Match List-I with List-II.
| List-I (Conversion) | List-II (Reagent) |
|---|---|
| (A) Chloroethane → Iodoethane | (I) Cuprous chloride |
| (B) Benzenediazonium chloride → Iodobenzene | (II) NaI in dry acetone |
| (C) Bromoethane → Fluoroethane | (III) Potassium iodide |
| (D) Benzenediazonium chloride → Chlorobenzene | (IV) AgF, on heating |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → A-II, B-III, C-IV, D-I
Iodo and fluoro compounds are best made by halogen exchange from an alkyl chloride or bromide. Aryl halides can be made from an arenediazonium salt, whose –N2+ group is replaced by the halogen.
(A) Chloroethane → Iodoethane — This matches (II) NaI in dry acetone (Finkelstein reaction). The NaCl formed is precipitated in dry acetone, which drives the reaction forward.
\( \displaystyle \ce{C2H5Cl + NaI} \xrightarrow{\text{dry acetone}} \ce{C2H5I + NaCl v} \)
(B) Benzenediazonium chloride → Iodobenzene — This matches (III) Potassium iodide. Replacement by iodine needs no cuprous halide; the diazonium salt is just shaken with KI.
\( \displaystyle \ce{C6H5N2^+Cl^- + KI -> C6H5I + KCl + N2 ^} \)
(C) Bromoethane → Fluoroethane — This matches (IV) AgF, on heating (Swarts reaction). Alkyl fluorides are made by heating an alkyl chloride or bromide with a metallic fluoride such as AgF, Hg2F2, CoF2 or SbF3.
\( \displaystyle \ce{C2H5Br + AgF} \xrightarrow{\Delta} \ce{C2H5F + AgBr} \)
(D) Benzenediazonium chloride → Chlorobenzene — This matches (I) Cuprous chloride (Sandmeyer’s reaction). Cuprous chloride is needed to replace the diazonium group by –Cl.
\( \displaystyle \ce{C6H5N2^+Cl^-} \xrightarrow{\ce{Cu2Cl2}} \ce{C6H5Cl + N2 ^} \)
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.” … “The synthesis of alkyl fluorides is best accomplished by heating an alkyl chloride/bromide in the presence of a metallic fluoride such as AgF, Hg2F2, CoF2 or SbF3. The reaction is termed as Swarts reaction.”
6.5 Preparation of Haloarenes – “…Mixing the solution of freshly prepared diazonium salt with cuprous chloride or cuprous bromide results in the replacement of the diazonium group by –Cl or –Br.”
“Replacement of the diazonium group by iodine does not require the presence of cuprous halide and is done simply by shaking the diazonium salt with potassium iodide.”