Which of the following reagents convert an alcohol into an alkyl chloride?
(A) Conc. Hydrogen Chloride
(B) Phosphorus trichloride
(C) Phosphorus pentachloride
(D) Thionyl Chloride
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A), (B), (C) and (D)
Each of these reagents turns the poor leaving group –OH into a better one, and a chloride ion then takes its place.
(A) Conc. Hydrogen Chloride — Correct. Primary and secondary alcohols need anhydrous \( \ce{ZnCl2} \) as a catalyst (Lucas reagent); tertiary alcohols react on shaking with concentrated HCl at room temperature.
\( \displaystyle \ce{R-OH + HCl} \xrightarrow{\ce{ZnCl2}} \ce{R-Cl + H2O} \)
(B) Phosphorus trichloride — Correct. One molecule of \( \ce{PCl3} \) converts three molecules of alcohol, leaving phosphorous acid.
\( \displaystyle \ce{3R-OH + PCl3 -> 3R-Cl + H3PO3} \)
(C) Phosphorus pentachloride — Correct. The by-products are phosphoryl chloride and HCl.
\( \displaystyle \ce{R-OH + PCl5 -> R-Cl + POCl3 + HCl} \)
(D) Thionyl Chloride — Correct. The by-products are sulphur dioxide and HCl.
\( \displaystyle \ce{R-OH + SOCl2 -> R-Cl + SO2 ^ + HCl ^} \)
NCERT (2026-27 edition):
From Alcohols
