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.
Alternatively, toluene can be oxidised to aldehyde with chromium trioxide in acetic anhydride.
Side chain halogenation of toluene followed by hydrolysis yields aldehydes.
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.
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 :