Nucleophilic Properties of Amines
Quick Notes
- Amines can act as nucleophiles due to the lone pair of electrons on the nitrogen atom, which can attack electron-deficient species.
- Nucleophiles are electron pair donors.
- Amines undergo nucleophilic substitution with halogenoalkanes to form:
- Primary, secondary, tertiary amines and quaternary ammonium salts.
- Quaternary ammonium salts are used as cationic surfactants in detergents and fabric softeners.
- Amines also undergo nucleophilic addition–elimination reactions with acyl chlorides and acid anhydrides to form amides.
Full Notes
Nucleophilic Substitution with Halogenoalkanes
Amines undergo nucleophilic substitution with halogenoalkanes to form primary, secondary, tertiary amines and quaternary ammonium salts.
The lone pair of electrons on the Nitrogen atom enable them to act as nucleophiles (electron pair donors).
The reactions follow a nucleophilic substitution mechanism:
(see Halogenoalkanes for more detail)
Uses of Quaternary Ammonium Salts
Quaternary ammonium salts (R4N+X−) are used as cationic surfactants.
Applications:
Fabric softeners
Hair conditioners
Detergents
How They Work:
- Hydrophobic (non-polar carbon alkyl group) tail interacts with grease.
- Hydrophilic head (polar and charged R4N+ group) interacts with water.
- Helps remove oils and dirt during cleaning.
Nucleophilic Addition–Elimination with Acyl Chlorides and Acid Anhydrides
Amines react with acyl chlorides and acid anhydrides to form amides.
Mechanism: Nucleophilic addition–elimination.
Reagents: Acyl chloride (RCOCl) + Ammonia/Primary Amine.
ExampleReaction (Primary Amine with acyl chloride — example of ethanoyl chloride + ethylamine):
Amines react similarly with acid anhydrides, however carboxylic acids are also formed.
Summary
- Amines act as nucleophiles because the nitrogen lone pair can be donated to electron-deficient centres.
- With halogenoalkanes, amines undergo nucleophilic substitution to give primary, secondary, tertiary amines and quaternary ammonium salts.
- Quaternary ammonium salts (R4N+X−) function as cationic surfactants in detergents, fabric softeners and hair conditioners.
- Amines react with acyl chlorides and acid anhydrides via nucleophilic addition–elimination to form amides; acid anhydrides additionally produce a carboxylic acid.