Which one of the following reactions can be used for the preparation of `beta` - hydroxy acid

Options

A. Perkin reaction
B. Reformatsky reaction
C. Aldol condensation
D. Claisen condensation

Answer

To determine which reaction can be used for the preparation of beta-hydroxy acid, we will analyze each option provided in the question:

### Step-by-Step Solution:

1. **Understand the Concept of Beta-Hydroxy Acid:**
- A beta-hydroxy acid is a compound that contains a hydroxyl group (-OH) on the beta carbon relative to the carboxylic acid group (-COOH).

2. **Analyze the Options:**
- **Option A: Perkin Reaction**
- The Perkin reaction involves the condensation of an aromatic aldehyde with an anhydride in the presence of a base to form alpha, beta-unsaturated aromatic acids. This does not yield beta-hydroxy acids.
- **Conclusion:** Incorrect.

- **Option B: Reformatsky Reaction**
- The Reformatsky reaction involves the reaction of an alpha-halo ester with zinc, leading to the formation of a beta-hydroxy acid after hydrolysis. The product formed has a hydroxyl group on the beta carbon, making it a beta-hydroxy acid.
- **Conclusion:** Correct.

- **Option C: Aldol Condensation**
- Aldol condensation involves the reaction between aldehydes or ketones to form beta-hydroxy aldehydes or ketones, but the reaction typically leads to the formation of alpha, beta-unsaturated carbonyl compounds upon dehydration. Hence, it does not specifically yield beta-hydroxy acids.
- **Conclusion:** Incorrect.

- **Option D: Claisen Condensation**
- Claisen condensation involves the reaction of esters in the presence of a base to form beta-keto esters. While it does involve the formation of a beta compound, it does not yield beta-hydroxy acids.
- **Conclusion:** Incorrect.

3. **Final Conclusion:**
- The only reaction that can be used for the preparation of beta-hydroxy acid is the **Reformatsky Reaction (Option B)**.

### Final Answer:
**B) Reformatsky Reaction**