Question:
Identify the major products P and Q from the following set of reaction sequences:
Identify the major products P and Q from the following set of reaction sequences:
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Controlled oxidation of toluene gives benzaldehyde, while side-chain chlorination of toluene followed by hydrolysis can also give benzaldehyde.
Updated On: Jun 19, 2026
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The Correct Option is B
Solution and Explanation
Step 1: Identify the starting compound.
The starting compound is toluene, \(\mathrm{C_6H_5CH_3}\). It contains a methyl group attached to benzene ring.
Step 2: Formation of product P.
The reagent \(CrO_3/(CH_3CO)_2O\) at \(273K\), followed by hydrolysis, is used for controlled oxidation of the methyl group of toluene.
This reaction converts the side-chain methyl group \((-CH_3)\) into an aldehyde group \((-CHO)\).
\[ \mathrm{C_6H_5CH_3 \rightarrow C_6H_5CHO} \] Therefore, \[ P=\mathrm{C_6H_5CHO} \] which is benzaldehyde.
Step 3: Formation of product Q.
In the presence of \(Cl_2/h\nu\), toluene undergoes side-chain chlorination because the benzylic position is highly reactive under free-radical conditions.
Further hydrolysis with water at \(373K\) gives benzaldehyde.
\[ \mathrm{C_6H_5CH_3 \xrightarrow{Cl_2/h\nu} C_6H_5CHCl_2} \] \[ \mathrm{C_6H_5CHCl_2 \xrightarrow{H_2O,373K} C_6H_5CHO} \] Thus, \[ Q=\mathrm{C_6H_5CHO} \] which is benzaldehyde.
Step 4: Final conclusion.
Both reactions give benzaldehyde as the major product.
\[ \boxed{P=\text{Benzaldehyde},\quad Q=\text{Benzaldehyde}} \]
The starting compound is toluene, \(\mathrm{C_6H_5CH_3}\). It contains a methyl group attached to benzene ring.
Step 2: Formation of product P.
The reagent \(CrO_3/(CH_3CO)_2O\) at \(273K\), followed by hydrolysis, is used for controlled oxidation of the methyl group of toluene.
This reaction converts the side-chain methyl group \((-CH_3)\) into an aldehyde group \((-CHO)\).
\[ \mathrm{C_6H_5CH_3 \rightarrow C_6H_5CHO} \] Therefore, \[ P=\mathrm{C_6H_5CHO} \] which is benzaldehyde.
Step 3: Formation of product Q.
In the presence of \(Cl_2/h\nu\), toluene undergoes side-chain chlorination because the benzylic position is highly reactive under free-radical conditions.
Further hydrolysis with water at \(373K\) gives benzaldehyde.
\[ \mathrm{C_6H_5CH_3 \xrightarrow{Cl_2/h\nu} C_6H_5CHCl_2} \] \[ \mathrm{C_6H_5CHCl_2 \xrightarrow{H_2O,373K} C_6H_5CHO} \] Thus, \[ Q=\mathrm{C_6H_5CHO} \] which is benzaldehyde.
Step 4: Final conclusion.
Both reactions give benzaldehyde as the major product.
\[ \boxed{P=\text{Benzaldehyde},\quad Q=\text{Benzaldehyde}} \]
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