Question

Identify the compound formed by action of chromyl chloride on toluene in presence of \(\text{CS}_2\) and hydrolysed further?

• A. Chlorobenzene
• B. Benzal chloride
• C. Benzaldehyde
• D. Benzoic acid

Hint:

Etard reaction is a selective oxidation that stops at aldehyde stage, unlike strong oxidizing agents which form benzoic acid.

Answer 1

The Correct Option is C

Concept:
The reaction of toluene with chromyl chloride \((\text{CrO}_2\text{Cl}_2)\) in a non–polar solvent like \(\text{CS}_2\) is known as the Etard reaction. It selectively oxidizes the methyl group \((-\text{CH}_3)\) attached to the benzene ring to an aldehyde group \((-\text{CHO})\) without further oxidation to acid. Step 1: Formation of Etard complex. Toluene reacts with chromyl chloride in \(\text{CS}_2\) to form a brown complex (Etard complex): \[ \text{C}_6\text{H}_5\text{CH}_3 \xrightarrow{\text{CrO}_2\text{Cl}_2 / \text{CS}_2} \text{Etard complex} \]
Step 2: Controlled oxidation. In this step, the benzylic \(-\text{CH}_3\) group is partially oxidized to \(-\text{CHO}\) group (aldehyde stage), not further to \(-\text{COOH}\).
Step 3: Hydrolysis of complex. On hydrolysis of the Etard complex: \[ \text{Etard complex} \xrightarrow{\text{H}_2\text{O}} \text{C}_6\text{H}_5\text{CHO} \]
Step 4: Identify the product. \[ \text{C}_6\text{H}_5\text{CHO} = \text{Benzaldehyde} \]
Step 5: Conclusion. Thus, the methyl group of toluene is converted into an aldehyde group: \[ \text{Toluene} \rightarrow \text{Benzaldehyde} \]