Acetoacetic acid
Encyclopedia
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.
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 rate
to acetone
and carbon dioxide
:
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.
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.
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...
with the formula CH3C(O)CH2CO2H. It is the simplest beta-keto acid
Keto acid
Keto acids are organic compounds that contain a carboxylic acid group and a ketone group. The alpha-keto acids are especially important in biology as they are involved in the Krebs citric acid cycle and in glycolysis...
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 pKa of 3.77. It can be prepared by the hydrolysis of the ethyl acetoacetateEthyl acetoacetate
The organic compound ethyl acetoacetate is the ethyl ester of acetoacetic acid. It is mainly 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; as well as...
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 rate
Reaction rate
The reaction rate or speed of reaction for a reactant or product in a particular reaction is intuitively defined as how fast or slow a reaction takes place...
to acetone
Acetone
Acetone is the organic compound with the formula 2CO, a colorless, mobile, flammable liquid, the simplest example of the ketones.Acetone is miscible with water and serves as an important solvent in its own right, typically as the solvent of choice for cleaning purposes in the laboratory...
and carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
:
- CH3C(O)CH2CO2H → CH3C(O)CH3 + CO2
The acid form has a half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
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
Ketone 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 acid
Beta-hydroxybutyrate
beta-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 acetone
Acetone
Acetone is the organic compound with the formula 2CO, a colorless, mobile, flammable liquid, the simplest example of the ketones.Acetone is miscible with water and serves as an important solvent in its own right, typically as the solvent of choice for cleaning purposes in the laboratory...
, 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
Conjugate acid
Within the Brønsted–Lowry acid-base theory , 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 chemical...
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.