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| Names | |
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| Preferred IUPAC name 3-Oxobutanoic acid[1] | |
| Systematic IUPAC name 3-Oxobutyric acid | |
| Other names Acetoacetic acid Diacetic acid Acetylacetic acid Acetonecarboxylic acid | |
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| 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 inethanol,ether |
| Acidity (pKa) | 3.58[2] |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Acetoacetic acid (IUPAC name:3-oxobutanoic acid, also known asacetonecarboxylic acid ordiacetic acid) is theorganic compound with the formula CH3COCH2COOH. It is the simplest beta-keto acid, and like other members of this class, it is unstable. Themethyl andethyl esters, which are quite stable, are produced on a large scale industrially as precursors to dyes. Acetoacetic acid is aweak acid.[3]
Under typical physiological conditions, acetoacetic acid exists as itsconjugate base,acetoacetate:
Unbound acetoacetate is primarily produced bylivermitochondria from itsthioester withcoenzyme A (CoA):
Theacetoacetyl-CoA itself is formed by three routes:
In mammals, acetoacetate produced in the liver (along with the other two "ketone bodies") is released into the bloodstream as an energy source during periods offasting, exercise, or as a result oftype 1 diabetes mellitus.[5] First, a CoA group is enzymatically transferred to it fromsuccinyl CoA, converting it back to acetoacetyl CoA; this is then broken into two acetyl CoA molecules by thiolase, and these then enter thecitric 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
Acetoacetic acid may be prepared by the hydrolysis ofdiketene. 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 moderatereaction rate intoacetone andcarbon dioxide:
The acid form has ahalf-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 preparetrifluoroacetone:
It is aweak acid (like most alkyl carboxylic acids), with apKa of 3.58.
Acetoacetic acid displays keto-enoltautomerisation, with the enol form being partially stabilised by extended conjugation and intramolecularH-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]
Acetoacetic esters are used for theacetoacetylation reaction, which is widely used in the production ofarylide yellows anddiarylide dyes.[3] Although the esters can be used in this reaction, diketene also reacts withalcohols andamines to the corresponding acetoacetic acid derivatives in a process calledacetoacetylation. An example is the reaction with 4-aminoindane:[10]
Acetoacetic acid is measured in the urine of people with diabetes to test forketoacidosis[11] and for monitoring people on aketogenic orlow-carbohydrate diet.[12][13] This is done using dipsticks coated innitroprusside or similar reagents. Nitroprusside changes from pink to purple in the presence of acetoacetate, theconjugate 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 ketoacidosisβ-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 indairy cows to test forketosis.[15]
