Question

The reagent/s employed in Etard reaction is/are

• A. Cl\(_2\) hν, H\(_3\)O\(^+\)
• B. CrO\(_2\)Cl\(_2\) CS\(_2\), H\(_3\)O\(^+\)
• C. CO, HCl, anhydrous AlCl\(_3\) CuCl
• D. SnCl\(_2\), HCl
• E. DIBAL-H

Hint:

The Etard reaction is an alternative to side-chain chlorination followed by hydrolysis, but it directly gives the aldehyde.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
This is a question about a specific named reaction in organic chemistry. The Etard reaction is a method for the direct oxidation of an aromatic or heterocyclic bound methyl group to an aldehyde.
Step 2: Detailed Explanation:
The Etard reaction specifically refers to the oxidation of toluene (or its derivatives) to benzaldehyde using chromyl chloride (CrO\(_2\)Cl\(_2\)) as the oxidizing agent. The reaction is typically carried out in an inert, non-polar solvent such as carbon disulfide (CS\(_2\)) or carbon tetrachloride (CCl\(_4\)). This is followed by a hydrolysis step to yield the aldehyde. The reaction proceeds via the formation of a brown chromium complex, which prevents further oxidation of the aldehyde to a carboxylic acid.
Let's look at the other options:

(A) Cl\(_2\) / hv, H\(_2\)O\(^+\): This is free radical chlorination of the side chain of toluene, followed by hydrolysis. It can produce benzaldehyde, but it's not the Etard reaction.
(C) CO, HCl, anhydrous AlCl\(_3\) / CuCl: These are the reagents for the Gattermann-Koch reaction, used to formylate benzene.
(D) SnCl\(_2\), HCl: This reagent pair is used in the Stephen reduction, which converts nitriles to aldehydes.
(E) DIBAL-H: Diisobutylaluminium hydride is a reducing agent used, for example, to reduce esters or nitriles to aldehydes.
Step 3: Final Answer:
The reagents employed in the Etard reaction are chromyl chloride (CrO\(_2\)Cl\(_2\)) in an inert solvent like CS\(_2\), followed by hydrolysis. This corresponds to option (B).