Which of the following reagents converts ethanol into bromoethane?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Phosphorus tribromide
To make bromoethane, the C–O bond of ethanol must break and the –OH group must be replaced by bromine. Phosphorus tribromide does this, converting alcohols to alkyl bromides:
\( \displaystyle \ce{3C2H5OH + PBr3 -> 3C2H5Br + H3PO3} \)
Why the other options are incorrect
Option (2) Bromine water — Incorrect. Bromine water brominates the activated ring of phenol, giving 2,4,6-tribromophenol; it does not replace the –OH group of an alcohol.
Option (3) Bromine in carbon disulphide — Incorrect. In this solvent of low polarity, phenol gives monobromophenols; again the bromine goes onto an aromatic ring.
Option (4) Bromine in the presence of iron(III) bromide — Incorrect. FeBr3 is the Lewis acid used for the halogenation of benzene; ethanol has no aromatic ring to brominate.
NCERT (2026-27 edition):
7.4.4 Chemical Reactions – “2. Reaction with phosphorus trihalides: Alcohols are converted to alkyl bromides by reaction with phosphorus tribromide…”