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Acetoacetate

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Acetoacetate

Acetoacetic acid
Identifiers
CAS number 541-50-4 YesY
PubChem 96
ChemSpider 94 YesY
DrugBank DB04025
KEGG C00164 YesY
ChEBI CHEBI:15344 YesY
Jmol-3D images Image 1
Properties
Molecular formula C4H6O3
Molar mass 102.088 g/mol
Appearance colorless, oily liquid
Melting point

36.5 °C, 310 K, 98 °F

Boiling point

Decomposes

Solubility in water miscible
Solubility soluble in ethanol, ether
Acidity (pKa) 3.58 [1]
 N (verify) (what is: YesY/N?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Acetoacetic acid (also called 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 is unstable. The methyl and ethyl esters, which are quite stable, are produced on a large scale industrially as precursors to dyes.[2]

Synthesis and properties

In general, the esters are prepared by 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 3.77.

Detection

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.

See also

References

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