Aldehydes and Ketones - Methods of Preparation

1. From alkenes

2. From alkynes

3 From alcohols

4. From alkyl halides

5. From Grignard reagent

6. From carboxylic acids

7.From Acid chlorides

8.From alkyl cyanides

1. From alkenes

Alkenes react with ozone to form ozonide which on subsequent cleavage with zinc dust and water gives aldehydes and ketones.

2. From alkynes

Hydration of alkynes in the presence of dilute sulphuric acid and HgSO4 as catalyst gives aldehydes and ketones.

Water adds to alkynes to form unstable enol intermediates which rearrange to form aldehydes or ketones.

Hydration of acetylene gives acetaldehyde.

Hydration of alkynes other than acetylene gives ketones.


3. By oxidation of alcohols:

a) Primary alcohols on oxidation by potassium dichromate and dilute sulphuric acid give corresponding aldehyde

Potassium dichromate and sulphuric combine to give (0) nascent oxygen. Nascent oxygen oxidizes CH3OH to HCHO by removing H2 from CH3OH.

Nascent oxygen removes H2 from C2H5OH to give CH3CHO.

b)Ketones: Secondary alcohols on oxidation by potassium dichromate and dilute sulphuric acid mixture give ketones.

Isopropyl alcohol gives acetone.
2-butanol gives ethyl methyl ketone on oxidation.