Question

The best method for the conversion of an alcohol into an alkyl chloride is by treating the alcohol with:

• A. PCl\(_5\)
• B. PCl\(_3\)
• C. SOCl\(_2\) in presence of pyridine
• D. dry HCl in the presence of anhydrous ZnCl\(_2\)

Hint:

Thionyl chloride is preferred for converting alcohols to alkyl chlorides because its gaseous by-products make the reaction clean and irreversible.

Answer 1

The Correct Option is C

Step 1: Identify the most suitable reagent for converting alcohols to alkyl chlorides. Among the given reagents, \(\text{SOCl}_2\) (thionyl chloride) in presence of pyridine is considered the best reagent for this conversion. Step 2: Reason for using thionyl chloride. The reaction proceeds as: \[ \text{ROH} + \text{SOCl}_2 \rightarrow \text{RCl} + \text{SO}_2 + \text{HCl} \] The by-products \(\text{SO}_2\) and \(\text{HCl}\) are gases and escape from the reaction mixture, driving the reaction to completion. Step 3: Role of pyridine. Pyridine:

Acts as a base to absorb HCl,
Prevents side reactions,
Increases the yield of alkyl chloride.
Step 4: Comparison with other reagents.

PCl\(_5\) and PCl\(_3\) produce solid or liquid by-products, making purification difficult.
Dry HCl with ZnCl\(_2\) (Lucas reagent) is less effective and mainly used for classification of alcohols.
Thus, the best method is using \(\boxed{\text{SOCl}_2}\) in presence of pyridine.