Amides — common mistakes

A very common exam question involves identifying the products of hydrolysis. Remember the rule: in acid, the amine product is a salt (RNH₃⁺); in alkali, the acid product is a salt (RCOO⁻). Always check the pH of the final mixture to determine the form of the products.

The key difference lies in the availability of the lone pair of electrons on the nitrogen atom. In an amine (like R-NH₂), this lone pair is localised on the nitrogen and is readily available to accept a proton (H⁺), making amines basic. In an amide (R-CONH₂), the nitrogen is adjacent to a carbonyl group (C=O). The electron-withdrawing nature of the carbonyl group and resonance effects mean the nitrogen's lone pair is delocalised into the C=O pi system. This makes the lone pair unavailable to accept a proton, so amides are neutral.

The initial products are the same (a carboxylic acid and an amine/ammonia), but they immediately react with the excess acid or alkali. In acid hydrolysis, the amine/ammonia product is basic, so it gets protonated to form an ammonium salt (e.g., NH₄⁺ or RNH₃⁺). The carboxylic acid remains as RCOOH. In alkaline hydrolysis, the carboxylic acid product is acidic, so it gets deprotonated to form a carboxylate salt (e.g., RCOO⁻Na⁺). The amine/ammonia remains as a free base (NH₃ or RNH₂).