Amides

An amide contains the –CONH– group. A primary amide is –CONH₂ (e.g. ethanamide, CH₃CONH₂); an N-substituted amide has a group on the nitrogen (e.g. N-methylethanamide, CH₃CONHCH₃).

Amides are made by reacting an acyl chloride with ammonia or an amine: $\text{CH}_3\text{COCl} + \text{NH}_3 \rightarrow \text{CH}_3\text{CONH}_2 + \text{HCl}$ $\text{CH}_3\text{COCl} + \text{CH}_3\text{NH}_2 \rightarrow \text{CH}_3\text{CONHCH}_3 + \text{HCl}$

This is the standard route to the amide (and, between amino acids, the peptide) bond.

Amides are hydrolysed (slowly, on refluxing) in two ways:

• Acid hydrolysis (dilute acid) → carboxylic acid + ammonium salt: $\text{CH}_3\text{CONH}_2 + \text{H}_2\text{O} + \text{HCl} \rightarrow \text{CH}_3\text{COOH} + \text{NH}_4\text{Cl}$
• Alkaline hydrolysis (dilute NaOH) → carboxylate salt + ammonia: $\text{CH}_3\text{CONH}_2 + \text{NaOH} \rightarrow \text{CH}_3\text{COONa} + \text{NH}_3$

(The released NH₃ can be detected with damp red litmus, which turns blue.) This pattern — acid gives the acid + an ammonium salt, alkali gives the salt + free ammonia — mirrors the hydrolysis of nitriles.

Both amines and amides contain nitrogen, yet amines are basic while amides are essentially neutral. The difference is the availability of the nitrogen lone pair.

• In an amine, the N lone pair is available to accept a proton → basic.
• In an amide, the nitrogen is next to a C=O group, and its lone pair is delocalised onto the carbonyl oxygen (into the C=O system). With the lone pair tied up, it is not available to accept a proton → the amide is essentially neutral.

This is the same kind of lone-pair-delocalisation argument that explains why phenylamine is a weak base.