The best reagent for preparing an alkyl chloride from an alcohol is
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → \(SOCl_2\)
The best reagent is the one that gives the alkyl chloride free of other products. Thionyl chloride does this:
\( \displaystyle \ce{R-OH + SOCl2 -> R-Cl + SO2 ^ + HCl ^} \)
So \( \ce{SOCl2} \) is the best reagent.
Why the other options are incorrect
Option (1) Concentrated HCl — Incorrect. Primary and secondary alcohols need anhydrous \( \ce{ZnCl2} \) as catalyst, and water is formed, which must be removed:
\( \displaystyle \ce{R-OH + HCl} \xrightarrow{\ce{ZnCl2}} \ce{R-Cl + H2O} \)
Option (3) \(PCl_5\) — Incorrect. It gives the chloride along with phosphorus oxychloride, a liquid that has to be separated: \( \ce{R-OH + PCl5 -> R-Cl + POCl3 + HCl} \).
Option (4) \(PCl_3\) — Incorrect. It leaves phosphorous acid in the mixture: \( \ce{3R-OH + PCl3 -> 3R-Cl + H3PO3} \).
NCERT (2026-27 edition):
From Alcohols
