|Preferred IUPAC name
Acetoacetic acid (no longer recommended)
3D model (Jmol)
|Molar mass||102.088 g/mol|
|Appearance||colorless, oily liquid|
|Melting point||36.5 °C (97.7 °F; 309.6 K)|
|Solubility||soluble in ethanol, ether|
|Acidity (pKa)||3.58 |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
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. Acetoacetic acid is a weak acid.
Acetoacetic acid is an intermediate in the metabolism of fatty acids in most organisms, specifically via the process of beta oxidation which converts it into Acetyl-CoA. In mammals it is also produced by the liver along with other ketone bodies and is released into the bloodstream as an energy source during periods of fasting, exercise, or as a result of type 1 diabetes mellitus. Under typical physiological conditions, acetoacetic acid exists as its conjugate base, acetoacetate.
Synthesis and properties
Acetoacetic acid may be prepared by the hydrolysis of diketene. Its esters are produced analogously via an reaction between diketene and alcohols, and acetoacetic acid can be prepared by the hydrolysis of these species. In general, acetoacetic acid is generated at 0 °C and used in situ immediately. 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. It is a weak acid (like most alkyl carboxylic acids), with a pKa of 3.58.
Acetoacetic acid displays keto-enol tautomerisation, with the enol form being partially stabilised by extended conjugation and intramolecular 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.
Acetoacetic esters are used for the acetoacetylation reaction, which is widely used in the production of arylide yellows and diarylide dyes. 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:
Acetoacetic acid is measured in the urine of people with diabetes to test for ketoacidosis and for monitoring people on a ketogenic or low-carbohydrate diet, 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 test does not measure β-hydroxybutyrate, the most abundant ketone in the body; during treatment of ketoacidosis β-hydroxybutyrate is converted to acetoacetate so the test is not useful after treatment begins and may be falsely low at diagnosis.
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