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. Let's delve into why Option 3 is the correct answer and why the other options are incorrect.

1. **Etard Reaction (Option 3):**
   - The Etard reaction is a specific chemical reaction used to oxidize toluene to benzaldehyde. In this reaction, toluene is treated with chromyl chloride (CrO2Cl2) in a non-polar solvent like carbon tetrachloride (CCl4). The chromyl chloride acts as an oxidizing agent, converting the methyl group of toluene into an aldehyde group, resulting in the formation of benzaldehyde. This reaction is well-documented and widely recognized in organic chemistry for this specific transformation, which is why Option 3 is the correct answer.

2. **Gatterman Reaction (Option 1):**
   - The Gatterman reaction is used to form aromatic aldehydes from aromatic compounds by using hydrogen cyanide (HCN) and hydrochloric acid (HCl) in the presence of a Lewis acid catalyst like aluminum chloride (AlCl3). This reaction is not used for the oxidation of toluene to benzaldehyde, making Option 1 incorrect in this context.

3. **Gatterman Koch Reaction (Option 2):**
   - The Gatterman Koch reaction is a variation of the Gatterman reaction, used to form aromatic aldehydes from benzene or its derivatives using carbon monoxide (CO) and hydrochloric acid (HCl) in the presence of a Lewis acid catalyst. This reaction does not involve the use of chromyl chloride or the oxidation of toluene, thus making Option 2 incorrect for the given transformation.

4. **HVZ Reaction (Option 4):**
   - The HVZ (Hell-Volhard-Zelinsky) reaction is a halogenation reaction used to convert carboxylic acids into α-halo acids. It involves the use of phosphorus tribromide (PBr3) and bromine (Br2). This reaction is unrelated to the oxidation of toluene to benzaldehyde and does not involve chromyl chloride, making Option 4 incorrect.

In conclusion, 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.