Alkyl halides are prepared from alcohols, which are easily accessible. The hydroxyl group of an alcohol is replaced by halogen on reactions with certain compounds. Which one of the below compounds is inappropriate as a reagent ?

Options

A. Concentrated halogen acid
B. Sodium dihalide
C. Thionyl chloride
D. Phosphorus halides

Answer

To determine which compound is inappropriate as a reagent for converting alcohols to alkyl halides, we will analyze the given options based on their reactivity and suitability for this type of reaction.

### Step-by-Step Solution:

1. **Understanding the Reaction**:
- Alcohols (ROH) can be converted to alkyl halides (R-X) by replacing the hydroxyl group (-OH) with a halogen (X).
- Common reagents for this conversion include concentrated halogen acids (like HCl, HBr, HI), thionyl chloride (SOCl2), and phosphorus halides (PCl3, PCl5).

2. **Evaluating the Options**:
- **Concentrated Halogen Acids**: These are suitable reagents for converting alcohols to alkyl halides. They provide the halogen in a reactive form.
- **Sodium Halides**: Sodium halides (like NaCl, NaBr) are not typically used for this conversion because they do not provide a reactive halogen species that can replace the hydroxyl group. Instead, they are salts and do not participate in the reaction in the same way as acids or chlorides.
- **Thionyl Chloride (SOCl2)**: This is a well-known reagent for converting alcohols to alkyl chlorides and is appropriate for this reaction.
- **Phosphorus Halides (PCl3, PCl5)**: These are also suitable reagents for converting alcohols to alkyl halides.

3. **Identifying the Inappropriate Reagent**:
- Among the options, sodium halides are inappropriate as they do not effectively convert alcohols to alkyl halides. They lack the reactivity needed for this transformation.

### Conclusion:
The inappropriate reagent for converting alcohols to alkyl halides is **sodium halides**.