The reaction of `Br_(2)//P or Cl_(2)//P` with carboxylic acid to form `alpha`- halogenated acid, is called

Options

A. Hunsdicker reaction
B. Hell - Vohlard - Zelinsky reaction
C. Claisen reaction
D. Kolbe's reaction

Answer

To solve the question regarding the reaction of bromine or chlorine with carboxylic acids to form alpha-halogenated acids, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Reactants**: The reactants in this reaction are carboxylic acids (e.g., acetic acid, CH₃COOH) and halogens (bromine, Br₂ or chlorine, Cl₂) in the presence of phosphorus (P).

2. **Understand the Reaction Mechanism**: When a carboxylic acid reacts with a halogen in the presence of phosphorus, the halogen replaces one of the hydrogen atoms on the alpha carbon (the carbon adjacent to the carboxyl group).

3. **Example of the Reaction**: For instance, if acetic acid (CH₃COOH) reacts with bromine (Br₂) in the presence of red phosphorus (P), the reaction will yield 2-bromoacetic acid (CH₂BrCOOH). The bromine replaces one of the hydrogen atoms on the alpha carbon.

4. **Naming the Reaction**: This specific reaction is known as the **Hell-Volhard-Zelinsky reaction**. It is a halogenation reaction that introduces a halogen atom at the alpha position of the carboxylic acid.

5. **Select the Correct Option**: Given the options, the correct name for the reaction is the **Hell-Volhard-Zelinsky reaction**.

### Final Answer:
The reaction of `Br₂` or `Cl₂` with carboxylic acid to form alpha-halogenated acid is called the **Hell-Volhard-Zelinsky reaction**.

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