Preparation of Aromatic Aldehydes and Ketones

Preparation of Aromatic Aldehydes

Toluene (methylbenzene) is oxidised to chromium complex with a solution of chromyl chloride (CrO₂Cl₂) in CCl₄ or CS₂, which on hydrolysis gives aldehyde. Preparation of aldehydes by this method is known as Etard process.

Benzaldehyde is prepared by etard process

Alternatively, toluene can be oxidised to aldehyde with chromium trioxide in acetic anhydride.

preparation of benzaldehyde from toluene

Side chain halogenation of toluene followed by hydrolysis yields aldehydes.

Preparation of aromatic aldehydes by halogenation

Benzene is treated with CO and HCl in the presence of lewis acid like anhydrous AlCl₃ to give benzaldehyde. Preparation of aldehydes by this method is known as Gatterman-Koch reaction.

Preparation of benzaldehyde by gatterman-Koch reaction

Preparation of Aromatic Ketones

Friedal-Crafts acylation is one of the most convenient methods for the preparation of aromatic ketones. Friedal-Crafts acylation reaction involves the treatment of benzene or substituted benzene with acid chloride or acid anhydride in the presence of a lewis acid such as anhydrous AlCl₃ to form corresponding ketones.

Acid anhydride is used in the following example :

preparation of ketones by friedel Crafts reaction

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