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: Conceptual Overview:
Aromatic amines are often transformed into a variety of functional groups using diazonium salt intermediates, which play a key role in many organic reactions, including the synthesis of compounds like nitriles.
Step 2: Detailed Explanation:
1. Step 1 (Diazotization): In the first step, aniline (an aromatic amine) is treated with nitrous acid, which is generated by reacting sodium nitrite (\( NaNO_2 \)) with hydrochloric acid (\( HCl \)) at a low temperature of \( 0-5^{\circ}C \). This reaction converts the amino group (\( -NH_2 \)) into a diazonium group (\( -N_2^+ \)). The reaction is as follows: \[ C_6H_5NH_2 \xrightarrow{NaNO_2, HCl, 273-278 K} C_6H_5N_2^+Cl^- \quad (\text{Benzene diazonium chloride}) \] 2. Step 2 (Sandmeyer Reaction): In the second step, the benzene diazonium chloride formed in the previous step reacts with cuprous cyanide (\( CuCN \)) dissolved in aqueous potassium cyanide (\( KCN \)). This substitution reaction replaces the diazonium group with a nitrile group, yielding benzonitrile. The reaction is: \[ C_6H_5N_2^+Cl^- \xrightarrow{CuCN/KCN} C_6H_5CN \quad (\text{Benzonitrile}) \] Step 3: Final Conclusion:
The overall reaction involves the conversion of aniline to benzene diazonium chloride, followed by substitution to form benzonitrile: Aniline \( \rightarrow \) Benzene diazonium chloride \( \rightarrow \) Benzonitrile.