How can the following conversions be brought about:
Benzoic acid to benzaldehyde.

Explanation

To convert benzoic acid to benzaldehyde, we can follow these steps:

### Step 1: Chlorination of Benzoic Acid
- **Reaction**: Benzoic acid (C6H5COOH) is treated with chlorine (Cl2) in the presence of a suitable catalyst, such as iron (Fe) or aluminum chloride (AlCl3). This results in the formation of chlorobenzoic acid.
- **Product**: Chlorobenzoic acid (C6H4ClCOOH) is formed.

### Step 2: Reduction of Chlorobenzoic Acid to Benzaldehyde
- **Reaction**: The chlorobenzoic acid is then subjected to reduction using Lindlar's catalyst (Pd on CaCO3 with lead acetate) in the presence of hydrogen gas (H2). This step selectively reduces the carboxylic acid group (COOH) to an aldehyde group (CHO).
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