Question

What are Etard Reaction and Gattermann Koch Reaction? Give example.

Answer 1

Aromatic aldehydes (benzaldehyde and its derivatives) are prepared from aromatic hydrocarbons by Etard and Gattermann Koch's reaction.

Etard reaction

• In this reaction, chromyl chloride $\left({\mathrm{CrO}}_2{\mathrm{Cl}}_2\right)$is used.
• In this reaction, chromyl chloride oxidizes the methyl group to a chromium complex, which on hydrolysis yields the corresponding benzaldehyde.

Example of Etard reaction

• With chromyl chloride, toluene and all other homologs of benzene are oxidized to aldehydes in which the terminal carbon atom forms an aldehyde functional group. Toluene would get oxidized to benzaldehyde using the Etard reaction.
  

Gattermann Koch Reaction

• Gattermann Koch Reaction Mechanism begins with the formation of the reactive species with the help of the acid. The overall aim of the reaction is to attach a formyl group (-CHO group) to an aromatic system.

Example of Gattermann reaction

• When benzene reacts with carbon monoxide and hydrogen chloride in the presence of cuprous chloride or anhydrous aluminum chloride, the formation of benzaldehyde takes place.
• The reaction is as follows:-