Ketone

Missing image Keton.png Keton group

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(CO)R₂.

A carbonyl carbon bonded to two carbon atoms distinguishes ketones from carboxylic acids, aldehydes, esters, amides, and other oxygen-containing compounds. The double bond of the carbonyl group distinguishes ketones from alcohols and ethers. The simplest ketone is acetone (also called propanone):

Missing image
Acetone.png
image:acetone.png

Contents

1 Structure 1.1 Carbonyl group 2 Nomenclature 2.1 IUPAC 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:

• Aldehydes.
• Carboxylic acids.
• Esters.

Nomenclature

IUPAC

In general ketones are named using IUPAC nomenclature by changing the suffix -e of the parent alkane to -one. For common ketones some traditional names such as acetone and benzophenone predominate, and these are considered retained IUPAC names (http://www.acdlabs.com/iupac/nomenclature/93/r93_701.htm), although some introductory chemistry texts use names such as 2-propanone or propanone.

Physical properties

A carbonyl group is polar. This makes ketones polar compounds. The carbonyl groups interact with water by hydrogen bonding. It is a hydrogen bond acceptor, but not a hydrogen bond donator, and can not hydrogen bond to itself. This makes ketones more volatile than alcohols or carboxylic acids of similar molecular weight

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

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

Electrophilic addition

1. ketone + electrophile → resonance stabilized cation

Wittig reaction

1. • ketone + phosphonium ylide → oxaphosphetane
     • oxaphosphetane → phosphine oxide + alkene

Other

1. ketone + water ↔ geminal diol
2. ketone + thiol + acid catalyst ↔ thioacetal + water
3. ketone + hydrazine or derivative of hydrazine → hydrazone
4. ketone + metal hydride → metal alkoxide salt
   • metal alkoxide salt + water → alcohol
5. ketone + [metal hydroxide] → alpha hydrogen deprotonation to yield carboanion. (i.e. CH3CHOCH2-)

Keto-enol tautomerism

1. ketone + acid catalyst ↔ enol
   • enol + halogen → α-haloketone

Reactions at an α-carbon

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

Ketones in medicine

Acetone, acetoacetate and beta-hydroxybutyrate are ketones (or ketone bodies) generated from carbohydrates, fatty acids and amino acids in humans and most vertebrates. Ketones are elevated in blood and urine in starvation, hypoglycemia due to causes other than hyperinsulinism, various inborn errors of metabolism and ketoacidosis (usually due to diabetes mellitus). Although ketoacidosis is characteristic of decompensated or untreated type 1 diabetes, ketosis or even ketoacidosis can occur in type 2 diabetes in some circumstances as well. 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.

Examples

• Acetophenone
• Butanone (methyl ethyl ketone)
• Propanone (acetone)

See also

• Diketone
• Aldehyde
• Ketosisda:Keton

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