Question

Write the reaction involved in Etard reaction.

Hint:

Etard reaction converts the side-chain methyl group of aromatic compounds into an aldehyde using chromyl chloride.

Answer 1

Step 1: What the Etard reaction does.
The Etard reaction selectively oxidizes an aromatic methyl group ($-CH_3$) directly to an aldehyde ($-CHO$) using chromyl chloride ($CrO_2Cl_2$) in carbon disulphide ($CS_2$) as solvent.
Step 2: Mechanism outline.
$CrO_2Cl_2$ reacts with the methyl group to form a stable chromium complex (the Etard complex). Hydrolysis of this complex with water releases the aldehyde. The reaction stops at the aldehyde stage and does not proceed to the carboxylic acid.
Step 3: Reaction for toluene.
\[ C_6H_5CH_3 \xrightarrow[CS_2]{CrO_2Cl_2} \text{[Etard complex]} \xrightarrow{H_3O^+} C_6H_5CHO \] \[ \boxed{C_6H_5CH_3 \xrightarrow{CrO_2Cl_2/CS_2} C_6H_5CHO} \]