Starting from aniline how will you prepare benzene diazonium chloride and chlorobenzene from the later? Explain giving chemical reactions involved.

To prepare benzene diazonium chloride from aniline and subsequently convert it to chlorobenzene, you need to follow two steps: diazotization and Sandmeyer reaction.

Step 1: Preparation of Benzene Diazonium Chloride (Diazotization)
Aniline (C₆H₅NH₂) reacts with nitrous acid (HNO₂) in the presence of hydrochloric acid (HCl) at a low temperature (0-5°C) to form benzene diazonium chloride (C₆H₅N₂⁺Cl⁻). Nitrous acid is typically generated in situ by reacting sodium nitrite (NaNO₂) with HCl.

Reaction:
C₆H₅NH₂ (Aniline) + NaNO₂ + 2HCl → C₆H₅N₂⁺Cl⁻ (Benzene Diazonium Chloride) + NaCl + 2H₂O

In this reaction:

Aniline is converted to benzene diazonium chloride.
The reaction requires low temperatures (0-5°C) to stabilize the diazonium salt.
Step 2: Preparation of Chlorobenzene (Sandmeyer Reaction)
Benzene diazonium chloride can be converted to chlorobenzene (C₆H₅Cl) using a copper(I) chloride (CuCl) catalyst. This is an example of a Sandmeyer reaction, where the diazonium group (–N₂⁺) is replaced by a chlorine atom.

Reaction:
C₆H₅N₂⁺Cl⁻ + CuCl → C₆H₅Cl (Chlorobenzene) + N₂ (Nitrogen gas)

In this reaction:

The benzene diazonium chloride reacts with CuCl to produce chlorobenzene and nitrogen gas is liberated as a by-product.
Summary of Reactions:
Diazotization: C₆H₅NH₂ + NaNO₂ + 2HCl → C₆H₅N₂⁺Cl⁻ + NaCl + 2H₂O

Sandmeyer Reaction: C₆H₅N₂⁺Cl⁻ + CuCl → C₆H₅Cl + N₂

Thus, starting from aniline, you can prepare benzene diazonium chloride, which can be further used to obtain chlorobenzene through the Sandmeyer reaction.