Acetoacetic acid

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Acetoacetic acid
Names
Preferred IUPAC name
3-Oxobutanoic acid[1]
Systematic IUPAC name
3-Oxobutyric acid
Other names
Acetoacetic acid
Diacetic acid
Acetylacetic acid
Acetonecarboxylic acid
Identifiers
3D model (
JSmol
)
ChEBI
ChEMBL
ChemSpider
DrugBank
KEGG
UNII
  • InChI=1S/C4H6O3/c1-3(5)2-4(6)7/h2H2,1H3,(H,6,7) checkY
    Key: WDJHALXBUFZDSR-UHFFFAOYSA-N checkY
  • InChI=1/C4H6O3/c1-3(5)2-4(6)7/h2H2,1H3,(H,6,7)
    Key: WDJHALXBUFZDSR-UHFFFAOYAH
  • O=C(C)CC(=O)O
Properties
C4H6O3
Molar mass 102.089 g·mol−1
Appearance Colorless, oily liquid
Melting point 36.5 °C (97.7 °F; 309.6 K)
Boiling point Decomposes
Soluble
Solubility in organic solvents Soluble in ethanol, ether
Acidity (pKa) 3.58[2]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)

Acetoacetic acid (

weak acid.[3]

Biochemistry

Under typical physiological conditions, acetoacetic acid exists as its

conjugate base
, acetoacetate:

Ac
CH2CO2H → AcCH2CO−2 + H+

Unbound acetoacetate is primarily produced by

mitochondria from its thioester with coenzyme A
(CoA):

AcCH2C(O)−CoA + OH− → AcCH2CO−2 + H−CoA

The acetoacetate-CoA itself is formed by three routes:

  • 3-hydroxy-3-methylglutaryl CoA releases acetyl CoA and acetoacetate:
    −O2CCH2−C(
    Me
    )(OH)−CH2C(O)−CoA → −O2CCH2−Ac + Ac−CoA
  • Acetoacetyl-CoA can come from beta oxidation of butyryl-CoA:
    Et−CH2C(O)−CoA + 2NAD+ + H2O + FAD → Ac−CH2C(O)−CoA + 2NADH + FADH2
  • Condensation of pair of acetyl CoA molecules as catalyzed by thiolase.[4]: 393 
    2Ac−CoA → AcCH2C(O)−CoA + H−CoA

In mammals, acetoacetate produced in the liver (along with the other two "

succinyl CoA, converting it back to acetoacetyl CoA; this is then broken into two acetyl CoA molecules by thiolase, and these then enter the citric acid cycle. Heart muscle and renal cortex prefer acetoacetate over glucose. The brain uses acetoacetate when glucose levels are low due to fasting or diabetes.[4]
: 394 

Synthesis and properties

Acetoacetic acid may be prepared by the hydrolysis of diketene. Its esters are produced analogously via reactions between diketene and alcohols,[3] and acetoacetic acid can be prepared by the hydrolysis of these species.[6] In general, acetoacetic acid is generated at 0 °C and used in situ immediately.[7]

It decomposes at a moderate reaction rate into acetone and carbon dioxide:

CH3C(O)CH2CO2H → CH3C(O)CH3 + CO2

The acid form has a half-life of 140 minutes at 37 °C in water, whereas the basic form (the anion) has a half-life of 130 hours. That is, it reacts about 55 times more slowly.[8] The corresponding decarboxylation of trifluoroacetoacetate is used to prepare trifluoroacetone:

CF3C(O)CH2CO2H → CF3C(O)CH3 + CO2

It is a

weak acid (like most alkyl carboxylic acids), with a pKa
of 3.58.

Acetoacetic acid displays keto-enol

H-bonding. The equilibrium is strongly solvent depended; with the keto form dominating in polar solvents (98% in water) and the enol form accounting for 25-49% of material in non-polar solvents.[9]

Applications

Pigment Yellow 16 is a typical dye containing the acetoacetyl group

Acetoacetic esters are used for the

diarylide dyes.[3] Although the esters can be used in this reaction, diketene also reacts with alcohols and amines to the corresponding acetoacetic acid derivatives in a process called acetoacetylation. An example is the reaction with 4-aminoindane:[10]

Diketene reaction Sai 2007

Detection

Acetoacetic acid is measured in the urine of people with diabetes to test for

β-hydroxybutyrate is converted to acetoacetate so the test is not useful after treatment begins[11] and may be falsely low at diagnosis.[14]

Similar tests are used in

dairy cows to test for ketosis.[15]

See also

References

  1. ISBN 978-0-85404-182-4
    .
  2. ^ Dawson, R. M. C., et al., Data for Biochemical Research, Oxford, Clarendon Press, 1959.
  3. ^
    ISBN 978-3527306732
    .
  4. ^
    Biochemistry
    (2nd ed.).
  5. ISBN 0-7167-2009-4
    .
  6. doi:10.1021/ja01141a521
    .
  7. doi:10.15227/orgsyn.032.0084
    ; Collected Volumes, vol. 4, p. 633.
  8. doi:10.1071/CH9671823
    .
  9. ISSN 0022-3263
    .
  10. PMID 17999519
    .
  11. ^
    PMID 26975543
    .
  12. S2CID 21195842
    .
  13. PMID 24351673
    .
  14. S2CID 2819002
    .
  15. PMID 27435643
    .
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