Question

Aniline is converted into benzene by the following sequence of reactions: \[ \text{Aniline} \xrightarrow[\text{0--5}^\circ C]{NaNO_2/HCl A \xrightarrow{H_3PO_2} B \] The compounds \(A\) and \(B\) respectively are:}

• A. Benzene diazonium chloride, Benzene
• B. Nitrobenzene, Benzene
• C. Benzene diazonium chloride, Phenol
• D. Chlorobenzene, Benzene

Hint:

Remember: \[ ArN_2^+Cl^- \xrightarrow{H_3PO_2} ArH \] Hypophosphorous acid replaces diazonium group by hydrogen.

Answer 1

The Correct Option is A

Concept: This question is based on:
• Diazotisation reaction
• Reduction of diazonium salts
• Important NCERT named reactions Primary aromatic amines react with nitrous acid at low temperature to form diazonium salts. Further reduction using hypophosphorous acid replaces diazonium group by hydrogen.

Step 1: Formation of diazonium salt. Aniline: \[ C_6H_5NH_2 \] reacts with: \[ NaNO_2 + HCl \] at: \[ 0-5^\circ C \] to form benzene diazonium chloride: \[ C_6H_5N_2^+Cl^- \] Thus: \[ A = \text{Benzene diazonium chloride} \] Reaction: \[ C_6H_5NH_2 \rightarrow C_6H_5N_2^+Cl^- \]

Step 2: Reduction of diazonium salt. Hypophosphorous acid: \[ H_3PO_2 \] reduces diazonium group into hydrogen. Thus: \[ C_6H_5N_2^+Cl^- \rightarrow C_6H_6 \] Hence: \[ B = \text{Benzene} \]

Step 3: Identify the correct option. Therefore: \[ A = \text{Benzene diazonium chloride} \] and \[ B = \text{Benzene} \] Hence correct option is: \[ \boxed{(A)} \]