Question

Phenol is subjected to the following sequence of reactions: \[ \text{Phenol} \xrightarrow[\text{NaOH}]{\text{CO}_2} A \xrightarrow{\text{H}^+} B \xrightarrow[\text{Zn(Hg)}]{\text{Conc. HCl}} C \xrightarrow[\Delta]{NH_2NH_2/KOH} D \] If \(A\) is formed via Kolbe–Schmitt reaction and the final product \(D\) is obtained after the given sequence, then \(D\) is:

• A. Benzene
• B. Toluene
• C. Cyclohexane
• D. Phenol

Hint:

Important Named Reactions: Kolbe–Schmitt: \[ \text{Phenol} \rightarrow \text{Salicylic Acid} \] Clemmensen Reduction: \[ >C=O \rightarrow -CH_2- \] Wolff–Kishner Reduction: \[ >C=O \rightarrow -CH_2- \] These three reactions are among the most frequently tested organic reactions in CUET and NCERT-based examinations.

Answer 1

The Correct Option is A

Concept: This is a multi-concept reaction-sequence question involving:
• Kolbe–Schmitt reaction
• Functional group transformations
• Clemmensen reduction
• Wolff–Kishner reduction Such questions are particularly important for CUET because they test whether a student can connect multiple named reactions rather than recalling them individually.

Step 1: Identify the product of Kolbe–Schmitt reaction. Phenol reacts with sodium hydroxide to form sodium phenoxide. The sodium phenoxide reacts with carbon dioxide under pressure and heating. This is known as the: \[ \boxed{\text{Kolbe–Schmitt Reaction}} \] The major product formed is: \[ \text{o-Hydroxybenzoic acid} \] (commonly called salicylic acid after acidification). Thus: \[ A=\text{Sodium salicylate} \] and \[ B=\text{Salicylic acid} \]

Step 2: Examine the effect of Clemmensen reduction. Salicylic acid contains: \[ -COOH \] group. Under strong reduction conditions, the carbonyl-containing functionality is reduced. The net effect in this sequence is removal of the side-chain carbonyl functionality, leading toward the hydrocarbon framework.

Step 3: Analyze the Wolff–Kishner reduction step. Wolff–Kishner reduction converts: \[ >C=O \] into: \[ -CH_2- \] through hydrazone formation followed by base-induced elimination. After successive reductions, the oxygen-containing side chain is ultimately removed from the aromatic framework.

Step 4: Track the carbon skeleton carefully. The aromatic ring remains intact throughout the reaction sequence. The sequence progressively removes oxygenated functionalities attached to the ring. The final product is the parent aromatic hydrocarbon: \[ C_6H_6 \] which is benzene.

Step 5: Eliminate incorrect options. Option (B): Toluene would require introduction of a methyl group. No such step occurs. Option (C): Cyclohexane would require hydrogenation of the aromatic ring. Not present. Option (D): Phenol is the starting compound and is transformed during the sequence. Hence it cannot be the final product.

Step 6: Final conclusion. The final product is: \[ \boxed{\text{Benzene}} \] Therefore: \[ \boxed{\text{Option (A)}} \]