“Acetylacetone”的意思、由来-开放百科全书

Acetylacetone is an organic compound with the formula CH₃COCH₂COCH₃. It is a colorless liquid, classified as a 1,3-diketone. It exists in equilibrium with a tautomer CH₃C(O)CH=C(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.

Properties

Tautomerism

The keto and enol tautomers of acetylacetone coexist in solution. The enol form has C_2v symmetry, meaning the hydrogen atom is shared equally between the two oxygen atoms.^[3] In the gas phase, the equilibrium constant, K_keto→enol, is 11.7, favoring the enol form. The two tautomeric forms can be distinguished by NMR spectroscopy, IR spectroscopy and other methods.^[4]^[5]

The equilibrium constant tends to be high in nonpolar solvents; the keto form becomes more favorable in polar, hydrogen-bonding solvents, such as water.^[6] The enol form is a vinylogous analogue of a carboxylic acid.{{clear|left}}

Acid–base properties

IUPAC recommended pK_a 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).^[8] Values for mixed solvents are available. Very strong bases, such as organolithium compounds, will deprotonate acetylacetone twice. The resulting dilithio species can then be alkylated at C-1.{{clear|left}}

Preparation

Acetylacetone is prepared industrially by the thermal rearrangement of isopropenyl acetate.^[9]

Laboratory routes to acetylacetone begin also with acetone. Acetone and acetic anhydride upon the addition of boron trifluoride (BF₃) catalyst:^[10]

A second synthesis involves the base-catalyzed condensation of acetone and ethyl acetate, followed by acidification:^[10]

Because of the ease of these syntheses, many analogues of acetylacetonates are known. Some examples include C₆H₅C(O)CH₂C(O)C₆H₅ (dbaH) and (CH₃)₃CC(O)CH₂C(O)CC(CH₃)₃. Hexafluoroacetylacetonate is also widely 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

The acetylacetonate anion, acac⁻, forms complexes with many transition metal ions. A general method of synthesis is to treat a metal salt with acetylacetone in the presence of a base:^[11]

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

Enzymatic breakdown: 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.^[12]

References

1. ^{{cite web|url=http://www.sigmaaldrich.com/catalog/product/sial/05581?lang=en®ion=GB|website=Sigma-Aldrich|title=05581: Acetylacetone}}
2. ^{{cite encyclopedia|title=2,4‐Pentanedione|encyclopedia= e-EROS Encyclopedia of Reagents for Organic Synthesis|author=Thomas M. Harris|doi=10.1002/047084289X.rp030|year=2001|}}
3. ^{{cite journal|title=The C_2v Structure of Enolic Acetylacetone|first1=W.|last1=Caminati|first2=J.-U.|last2=Grabow|year=2006|journal=J. Am. Chem. Soc.|volume=128|issue=3|pages=854–857|doi=10.1021/ja055333g|pmid=16417375}}
4. ^{{cite journal|title=Substituent Effects on Keto–Enol Equilibria Using NMR Spectroscopy|first1=Kimberly A.|last1=Manbeck|first2=Nicholas C.|last2=Boaz|first3=Nathaniel C.|last3=Bair|first4=Allix M. S.|last4=Sanders|first5=Anderson L.|last5=Marsh|year=2011|journal=J. Chem. Educ.|volume=88|issue=10|pages=1444–1445|doi=10.1021/ed1010932}}
5. ^{{cite journal|title=Intramolecular hydrogen bond in enol form of 3-substituted-2,4-pentanedione|journal=Tetrahedron|year=1970|volume=26|pages=5691–5697|doi=10.1016/0040-4020(70)80005-9|first1=Z.|last1=Yoshida|first2=H.|last2=Ogoshi|first3=T.|last3=Tokumitsu}}
6. ^{{cite book|title=Solvents and Solvent Effects in Organic Chemistry|first=Christian|last=Reichardt|publisher=Wiley-VCH|edition= 3rd|date= 2003|ISBN=3-527-30618-8}}
7. ^IUPAC SC-Database A comprehensive database of published data on equilibrium constants of metal complexes and ligands
8. ^{{cite journal|last=Stary|first=J.|last2=Liljenzin|first2= J. O.|year=1982|title=Critical evaluation of equilibrium constants involving acetylacetone and its metal chelates|volume=54|issue=12|pages=2557–2592| doi=10.1351/pac198254122557| url=http://www.iupac.org/publications/pac/pdf/1982/pdf/5412x2557.pdf|journal=Pure and Applied Chemistry}}
9. ^{{cite encyclopedia|encyclopedia=Ullmann's Encyclopedia of Industrial Chemistry|location=Weinheim |publisher=Wiley-VCH |first=Hardo|last=Siegel|first2=Manfred|last2=Eggersdorfer|title=Ketones|doi=10.1002/14356007.a15_077|date=2002}}
10. ^¹{{OrgSynth | title = Acetylacetone | author = C. E. Denoon, Jr. | collvol = 3 | collvolpages = 16 | prep = cv3p0016}}
11. ^{{cite web|url=http://homepages.gac.edu/~bobrien/Inorganic_Lab/acac/Co.tfa.3.&.Co.acac.3.handout.S01.pdf|title=Co(tfa)₃ & Co(acac)₃ handout|first=Brian|last= O'Brien|publisher= Gustavus Adolphus College}}
12. ^{{cite journal|last1=Straganz|first1=G.D.|last2=Glieder|first2=A.|last3=Brecker|first3=L.|last4=Ribbons|first4=D.W.|last5=Steiner|first5=W.|year=2003|title=Acetylacetone-cleaving enzyme Dke1: a novel C–C-bond-cleaving enzyme from Acinetobacter johnsonii|url=|journal=Biochem. J.|pmid=12379146|volume=369|issue=3|pmc=1223103|pages=573–581|doi=10.1042/BJ20021047}}