The reaction of a primary alcohol with which of the following gives purely a haloalkane ?

Options

A. Phosphorus trichloride
B. Phosphorus pentachloride
C. Thionyl chloride
D. Sulphuryl chloride

Answer

To determine which reaction of a primary alcohol yields a purely haloalkane, we can analyze the reactions of primary alcohols with different reagents.

### Step-by-Step Solution:

1. **Identify the Nature of Primary Alcohols**:
A primary alcohol has the hydroxyl group (-OH) attached to a carbon that is only connected to one other carbon atom. This structure is crucial for determining the reaction pathway.

**Hint**: Remember that primary alcohols have the -OH group attached to a carbon that is only connected to one other carbon.

2. **Consider Reagents for Haloalkane Formation**:
Common reagents that can react with primary alcohols to form haloalkanes include:
- Hydrogen halides (e.g., HCl, HBr, HI)
- Thionyl chloride (SOCl2)
- Phosphorus trihalides (e.g., PCl3, PBr3)

**Hint**: Think about which reagents can replace the -OH group with a halogen atom.

3. **Analyze the Reaction with Thionyl Chloride (SOCl2)**:
The reaction of a primary alcohol with thionyl chloride produces a haloalkane and by-products (SO2 and HCl). The reaction can be represented as:
\[ R-OH + SOCl2 \rightarrow R-Cl + SO2 + HCl \]
This reaction yields a haloalkane (R-Cl) and is known for being efficient.

**Hint**: Thionyl chloride is a good reagent to produce haloalkanes from alcohols with minimal side products.

4. **Consider Phosphorus Halides**:
The reaction of a primary alcohol with phosphorus trihalides (like PCl3) also produces a haloalkane but may yield side products. The reaction can be represented as:
\[ R-OH + PCl3 \rightarrow R-Cl + H3PO3 \]
Here, H3PO3 is a side product, indicating that this reaction does not yield a purely haloalkane.

**Hint**: Phosphorus halides can produce side products, which may complicate the reaction.

5. **Conclusion**:
The reaction of a primary alcohol with thionyl chloride (SOCl2) is the best choice for obtaining a purely haloalkane without significant side products.

Therefore, the answer to the question is:
**Thionyl chloride (SOCl2)** gives purely a haloalkane when reacting with a primary alcohol.

### Final Answer:
**Thionyl chloride (SOCl2)** is the reagent that gives purely a haloalkane when reacting with a primary alcohol.