Acetoacetic acid

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Acetoacetic acid
Acetoacetic acid.png
Acetoacetic-acid-3D-balls.png
Names
IUPAC name
3-oxobutanoic acid, diacetic acid
Identifiers
541-50-4 YesY
ChEBI CHEBI:15344 YesY
ChEMBL ChEMBL1230762 N
ChemSpider 94 YesY
DrugBank DB01762 N
Jmol 3D model Interactive image
KEGG C00164 YesY
PubChem 96
Properties
C4H6O3
Molar mass 102.088 g/mol
Appearance colorless, oily liquid
Melting point 36.5 °C (97.7 °F; 309.6 K)
Boiling point Decomposes
soluble
Solubility soluble in ethanol, ether
Acidity (pKa) 3.58 [1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YesYN ?)
Infobox references

Acetoacetic acid (also diacetic acid) is the organic compound with the formula CH3COCH2COOH. It is the simplest beta-keto acid group, 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.[2]

Acetoacetic acid is a weak acid. It is of biochemical importance in various animals, including humans, as one of the endogenous ketone bodies produced by the liver when it breaks down fatty acids into Acetyl-CoA and TCA cycle intermediates are depleted (particularly oxaloacetate, which is formed from pyruvate derived from glycolysis). It can be viewed as the product of joining two acetic acid molecules via a condensation reaction that ejects a water molecule in the process, although that is only one of the ways of forming the acetoacetate molecule. In the human body, a large portion of acetoacetate is converted to beta-hydroxybutyrate, a rich energy source for the brain, which cannot run directly on fatty acids themselves due to their poor ability to cross the blood-brain barrier.

Synthesis and properties[edit]

In general, the esters are prepared from diketene by treatment with alcohols.[2] Acetoacetic acid can be prepared by the hydrolysis of the ethyl acetoacetate followed by acidification of the anion.[3] In general, acetoacetic acid is generated at 0 °C and used in situ immediately.[4] It decomposes at a moderate rate to 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.[5]

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

Applications[edit]

Acetoacetic esters are used for the acetoacetylation reaction, which is widely used in the production of arylide yellows and diarylide dyes.[2] 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 2-aminoindane:[6]

Diketene reaction Sai 2007
Pigment Yellow 16 is a typical dye containing the acetoacetyl group

Detection[edit]

When ketone bodies are measured by way of urine concentration, acetoacetic acid, along with beta-hydroxybutyric acid (BHB), and acetone, is what is detected. This is done using dipsticks coated in nitroprusside or similar reagents. Nitroprusside changes from pink to purple in the presence of acetoacetate, the conjugate base of acetoacetic acid, and the colour change is graded by eye. The popular dipstick used to detect ketone bodies in urine "Ketostix" by Bayer, only detects acetoacetate, not BHB or acetone.[citation needed]

See also[edit]

References[edit]

  1. ^ Dawson, R. M. C., et al., Data for Biochemical Research, Oxford, Clarendon Press, 1959.
  2. ^ a b c Franz Dietrich Klingler, Wolfgang Ebertz "Oxocarboxylic Acids" in Ullmann's Encyclopedia of Industrial Chemistry 2005, Wiley-VCH, Weinheim. doi:10.1002/14356007.a18 313
  3. ^ Robert C. Krueger (1952). "Crystalline Acetoacetic Acid". Journal of the American Chemical Society 74 (21): 5536–5536. doi:10.1021/ja01141a521. 
  4. ^ George A. Reynolds and J. A. VanAllan "Methylglyoxal-ω-Phenylhydrazone" Organic Syntheses, Collected Volume 4, p.633 (1963).http://www.orgsyn.org/orgsyn/pdfs/CV4P0633.pdf
  5. ^ Hay, R. W.; Bond, M. A. (1967). "Kinetics of decarboxilation of acetoacetic acid". Aust. J. Chem. 20 (9): 1823–8. doi:10.1071/CH9671823. 
  6. ^ Kiran Kumar Solingapuram Sai; Thomas M. Gilbert; Douglas A. Klumpp (2007). "Knorr Cyclizations and Distonic Superelectrophiles". J. Org. Chem. 72 (25): 9761–9764. doi:10.1021/jo7013092. PMID 17999519.