Question

How can you convert aniline to benzonitrile?

Hint:

Sandmeyer reaction is excellent for introducing \(Cl\), \(Br\), or \(CN\) onto a benzene ring where direct substitution is difficult.

Answer 1

Step 1: Understanding the Concept:
Aromatic amines are typically converted to other functional groups through the versatile diazonium salt intermediates.
Step 2: Detailed Explanation:
1. Step 1 (Diazotization): Aniline is treated with nitrous acid (prepared from \(NaNO_2\) and \(HCl\)) at \(0-5^{\circ}C\). This converts the amino group into a diazonium group.
\[ C_6H_5NH_2 \xrightarrow{NaNO_2, HCl, 273-278 K} C_6H_5N_2^+Cl^- \quad (\text{Benzene diazonium chloride}) \]
2. Step 2 (Sandmeyer Reaction): The benzene diazonium chloride is then reacted with cuprous cyanide (\(CuCN\)) dissolved in aqueous potassium cyanide (\(KCN\)). The diazonium group is replaced by the nitrile group.
\[ C_6H_5N_2^+Cl^- \xrightarrow{CuCN/KCN} C_6H_5CN \quad (\text{Benzonitrile}) \]
Step 3: Final Answer:
Aniline \(\rightarrow\) Benzene diazonium chloride \(\rightarrow\) Benzonitrile.