How will you obtain the following from benzenediazonium chloride? Give chemical equations involved:
\[
(a)\;\text{Chlorobenzene}
\]
\[
(b)\;\text{Benzene}
\]
\[
(c)\;\text{Benzonitrile}
\]
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Solution and Explanation
Benzenediazonium chloride is an important intermediate in aromatic substitution. The diazonium group \((-N_2^+Cl^-)\) can be replaced by several groups. Loss of nitrogen gas makes these reactions favourable.
Step 1: Preparation of chlorobenzene.
Benzenediazonium chloride reacts with cuprous chloride and hydrochloric acid. This is Sandmeyer reaction. \[ C_6H_5N_2^+Cl^-+CuCl \rightarrow C_6H_5Cl+N_2+Cu^+ \] Hence: \[ \boxed{C_6H_5Cl} \]
Step 2: Preparation of benzene.
Benzenediazonium chloride is reduced by hypophosphorous acid. \[ C_6H_5N_2^+Cl^-+H_3PO_2+H_2O \rightarrow C_6H_6+N_2+H_3PO_3+HCl \] Hence: \[ \boxed{C_6H_6} \]
Step 3: Preparation of benzonitrile.
Benzenediazonium chloride reacts with cuprous cyanide in presence of potassium cyanide. \[ C_6H_5N_2^+Cl^- \xrightarrow{CuCN/KCN} C_6H_5CN+N_2+Cl^- \] Hence: \[ \boxed{C_6H_5CN} \] Hence: \[ \boxed{C_6H_5N_2^+Cl^-\xrightarrow{CuCl/HCl}C_6H_5Cl+N_2} \] \[ \boxed{C_6H_5N_2^+Cl^-\xrightarrow{H_3PO_2}C_6H_6+N_2} \] \[ \boxed{C_6H_5N_2^+Cl^-\xrightarrow{CuCN/KCN}C_6H_5CN+N_2} \]
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