Ketone

A ketone is either the functional group characterized by a carbonyl group linked to two other carbon atoms or a compound that contains this functional group. A ketone can be generally represented by the formula:

R₁(C O)R₂.

Among the other oxygen-containing compounds, the fact that ketones feature a carbonyl carbon bonded to two carbon atoms distinguishes them from carboxylic acids, aldehydes, esters, and amides. The double-bonded nature of the carbonyl group distinguishes ketones from alcohols and ethers. The smallest ketone is acetone:

Contents

3 Physical properties

3.1 Spectroscopic properties

4 Reactions

4.1 Synthesis
4.2 Reactions

4.2.1 Nucleophilic addition
4.2.2 Electrophilic addition
4.2.3 Wittig reaction
4.2.4 Other

4.3 Keto-enol tautomerism
4.4 Reactions at an α-carbon

5 Ketones in medicine

6 Ketones in perfume

7 Examples

8 See also

Structure

The ketone functional group is a carbonyl group bonded to two carbon atoms.

Carbonyl group

A carbonyl group consists of a carbon atom doubly bonded to an oxygen atom.

A carbon atom adjacent to a carbonyl group is called an α carbon. Hydrogens attached to this carbon are called α hydrogens.

The carbonyl group is also found in:

Nomenclature

IUPAC

Ketones are named using IUPAC nomenclature by changing the suffix -e of the parent alkane to -one.

Physical properties

A carbonyl group is polar. This makes ketones polar compounds. The carbonyl groups interact with water by hydrogen bonding.

Spectroscopic properties

Spectroscopy is an important means for identifying ketones.

Reactions

Synthesis

Ketones can be created by oxidation of secondary alcohols. The process requires a strong oxidising agent such as potassium dichromate or other reagent containing Cr(VI). The alcohol is oxidised by heating under reflux in acidified solution. For example 2-propanol is oxidised to propanone (acetone):

H₃C-CH(OH)-CH₃ → H₃C-CO-CH₃

Two atoms of hydrogen are removed, leaving a single oxygen atom double bonded to a carbon atom.

Reactions

Nucleophilic addition

ketone + nucleophile → tetrahedral carbonyl addition compound

ketone + anion of terminal alkyne → tetrahedral carbonyl addition compound (alkoxide)
- alkoxide + aqueous acid → hydroxyalkyne
ketone + ammonia or primary amine ↔ tetrahedral carbonyl addition compound
- tetrahedral carbonyl addition compound + acid catalyst → imine + water
ketone + secondary amine ↔ tetrahedral carbonyl addition compound
- tetrahedral carbonyl addition compound + acid catalyst → enamine + water
ketone + Grignard reagent → magnesium alkoxide
- magnesium alkoxide + aqueous acid → tertiary alcohol
ketone + organolithium reagent → lithium alkoxide
- lithium alkoxide + aqueous acid → tertiary alcohol
ketone + alcohol + acid or base ↔ hemiacetal + water
- hemiacetal + alcohol + acid catalyst ↔ acetal + water
- This is a carbonyl-protecting reaction.

Electrophilic addition

ketone + electrophile → resonance stabilized cation

Wittig reaction

- ketone + phosphonium ylide → oxphosphetane
  - oxphosphetane → phosphine oxide + alkene

Other

ketone + water ↔ geminal diol
ketone + thiol + acid catalyst ↔ thioacetal + water
ketone + hydrazine or derivative of hydrazine → hydrazone
ketone + metal hydride → metal alkoxide salt
- metal alkoxide salt + water → alcohol

Keto-enol tautomerism

ketone + acid catalyst ↔ enol
- enol + halogen → α-haloketone

Reactions at an α-carbon

ketone + aqueous deuterium + D⁺ or OD^- catalyst → ketone-d + HOD

Ketones in medicine

Ketones (or ketone bodies) are a breakdown product of fatty acids and are elevated (in blood or urine samples) in starvation, hypoglycemia due to causes other than hyperinsulinism, and some acute cases of diabetes mellitus (typically type 1, but in some circumstances type 2 as well). These ketones are acetone, acetoacetate and beta-hydroxybutyrate. Acetoacetate and beta-hydroxybutyrate are an important fuel for many tissues, especially during fasting and starvation. The brain, in particular, relies heavily on ketone bodies during times of reduced food intake.

Ketones in perfume

Ketones are often used in perfumes and paints to stabilize the other ingredients so that they don't degrade over time as quickly.