Acetoacetic acid is the
organic compoundAn organic compound is any member of a large class of chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of compounds such as carbonates, simple oxides of carbon and cyanides, as well as the allotropes of carbon, are considered inorganic...
with the formula CH
3C(O)CH
2CO
2H. It is the simplest beta-
keto acidKeto acids are organic acids containing a ketone functional group and a carboxylic acid group.Common types of keto acids include:*Alpha-keto acid, or 2-oxo acids, such as pyruvic acid have the keto group adjacent to the carboxylic acid...
group and like other members of this class is unstable.
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 acetoacetateThe organic compound ethyl acetoacetate is the ethyl ester of acetoacetic acid. It is a solvent, and is used as a chemical intermediate in the production of a wide variety of compounds, such as amino acids, analgesics, antibiotics, antimalarial agents, antipyrine and aminopyrine, and vitamin B1;...
followed by acidification of the anion.
In general, acetoacetic acid is generated at 0 °C and used in situ immediately.
Acetoacetic acid is the
organic compoundAn organic compound is any member of a large class of chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of compounds such as carbonates, simple oxides of carbon and cyanides, as well as the allotropes of carbon, are considered inorganic...
with the formula CH
3C(O)CH
2CO
2H. It is the simplest beta-
keto acidKeto acids are organic acids containing a ketone functional group and a carboxylic acid group.Common types of keto acids include:*Alpha-keto acid, or 2-oxo acids, such as pyruvic acid have the keto group adjacent to the carboxylic 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 acetoacetateThe organic compound ethyl acetoacetate is the ethyl ester of acetoacetic acid. It is a solvent, and is used as a chemical intermediate in the production of a wide variety of compounds, such as amino acids, analgesics, antibiotics, antimalarial agents, antipyrine and aminopyrine, and vitamin B1;...
followed by acidification of the anion.
In general, acetoacetic acid is generated at 0 °C and used in situ immediately. It decomposes at a moderate
rateThe reaction rate or rate of reaction for a reactant or product in a particular reaction is intuitively defined as how fast a reaction takes place...
to
acetoneAcetone is the organic compound with the formula OC2. This colorless, mobile, flammable liquid is the simplest example of the ketones. Owing to the fact that acetone is miscible with water it serves as an important solvent in its own right, typically as the solvent of choice for...
and
carbon dioxideCarbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state...
:
- CH3C(O)CH2CO2H → CH3C(O)CH3 + CO2
The acid form has a
half-lifeHalf-life is the period of time, for a substance undergoing decay, to decrease by half. The name originally was used to describe a characteristic of unstable atoms , but may apply to any quantity which follows a set-rate decay....
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.
Detection
When
ketone bodiesKetone bodies are three water-soluble compounds that are produced as by-products when fatty acids are broken down for energy in the liver and kidney. They are used as a source of energy in the heart and brain. In the brain, they are a vital source of energy during fasting...
are measured by way of urine concentration, acetoacetic acid, along with
beta-hydroxybutyric acidbeta-Hydroxybutyric acid is a ketone body. It is a chiral compound having two enantiomers,
D-3-hydroxybutyric acid and
L-3-hydroxybutyric acid. Like the other ketone bodies , levels of beta-hydroxybutyrate are raised in ketosis...
(BHB), and
acetoneAcetone is the organic compound with the formula OC2. This colorless, mobile, flammable liquid is the simplest example of the ketones. Owing to the fact that acetone is miscible with water it serves as an important solvent in its own right, typically as the solvent of choice for...
, 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 baseWithin the Brønsted-Lowry theory of acids and bases, a conjugate acid is the acid member, HX, of a pair of two compounds that transform into each other by gain or loss of a proton. A conjugate acid can also be seen as the chemical substance that releases, or donates, a proton in the forward...
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.