You can't directly convert aniline (C₆H₅NH₂) into chlorobenzene (C₆H₅Cl) with a single reagent. This is because the amino group (-NH₂) is a strong activating group in electrophilic aromatic substitution reactions, making it difficult to replace it with chlorine.

Here's a breakdown of the problem and a potential solution:

The Problem:

* Direct chlorination: Direct chlorination of aniline would lead to multiple chlorination at the ortho and para positions to the amino group due to its strong activating nature.

* Direct replacement: Replacing the amino group directly with chlorine is not a straightforward reaction.

Solution: A Multi-Step Approach

1. Diazotization: Treat aniline with nitrous acid (HNO₂) in the presence of a strong acid (like HCl) at low temperatures (0-5°C). This reaction forms a diazonium salt:

```

C₆H₅NH₂ + HNO₂ + HCl → [C₆H₅N₂⁺]Cl⁻ + 2H₂O

```

2. Sandmeyer Reaction: The diazonium salt is then reacted with cuprous chloride (CuCl) in the presence of hydrochloric acid. This replaces the diazonium group with chlorine, yielding chlorobenzene:

```

[C₆H₅N₂⁺]Cl⁻ + CuCl + HCl → C₆H₅Cl + N₂ + CuCl₂

```

Important Considerations:

* Diazonium salts are unstable: They must be prepared and used immediately.

* Reaction conditions: The Sandmeyer reaction requires specific conditions for optimal yield.

* Alternative methods: There are other methods to synthesize chlorobenzene, but they are not as common.

Let me know if you have any further questions!