In the preparation of alkyl halide from alcohol which of the following reagent is preferred?

Options

A. `HX+ZnCl_(2)`
B. `PX_(3)`
C. `PCl_(5)`
D. `SOCl_(2)`

Answer

To determine the preferred reagent for the preparation of alkyl halides from alcohols, we will analyze the options provided and their reactions with alcohols.

### Step-by-Step Solution:

1. **Identify the Reagents**: The question provides four different reagents that can be used to convert alcohols (ROH) into alkyl halides (R-X). The reagents are:
- HX (where X is a halogen)
- PX3 (where P is phosphorus and X is a halogen)
- PCl5 (phosphorus pentachloride)
- SOCl2 (thionyl chloride)

2. **Analyze Each Reagent**:
- **Option 1: HX (Hydrogen Halide)**:
- Reaction: ROH + HX → R-X + H2O
- Side Products: Water
- This reaction produces an alkyl halide but generates water as a byproduct, which may complicate purification.

- **Option 2: PX3 (Phosphorus Halide)**:
- Reaction: ROH + PX3 → R-X + H3PO3 (phosphorous acid)
- Side Products: Phosphorous acid
- This reaction also produces an alkyl halide but generates a liquid byproduct, which may require further purification.

- **Option 3: PCl5 (Phosphorus Pentachloride)**:
- Reaction: ROH + PCl5 → R-Cl + POCl3 + HCl
- Side Products: Phosphoryl chloride (POCl3) and HCl
- This reaction produces an alkyl halide, but the byproducts are also liquids, which complicate the purification process.

- **Option 4: SOCl2 (Thionyl Chloride)**:
- Reaction: ROH + SOCl2 → R-Cl + SO2 + HCl
- Side Products: Sulfur dioxide (SO2) and HCl
- This reaction produces an alkyl halide, and the byproducts include gases (SO2 and HCl), which can escape from the reaction mixture.

3. **Determine the Preferred Reagent**:
- The key factor in choosing the preferred reagent is the nature of the side products. In the fourth option (SOCl2), the side products are gases (SO2 and HCl), which will escape from the reaction mixture. This means that the alkyl halide produced will be purer and will not require additional purification steps.
- Therefore, the preferred reagent for the preparation of alkyl halides from alcohols is **Option 4: SOCl2**.

### Final Answer:
**The preferred reagent for the preparation of alkyl halides from alcohol is SOCl2 (thionyl chloride).**

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