Question

An organic compound "A" reacts with \( \text{Zn}/\text{Hg} / \text{Conc. HCl} \) to form p-Xylene. It reduces Tollen's reagent and on oxidation with \( \text{KMnO}_4 / H^+ \) it yields 1,4-benzenedicarboxylic acid. Identify compound A.

• A. \( \text{p-methylbenzaldehyde} \)
• B. \( \text{p-Cresol} \)
• C. \( \text{m-Cresol} \)
• D. \( 4 \)-Methylacetophenone

Hint:

The Clemmensen reduction reduces an aldehyde to a methyl group, and Tollen's reagent can be used to identify aldehydes. Oxidation with \( \text{KMnO}_4 \) leads to the formation of carboxylic acids.

Answer 1

The Correct Option is A

Step 1: Identify the first reaction with \( \text{Zn}/\text{Hg} / \text{Conc. HCl} \).
The reaction with \( \text{Zn}/\text{Hg} \) in the presence of concentrated HCl is a classic Clemmensen reduction, which reduces the aldehyde group (\( \text{-CHO} \)) to a methyl group (\( \text{-CH}_3 \)). The starting material is \( \text{p-methylbenzaldehyde} \), which is reduced to \( \text{p-xylene} \) (1,4-dimethylbenzene).
\[ \text{p-methylbenzaldehyde} \xrightarrow{\text{Zn}/\text{Hg}, \text{Conc. HCl}} \text{p-xylene} \]

Step 2: Analyze the reaction with Tollen's reagent.
Tollen's reagent is used to detect aldehydes. It reduces the aldehyde group in \( \text{p-methylbenzaldehyde} \), confirming the presence of the aldehyde functional group.

Step 3: Oxidation with \( \text{KMnO}_4 / H^+ \).
On oxidation with \( \text{KMnO}_4 / H^+ \), the methyl group in \( \text{p-xylene} \) is oxidized to a carboxyl group, resulting in the formation of 1,4-benzenedicarboxylic acid, confirming the structure of \( \text{p-methylbenzaldehyde} \).

Step 4: Conclusion.
Based on the reactions described, compound A is \( \text{p-methylbenzaldehyde} \), which reacts as described to yield the correct product. Therefore, the correct answer is option (A).