Question

The reagent used in the Etard reaction is:

• A. $\text{Chromyl chloride (CrO}_2\text{Cl}_2)$
• B. $\text{Potassium dichromate (K}_2\text{Cr}_2\text{O}_7)$
• C. $\text{Chromic acid (H}_2\text{CrO}_4)$
• D. $\text{Sodium dichromate (Na}_2\text{Cr}_2\text{O}_7)$

Hint:

The \textbf{Etard reaction} is a useful method for preparing \textbf{benzaldehyde} from \textbf{methyl-substituted aromatic compounds}. It utilizes \textbf{chromyl chloride} ($\text{CrO}_2\text{Cl}_2$) as the key oxidizing agent, which is effective in oxidizing methyl groups to formyl groups.

Answer 1

The Correct Option is A

The Etard reaction is an important organic reaction that selectively oxidizes aromatic methyl groups ($-CH_3$) into aldehydes ($-CHO$) using a specific oxidizing agent.
Step 1: Key Reagent in the Etard Reaction.
The key reagent used in the Etard reaction is chromyl chloride ($\text{CrO}_2\text{Cl}_2$). This compound is a strong oxidizing agent that is used to convert methyl groups on aromatic compounds, such as toluene, into formyl groups ($-CHO$) to form benzaldehyde.
Step 2: Example Reaction.
For instance, when toluene ($\text{C}_6\text{H}_5\text{CH}_3$) reacts with chromyl chloride in a solvent like carbon tetrachloride ($\text{CCl}_4$), the methyl group of toluene is oxidized to form benzaldehyde ($\text{C}_6\text{H}_5\text{CHO}$): $$\text{C}_6\text{H}_5\text{CH}_3 + \text{CrO}_2\text{Cl}_2 \rightarrow \text{C}_6\text{H}_5\text{CHO}.$$ This is a typical example of how the Etard reaction works.
Conclusion:
The correct reagent used in the Etard reaction is chromyl chloride $\mathbf{(A)}$.