Summary of Preparations
Aldehydes and Ketones
Like aldehydes, ketones can be prepared in a number of ways. The following sections detail some of the more common preparation methods: the oxidation of secondary alcohols, the hydration of alkynes, the ozonolysis of alkenes, Friedel-Crafts acylation, the use of lithium dialkylcuprates, and the use of a Grignard reagent.
Oxidation of secondary alcohols
The oxidation of secondary alcohols to ketones may be carried out using strong oxidizing agents, because further oxidation of a ketone occurs with great difficulty. Normal oxidizing agents include potassium dichromate (K2Cr2O7) and chromic acid (H2CrO4). The conversion of 2-propanol to 2-propanone illustrates the oxidation of a secondary alcohol.
|
Hydration of alkynes
The addition of water to an alkyne leads to the formation of an unstable vinyl alcohol. These unstable materials undergo keto-enol tautomerization to form ketones. The hydration of propyne forms 2-propanone, as the following figure illustrates.
|
Ozonolysis of alkenes
When one or both alkene carbons contain two alkyl groups, ozonolysis generates one or two ketones. The ozonolysis of 1,2-dimethyl propene produces both 2-propanone (a ketone) and ethanal (an aldehyde).
|
Friedel-Crafts acylation
Friedel-Crafts acylations are used to prepare aromatic ketones. The preparation of acetophenone from benzene and acetyl chloride is a typical Friedel-Crafts acylation.
|
Lithium dialkylcuprates
The addition of a lithium dialkylcuprate (Gilman reagent) to an acyl chloride at low temperatures produces a ketone. This method produces a good yield of acetophenone.
|
Grignard reagents
Hydrolysis of the salt formed by reacting a Grignard reagent with a nitrile produces good ketone yields. For example, you can prepare acetone by reacting the Grignard reagent methyl magnesium bromide (CH3MgBr) with methyl nitrile (CH3CN).
|
