Which of the following statements is correct for benzene diazonium sa…

The correct answer is Option (2) → (C) and (D) only

Benzenediazonium salts (\( \ce{C6H5N2^{+}X^{-}} \)) are made from aniline with \( \ce{NaNO2} \) and HCl at 273–278 K. They are useful because the –\( \ce{N2^{+}} \) group is an excellent leaving group (\( \ce{N2} \) gas escapes) and can be replaced by many groups; they also keep the nitrogen in coupling reactions.

• (A) Diazonium salt does not decompose easily. — Incorrect. Benzenediazonium chloride is stable only in the cold; it reacts with water on warming and decomposes easily in the dry state, so it is used at once. (Only the fluoroborate is stable at room temperature.)

• (B) In Gattermann reaction diazonium group is replaced by chlorine using Cu(I) ion and HCl. — Incorrect. The Gattermann reaction uses copper powder with HCl. Using Cu(I) (\( \ce{Cu2Cl2} \)) with HCl is the Sandmeyer reaction.

      \( \displaystyle \ce{C6H5N2^+Cl^-} \xrightarrow{\ce{Cu}/\ce{HCl}} \ce{C6H5Cl + N2} \)

• (C) When Diazonium fluoroborate is heated with aqueous sodium nitrite solution in the presence of copper, the diazonium group is replaced by -\( \ce{NO2} \). — Correct. This gives nitrobenzene.

      \( \displaystyle \ce{C6H5N2^+BF4^-} \xrightarrow{\ce{NaNO2}/\ce{Cu},\ \text{heat}} \ce{C6H5NO2 + N2} \)

• (D) Azo dye is formed via coupling reaction of benzene diazonium salt. — Correct. With phenol, the diazonium ion couples at the para position to give the orange dye p-hydroxyazobenzene (–N=N– kept).

      \( \displaystyle \ce{C6H5N2^+Cl^- + C6H5OH} \xrightarrow{\ce{OH^-}} \ce{C6H5-N=N-C6H4-OH + HCl} \)