Question

Aniline on treatment with NaNO\(_2\) and HCl at 278K gives compound (Y). When the compound (Y) is treated with Cu/HBr, compound 'Z' is obtained. The compound 'Z' is

• A. Benzene
• B. Benzene diazonium bromide
• C. Phenol
• D. Bromobenzene
• E. Chlorobenzene

Hint:

Sandmeyer reaction: ArN\(_2^+\)X\(^-\) + CuX → ArX + N\(_2\). CuCl gives chlorobenzene, CuBr gives bromobenzene, CuCN gives benzonitrile.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
This is a multi-step synthesis problem involving common reactions of aromatic compounds, specifically the reduction of a nitro group, diazotization of an amine, and a Sandmeyer-type reaction.
Step 2: Detailed Explanation:
Let's trace the reaction sequence step by step.
Step 1: Nitrobenzene to Compound (X)
Nitrobenzene (C\(_6\)H\(_5\)NO\(_2\)) is treated with Sn / HCl. This is a standard method for the reduction of a nitro group to a primary amino group. \[ \text{C}_6\text{H}_5\text{NO}_2 \xrightarrow{\text{Sn / HCl}} \text{C}_6\text{H}_5\text{NH}_2 \] So, compound (X) is Aniline.
Step 2: Compound (X) to Compound (Y)
Aniline (X) is treated with NaNO\(_2\) and HCl at a low temperature (273-278 K or 0-5 \(^\circ\)C). This reaction is called diazotization. It converts the primary aromatic amine into a diazonium salt. \[ \text{C}_6\text{H}_5\text{NH}_2 \xrightarrow{\text{NaNO}_2 \text{ / HCl, 278 K}} \text{C}_6\text{H}_5\text{N}_2^+\text{Cl}^- \] So, compound (Y) is Benzenediazonium chloride.
Step 3: Compound (Y) to Compound (Z)
Benzenediazonium chloride (Y) is treated with Cu / HBr. This is a variation of the Sandmeyer reaction (sometimes called the Gattermann reaction when copper powder is used instead of a cuprous salt). This reaction replaces the diazonium group (-N\(_2^+\)Cl\(^-\)) with a bromine atom from HBr. \[ \text{C}_6\text{H}_5\text{N}_2^+\text{Cl}^- \xrightarrow{\text{Cu / HBr}} \text{C}_6\text{H}_5\text{Br} + \text{N}_2 + \text{CuCl} \] So, the final compound (Z) is Bromobenzene.
Step 3: Final Answer:
The final compound 'Z' is Bromobenzene. This corresponds to option (D).