p-Chlorobenzoic acid can be prepared by reacting p-aminobenzoic acid with

Options

A. HCl
B. `Cu_(2)Cl_(2)`
C. `Cl_(2)` in presence of `AlCl_(3)`
D. `HNO(2)`, followed by hot solution of `Cu_(2)Cl_(2)`.

Answer

To prepare p-chlorobenzoic acid from p-aminobenzoic acid, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Starting Material**: We start with p-aminobenzoic acid, which has the structure:
- Benzene ring with an amino group (-NH2) at the para position relative to the carboxylic acid group (-COOH).

2. **Understand the Reaction**: The goal is to replace the amino group (-NH2) with a chlorine atom (-Cl) to form p-chlorobenzoic acid.

3. **Use of HNO2**: The first step involves treating p-aminobenzoic acid with nitrous acid (HNO2). This reaction leads to the formation of a diazonium salt:
- The amino group (-NH2) is converted to a diazonium group (-N2+), resulting in the formation of p-diazobenzenecarboxylic acid.

4. **Formation of Diazotization Product**: The reaction can be represented as:
- p-aminobenzoic acid + HNO2 → p-diazobenzenecarboxylic acid (with -N2+ group).

5. **Use of Cu2Cl2**: The next step is to treat the diazonium compound with a hot solution of copper(I) chloride (Cu2Cl2):
- The diazonium group (-N2+) is replaced by a chlorine atom (-Cl) in a reaction known as the Sandmeyer reaction.

6. **Final Product Formation**: The final product after the reaction is p-chlorobenzoic acid, which has the structure:
- Benzene ring with a carboxylic acid group (-COOH) and a chlorine atom (-Cl) at the para position.

### Conclusion:
The correct reagent to convert p-aminobenzoic acid to p-chlorobenzoic acid is **HNO2 followed by hot Cu2Cl2**.