In which of the following conversions of benzenediazonium chloride is a copper salt NOT needed?

A $C X_{6} H X_{5} N X_{2} X^{+} Cl X^{-} \to C X_{6} H X_{5} I$ using $KI$
B $C X_{6} H X_{5} N X_{2} X^{+} Cl X^{-} \to C X_{6} H X_{5} CN$ using $KCN$
C $C X_{6} H X_{5} N X_{2} X^{+} Cl X^{-} \to C X_{6} H X_{5} Br$ using $HBr$
D $C X_{6} H X_{5} N X_{2} X^{+} Cl X^{-} \to C X_{6} H X_{5} Cl$ using $HCl$

Answer: A

Iodide is a good enough nucleophile and reducing agent to react with the diazonium ion directly, giving iodobenzene with no Cu catalyst. Replacement by Cl, Br or CN requires CuCl, CuBr or CuCN (Sandmeyer), or copper powder with HX (Gattermann).

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In which of the following conversions of benzenediazonium chloride is a copper salt NOT needed?

Answer: A

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