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:
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:
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. It is a hydrogen bond acceptor, but not a hydrogen bond donator, and can not hydrogen bond to itself. This makes ketones more volatile then 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
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
- ketone + organolithium reagent → lithium alkoxide
- lithium alkoxide + aqueous acid → tertiary alcohol
- ketone + alcohol + acid or base ↔ hemiacetal + water
Electrophilic addition
- ketone + electrophile → resonance stabilized cation
-
- 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
- ketone + [metal hydroxide] → alpha hydrogen deprotonation to yield carboanion. (i.e. CH3CHOCH2-)
Keto-enol tautomerism
- ketone + acid catalyst ↔ enol
Reactions at an α-carbon
- 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
See also
