An aromatic primary amide A undergoes Hoffmann bromamide degradation to give an amine B . B is treated with NaNO₂ and HCl at 0-5^ C to form C . C is reacted with CuCN/KCN to form D . Complete acidic hydrolysis of D yields an aromatic carboxylic acid E which has a molar mass of 122 g mol ⁻¹ . The molar mass of the starting amide A is _______ g mol ⁻¹ .

Step-by-step solution

The aromatic carboxylic acid E has a molar mass of 122 g mol ⁻¹ . This corresponds to benzoic acid, C₆H₅COOH ( 72 + 5 + 12 + 32 + 1 = 122 g mol ⁻¹ ). Tracing the reaction sequence backwards: Complete acidic hydrolysis of a nitrile ( D ) yields a carboxylic acid. Thus, D is benzonitrile, C₆H₅CN . Reaction of a diazonium salt ( C ) with CuCN/KCN yields a nitrile. Thus, C is benzenediazonium chloride, C₆H₅N₂^+Cl^- . Diazotization of a primary aromatic amine ( B ) yields a diazonium salt. Thus, B is aniline, C₆H₅NH₂ .