`-OH` can be replaced by -Cl if we use

Options

A. `PCl_(5)`
B. `PCl_(3)`
C. `SOCl_(2)`
D. none of the above

Answer

To determine which reagent can replace the -OH group with -Cl, we will analyze the three given reagents: PCl5, PCl3, and SOCl2.

### Step-by-Step Solution:

1. **Understanding the Reaction**:
The -OH group in alcohols can be replaced by -Cl through a nucleophilic substitution reaction. The reagents we are considering are phosphorus pentachloride (PCl5), phosphorus trichloride (PCl3), and thionyl chloride (SOCl2).

2. **Using PCl5**:
- When an alcohol (e.g., ethanol, CH3CH2OH) reacts with PCl5, the lone pair of electrons on the oxygen atom of the -OH group attacks the phosphorus atom in PCl5.
- This leads to the formation of an intermediate where one chlorine atom is released, resulting in the formation of an alkyl chloride (e.g., CH3CH2Cl) and phosphorus oxychloride (POCl3).
- Therefore, PCl5 can effectively replace -OH with -Cl.

3. **Using PCl3**:
- In the case of PCl3, the mechanism is similar. The -OH group attacks the phosphorus atom, and one chlorine atom is displaced.
- This results in the formation of an alkyl chloride (RCl) and phosphorous acid (H3PO3).
- Thus, PCl3 can also replace -OH with -Cl.

4. **Using SOCl2**:
- When an alcohol reacts with SOCl2, the oxygen atom of the -OH group attacks the sulfur atom in SOCl2.
- This results in the formation of an intermediate where one chlorine atom is released, leading to the formation of an alkyl chloride (RCl) and sulfur dioxide (SO2) along with HCl.
- Therefore, SOCl2 can also replace -OH with -Cl.

5. **Conclusion**:
All three reagents (PCl5, PCl3, and SOCl2) can replace the -OH group with -Cl.

### Final Answer:
- The -OH group can be replaced by -Cl using PCl5, PCl3, or SOCl2.