvert

Tautomers are structural isomers of chemical compounds that readily interconvert. The chemical reaction interconverting the two is called tautomerization. This conversion commonly results from the relocation of a hydrogen atom within the compound. The phenomenon of tautomerization is called tautomerism, also called desmotropism. Tautomerism is for example relevant to the behavior of amino acids and nucleic acids, two of the fundamental building blocks of life.

<span class="mw-page-title-main">Acetone</span> Organic compound ((CH3)2CO); simplest ketone

Acetone is an organic compound with the formula (CH3)2CO. It is the simplest and smallest ketone. It is a colorless, highly volatile and flammable liquid with a characteristic pungent odor.

<span class="mw-page-title-main">Meldrum's acid</span> Chemical compound

Meldrum's acid or 2,2-dimethyl-1,3-dioxane-4,6-dione is an organic compound with formula C6H8O4. Its molecule has a heterocyclic core with four carbon and two oxygen atoms; the formula can also be written as [−O−(C 2)−O−(C=O)−(CH2)−(C=O)−].

<span class="mw-page-title-main">Ethyl acetoacetate</span> Chemical compound

The organic compound ethyl acetoacetate (EAA) is the ethyl ester of acetoacetic acid. It is a colorless liquid. It is widely used as a chemical intermediate in the production of a wide variety of compounds. It is used as a flavoring for food.

<span class="mw-page-title-main">Nickel(II) bis(acetylacetonate)</span> Coordination complex

Nickel(II) bis(acetylacetonate) is a coordination complex with the formula [Ni(acac)2]3, where acac is the anion C5H7O2 derived from deprotonation of acetylacetone. It is a dark green paramagnetic solid that is soluble in organic solvents such as toluene. It reacts with water to give the blue-green diaquo complex Ni(acac)2(H2O)2.

<span class="mw-page-title-main">Ruthenium(III) acetylacetonate</span> Chemical compound

Ruthenium(III) acetylacetonate is a coordination complex with the formula Ru(O2C5H7)3. O2C5H7 is the ligand called acetylacetonate. This compound exists as a dark violet solid that is soluble in most organic solvents. It is used as a precursor to other compounds of ruthenium.

Metal acetylacetonates are coordination complexes derived from the acetylacetonate anion (CH
3
COCHCOCH
3
) and metal ions, usually transition metals. The bidentate ligand acetylacetonate is often abbreviated acac. Typically both oxygen atoms bind to the metal to form a six-membered chelate ring. The simplest complexes have the formula M(acac)3 and M(acac)2. Mixed-ligand complexes, e.g. VO(acac)2, are also numerous. Variations of acetylacetonate have also been developed with myriad substituents in place of methyl (RCOCHCOR). Many such complexes are soluble in organic solvents, in contrast to the related metal halides. Because of these properties, acac complexes are sometimes used as catalyst precursors and reagents. Applications include their use as NMR "shift reagents" and as catalysts for organic synthesis, and precursors to industrial hydroformylation catalysts. C
5
H
7
O
2
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).

<span class="mw-page-title-main">Vanadyl acetylacetonate</span> Chemical compound

Vanadyl acetylacetonate is the chemical compound with the formula VO(acac)2, where acac is the conjugate base of acetylacetone. It is a blue-green solid that dissolves in polar organic solvents. The coordination complex consists of the vanadyl group, VO2+, bound to two acac ligands via the two oxygen atoms on each. Like other charge-neutral acetylacetonate complexes, it is not soluble in water.

<span class="mw-page-title-main">Dibenzoylmethane</span> Chemical compound

Dibenzoylmethane (DBM) is an organic compound with the formula (C6H5C(O))2CH2. DBM is the name for a 1,3-diketone, but the compound exists primarily as one of two equivalent enol tautomers. DBM is a white solid. Due UV-absorbing properties, derivatives of DBM such as avobenzone, have found applications as sunscreen products.

<span class="mw-page-title-main">1,1,1-Trifluoroacetylacetone</span> Chemical compound

1,1,1-Trifluoroacetylacetone is the organofluorine compound with the formula CF3C(O)CH2C(O)CH3. It is a colorless liquid. Like other 1,3-diketones, it is used as a precursor to heterocycles, e.g. pyrazoles, and metal chelates. It is prepared by condensation of esters of trifluoroacetic acid with acetone.

<span class="mw-page-title-main">Tetraacetylethane</span> Chemical compound

Tetraacetylethane is the organic compound with the nominal formula [CH(C(O)CH3)2]2. It is a white solid that has attracted interest as a precursor to heterocycles and metal complexes. It is prepared by oxidation of sodium acetylacetonate:

<span class="mw-page-title-main">Sodium acetylacetonate</span> Chemical compound

Sodium acetylacetonate is an organic compound with the nominal formula Na[CH(C(O)CH3)2]. This white, water-soluble solid is the conjugate base of acetylacetone.

References

  1. "05581: Acetylacetone". Sigma-Aldrich.
  2. Thomas M. Harris (2001). "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. 1 2 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.