The Hell-Volhard-Zelinsky reaction is used for preparing

Options

A. `beta`-halo acid
B. `lamda`-halo acid
C. `alpha`- halo acid
D. acid halide

Explanation

### Step-by-Step Solution:

1. **Understanding the Hell-Volhard-Zelinsky Reaction**:
The Hell-Volhard-Zelinsky (HVZ) reaction is a method for the halogenation of carboxylic acids, specifically at the alpha position (the carbon adjacent to the carboxyl group) when there is at least one alpha hydrogen present.

2. **Starting Material**:
The reaction begins with a carboxylic acid that has an alpha hydrogen. For example, let's consider acetic acid (CH3COOH).

3. **Reagents Used**:
The reagents typically used in this reaction are phosphorus (P) and bromine (Br2). The phosphorus reacts with bromine to form phosphorus tribromide (PBr3).

4. **Formation of Alpha Halogenated Product**:
The PBr3 reacts with the carboxylic acid. The oxygen of the carbonyl group (C=O) attacks the phosphorus atom, leading to the formation of an intermediate compound where bromine is added to the alpha carbon.

5. **Tautomerization**:
The intermediate can tautomerize to form an enol, which is a compound containing a double bond and an alcohol group. This enol form will have the bromine in the alpha position.

6. **Final Step - Hydrolysis**:
When water (H2O) is added, it attacks the alpha carbon, leading to the substitution of the alpha hydrogen with a bromine atom. This results in the formation of an alpha-bromo carboxylic acid.

7. **Conclusion**:
The final product of the Hell-Volhard-Zelinsky reaction is an alpha-halo carboxylic acid. For example, starting from acetic acid, the product would be alpha-bromoacetic acid (BrCH2COOH).

### Final Answer:
The Hell-Volhard-Zelinsky reaction is used for preparing **alpha-halo carboxylic acids**.

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