acetoacetic acid

Acetoacetic acid
IUPAC name	3-oxobutanoic acid, diacetic acid
Identifiers
CAS number	541-50-4 Y
PubChem	96
SMILES	O=C(C)CC(=O)O
InChI	1/C4H6O3/c1-3(5)2-4(6)7/h2H2,1H3,(H,6,7)
InChI key	WDJHALXBUFZDSR-UHFFFAOYAH
ChemSpider ID	94
Properties
Molecular formula	C4H6O3
Molar mass	102.09 g/mol
Melting point	36.5 °C
Boiling point	Decomposes
Acidity (pKa)	3.77
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Acetoacetic acid is the organic compound with the formula CH₃C(O)CH₂CO₂H. It is the simplest beta-keto acid group and like other members of this class is unstable.

Synthesis and properties

Acetoacetic acid is a weak acid (like most alkyl carboxylic acids) with a pK_a of 3.77. It can be prepared by the hydrolysis of the ethyl acetoacetate followed by acidification of the anion.^[1] In general, acetoacetic acid is generated at 0 °C and used in situ immediately.^[2] 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 50 times more slowly.^[3]

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

• 3-hydroxybutyrate dehydrogenase

References