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 a significant organic process for the selective oxidation of aromatic methyl groups (\( -CH_3 \)) to aldehydes (\( -CHO \)) employing a specific oxidizing agent.
Step 1: Primary Reagent.
The principal reagent in the Etard reaction is chromyl chloride (\( \text{CrO}_2\text{Cl}_2 \)). This potent oxidizing agent transforms methyl groups on aromatic compounds, such as toluene, into formyl groups (\( -CHO \)), yielding benzaldehyde.
Step 2: Illustrative Reaction.
Specifically, when toluene (\( \text{C}_6\text{H}_5\text{CH}_3 \)) interacts with chromyl chloride in a solvent like carbon tetrachloride (\( \text{CCl}_4 \)), toluene's methyl group undergoes oxidation 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 exemplifies the Etard reaction's mechanism.
Conclusion:
Chromyl chloride \( \mathbf{(A)} \) is the correct reagent for the Etard reaction.