Which of the following compounds can be prepared by Sandmeyer's reaction?
(A) Chlorobenzene
(B) Bromobenzene
(C) Cyanobenzene
(D) Fluorobenzene
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A), (B) and (C) only
In the Sandmeyer reaction the diazonium group of benzene diazonium chloride is replaced by Cl, Br or CN, using the corresponding copper(I) salt; nitrogen gas is released. Fluorine and iodine cannot be introduced this way.
(A) Chlorobenzene — Correct.
\( \displaystyle \ce{C6H5N2+Cl^-} \xrightarrow{\ce{CuCl}/\ce{HCl}} \ce{C6H5Cl + N2} \)
(B) Bromobenzene — Correct.
\( \displaystyle \ce{C6H5N2^+Cl^- + HBr} \xrightarrow{\ce{CuBr}} \ce{C6H5Br + N2 + HCl} \)
(C) Cyanobenzene — Correct.
\( \displaystyle \ce{C6H5N2^+Cl^- + KCN} \xrightarrow{\ce{CuCN}} \ce{C6H5CN + N2 + KCl} \)
(D) Fluorobenzene — Incorrect. Fluorobenzene is made by the Balz–Schiemann reaction: the diazonium salt is treated with fluoroboric acid, and the precipitated diazonium fluoroborate is heated.
\( \displaystyle \ce{C6H5N2+Cl^- + HBF4 -> C6H5N2+BF4^- + HCl} \)
\( \displaystyle \ce{C6H5N2+BF4^-} \xrightarrow{\text{heat}} \ce{C6H5F + BF3 + N2} \)
NCERT (2026-27 edition):
Replacement by Halide or Cyanide Ion
