Question

Which of the following reactions is a halogenated exchange reaction:

• A. \( \text{Alkene} + HX \longrightarrow \text{Alkane with halogen} \)
• B. \( R{-}X + NaI \xrightarrow{\text{Dry acetone}} R{-}I + NaX \)
• C. \( R{-}OH + HCl \xrightarrow{\text{ZnCl}_2} R{-}Cl + H_2O \)
• D. Bromination of toluene with \( Br_2 \) and \( Fe \) in dark

Hint:

A Finkelstein reaction is a common lab method to prepare alkyl iodides by exchanging halogens using dry acetone as a solvent.

Answer 1

The Correct Option is B

Step 1: A halogen exchange reaction (also known as a halogen exchange or halogen replacement reaction) is a reaction where one halogen atom is replaced by another halogen atom.
Step 2: In option (B), an alkyl halide \( R{-}X \) reacts with sodium iodide (\( NaI \)) in dry acetone.
This results in the replacement of halogen \( X \) with iodine, forming \( R{-}I \) and sodium halide (\( NaX \)).
This is a classic halogen exchange reaction, commonly known as the Finkelstein reaction.
Step 3:
- Option (A) is an addition reaction (hydrohalogenation of alkene).
- Option (C) is a conversion of an alcohol to an alkyl halide, not an exchange of halogens.
- Option (D) is an electrophilic aromatic substitution reaction, not an exchange of halogens.