Ketone halogenation
Encyclopedia
In organic chemistry
ketone halogenation is a special type of halogenation
.
The position alpha (next) to the carbonyl
group in a ketone
is easily halogenated, due to the ability to form an enolate in basic solution, or an enol
in acidic solution. An example is the bromination of acetone
in basic solution:
In acidic solution, usually only one alpha hydrogen is replaced by a halogen, because each successive halogenation is slower that the first. The halogen decreases the basicity of the carbonyl oxygen, thus making protonation less likely. However, in basic solution successive halogenations are more rapid, because the halogen withdraws electrons by induction and makes remaining hydrogens more acidic. In the case of methyl ketone
s, this results in what is called the haloform reaction
.
Organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, composition, reactions, and preparation of carbon-based compounds, hydrocarbons, and their derivatives...
ketone halogenation is a special type of halogenation
Halogenation
Halogenation is a chemical reaction that incorporates a halogen atom into a molecule in substitution of hydrogen atom. Halogenation takes place in the gas phase. There are four types of halogenation: fluorination, chlorination, bromination, and iodination...
.
The position alpha (next) to the carbonyl
Carbonyl
In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups....
group in a ketone
Ketone
In organic chemistry, a ketone is an organic compound with the structure RCR', where R and R' can be a variety of atoms and groups of atoms. It features a carbonyl group bonded to two other carbon atoms. Many ketones are known and many are of great importance in industry and in biology...
is easily halogenated, due to the ability to form an enolate in basic solution, or an enol
Enol
Enols are alkenes with a hydroxyl group affixed to one of the carbon atoms composing the double bond. Alkenes with a hydroxyl group on both sides of the double bond are called enediols. Deprotonated anions of enols are called enolates...
in acidic solution. An example is the bromination of 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...
in basic solution:
- CH3-CO-CH3 + OH− → CH3-CO-CH2− + H2O
- CH3-CO-CH2− + Br2 → CH3-CO-CH2Br + Br−
In acidic solution, usually only one alpha hydrogen is replaced by a halogen, because each successive halogenation is slower that the first. The halogen decreases the basicity of the carbonyl oxygen, thus making protonation less likely. However, in basic solution successive halogenations are more rapid, because the halogen withdraws electrons by induction and makes remaining hydrogens more acidic. In the case of methyl ketone
Ketone
In organic chemistry, a ketone is an organic compound with the structure RCR', where R and R' can be a variety of atoms and groups of atoms. It features a carbonyl group bonded to two other carbon atoms. Many ketones are known and many are of great importance in industry and in biology...
s, this results in what is called the haloform reaction
Haloform reaction
The haloform reaction is a chemical reaction where a haloform is produced by the exhaustive halogenation of a methyl ketone in the presence of a base. R may be , alkyl or aryl...
.