The reaction to obtain benzaldehyde from toluene by chromylchloride is :

Question

Accepted Answer

The reaction to obtain benzaldehyde from toluene using chromyl chloride is known as the Etard reaction. Here is a detailed explanation of why Option 3 is correct and why the other options are incorrect:

1. **Etard Reaction (Option 3)**:
   - The Etard reaction involves the oxidation of toluene to benzaldehyde using chromyl chloride (CrO2Cl2) as the oxidizing agent. In this reaction, chromyl chloride reacts with toluene to form a complex, which upon hydrolysis yields benzaldehyde. This is a well-established method for converting methyl groups attached to aromatic rings into aldehydes, specifically benzaldehyde in the case of toluene.

2. **Gatterman Reaction (Option 1)**:
   - The Gatterman reaction is used to form aromatic aldehydes from aromatic compounds using hydrogen cyanide (HCN) and hydrochloric acid (HCl) in the presence of a Lewis acid catalyst like aluminum chloride (AlCl3) or zinc chloride (ZnCl2). This reaction is not related to the use of chromyl chloride or the conversion of toluene to benzaldehyde.

3. **Gatterman-Koch Reaction (Option 2)**:
   - The Gatterman-Koch reaction is a method for formylation of aromatic compounds, where carbon monoxide (CO) and hydrochloric acid (HCl) are used in the presence of a Lewis acid catalyst to introduce a formyl group (-CHO) into the aromatic ring. This reaction does not involve chromyl chloride or the specific conversion of toluene to benzaldehyde.

4. **HVZ Reaction (Option 4)**:
   - The HVZ (Hell-Volhard-Zelinsky) reaction is a halogenation reaction used to convert carboxylic acids into α-halo carboxylic acids using halogens (like bromine) and phosphorus tribromide (PBr3). This reaction is unrelated to the oxidation of toluene to benzaldehyde and does not involve chromyl chloride.

In summary, the Etard reaction is the correct method for converting toluene to benzaldehyde using chromyl chloride, which is why Option 3 is the correct answer. The other options describe different reactions that do not achieve this specific transformation.