Amides are a class of organic compounds that contain the functional group –CONH₂, –CONHR, or –CONR₂. In other words, an amide consists of a carbonyl group (C=O) directly bonded to a nitrogen atom. They are considered derivatives of carboxylic acids, where the –OH group of the carboxyl group (–COOH) is replaced by an –NH₂, –NHR, or –NR₂ group.
Structure of Amides
- Primary amides: –CONH₂ (derived from ammonia)
- Secondary amides: –CONHR (derived from a primary amine)
- Tertiary amides: –CONR₂ (derived from a secondary amine)
Derivation from Carboxylic Acids
Amides are obtained by replacing the hydroxyl group (–OH) of a carboxylic acid with an amino group. However, direct reaction of carboxylic acids with ammonia or amines is not efficient, because acids and bases usually form salts instead of amides. Therefore, conversion is generally carried out in steps:
- Formation of acid derivatives
- Carboxylic acids are first converted into more reactive derivatives such as acid chlorides (R–COCl), acid anhydrides (R–CO–O–CO–R), or esters (R–COOR’).
- Reaction with ammonia or amines
- These derivatives then react with ammonia (NH₃) or amines (RNH₂, R₂NH) to form amides.
For example:
- Acid chloride + Ammonia → Primary amide
- Acid chloride + Primary amine → Secondary amide
- Acid chloride + Secondary amine → Tertiary amide
Key Points
- Amides are neutral, stable compounds with strong hydrogen bonding ability.
- They are widely found in proteins (as peptide bonds), pharmaceuticals, and synthetic polymers like nylon.