Assertion (A): Alkyl iodides are often prepared by the reaction of alkyl chlorides or bromides with NaI in dry acetone.
Reason (R): The NaCl or NaBr formed in the reaction of an alkyl chloride or bromide with NaI dissolves in dry acetone.
In the light of the above statements, choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A) is true but (R) is false.
Assertion (A): Alkyl iodides are often prepared by the reaction of alkyl chlorides or bromides with NaI in dry acetone. — True. This halogen exchange is the Finkelstein reaction:
\( \displaystyle \ce{R-X + NaI} \xrightarrow{\text{dry acetone}} \ce{R-I + NaX} \qquad (\mathrm{X = Cl,\ Br}) \)
Reason (R): The NaCl or NaBr formed in the reaction of an alkyl chloride or bromide with NaI dissolves in dry acetone. — False. NaCl and NaBr are precipitated in dry acetone.
Their removal from the solution drives the reaction forward, as Le Chatelier’s principle predicts; this is why the method gives good yields of the alkyl iodide.
NCERT (2026-27 edition):
6.4.3 Halogen Exchange – “Alkyl iodides are often prepared by the reaction of alkyl chlorides/ bromides with NaI in dry acetone. This reaction is known as Finkelstein reaction.”
“NaCl or NaBr thus formed is precipitated in dry acetone. It facilitates the forward reaction according to Le Chatelier’s Principle.”