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Acetylacetone
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Acetylacetone
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. Acetylacetone is a building block for the synthesis of many coordination complexes as well as heterocyclic compounds.
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. 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.
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. The enol form is a vinylogous analogue of a carboxylic acid.[citation needed]
Acetylacetone is a weak acid. It forms the acetylacetonate anion C5H7O−2 (commonly abbreviated 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 atom numbered C3 according to the IUPAC nomenclature of organic chemistry). These equivalencies are because there is a resonance between the four bonds in the O−C2−C3−C4−O linkage in the acetylacetonate anion. Each of the four bonds in the linkage has a bond order of about 1.5, and the two 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). 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.[citation needed]
Acetylacetone is prepared industrially by the thermal rearrangement of isopropenyl acetate.
Laboratory routes to acetylacetone also begin with acetone. Acetone and acetic anhydride ((CH3C(O))2O) upon the addition of boron trifluoride (BF3) catalyst:
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Acetylacetone
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. Acetylacetone is a building block for the synthesis of many coordination complexes as well as heterocyclic compounds.
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. 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.
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. The enol form is a vinylogous analogue of a carboxylic acid.[citation needed]
Acetylacetone is a weak acid. It forms the acetylacetonate anion C5H7O−2 (commonly abbreviated 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 atom numbered C3 according to the IUPAC nomenclature of organic chemistry). These equivalencies are because there is a resonance between the four bonds in the O−C2−C3−C4−O linkage in the acetylacetonate anion. Each of the four bonds in the linkage has a bond order of about 1.5, and the two 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). 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.[citation needed]
Acetylacetone is prepared industrially by the thermal rearrangement of isopropenyl acetate.
Laboratory routes to acetylacetone also begin with acetone. Acetone and acetic anhydride ((CH3C(O))2O) upon the addition of boron trifluoride (BF3) catalyst:
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