Amines react with acids in a straightforward acid-base reaction because amines are basic (they can donate their lone pair on nitrogen to accept a proton). Here’s a clear explanation:
General Reaction
- The nitrogen atom in an amine has a lone pair of electrons.
- When an amine reacts with an acid (like hydrochloric acid, sulfuric acid, or nitric acid), it accepts a proton (H⁺) from the acid.
- This forms an ammonium salt, which is ionic and usually solid or soluble in water.
Example of the Reaction
- A simple primary, secondary, or tertiary amine reacts with hydrochloric acid to form a corresponding ammonium chloride.
- The reaction is reversible in solution but produces a stable salt that can be isolated as a solid.
Key Points
- Primary, secondary, and tertiary amines all form salts with acids.
- The reaction increases the solubility of amines in water because the ammonium salts are ionic.
- This property is widely used in purifying amines: an amine can be converted into its salt, filtered, and then regenerated as a free amine by adding a base.
Summary
- Amines act as bases.
- With acids, they form ammonium salts.
- This reaction is useful for purification and handling amines, since many free amines are volatile or malodorous, but the salts are solid and easier to manage.