Which of the following can be prepared from Sandmeyer's reaction?
(A) Chlorobenzene
(B) Bromobenzene
(C) Iodobenzene
(D) Fluorobenzene
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (A) and (B) only
In the Sandmeyer reaction the diazonium group of a benzenediazonium salt is replaced by Cl, Br or CN in the presence of a copper(I) salt. Iodine and fluorine are introduced by other methods.
(A) Chlorobenzene — Correct. Copper(I) chloride in HCl replaces the diazonium group by Cl.
\( \displaystyle \ce{C6H5N2^+Cl^-} \xrightarrow{\ce{CuCl/HCl}} \ce{C6H5Cl + N2} \)
(B) Bromobenzene — Correct. Copper(I) bromide in HBr gives bromobenzene in the same way.
\( \displaystyle \ce{C6H5N2^+Cl^- + HBr} \xrightarrow{\ce{CuBr}} \ce{C6H5Br + N2 + HCl} \)
(C) Iodobenzene — Incorrect. Iodine is introduced just by warming the diazonium salt with potassium iodide; no copper(I) salt is needed, so this is not a Sandmeyer reaction.
\( \displaystyle \ce{C6H5N2^+Cl^- + KI -> C6H5I + KCl + N2} \)
(D) Fluorobenzene — Incorrect. Fluorobenzene is made by treating the diazonium salt with fluoroboric acid and heating the diazonium fluoroborate formed.
\( \displaystyle \ce{C6H5N2^+Cl^- + HBF4 -> C6H5N2^+BF4^-} \xrightarrow{\Delta} \ce{C6H5F + BF3 + N2} \)
NCERT (2026-27 edition):
Replacement by Halide or Cyanide Ion
