Amines as Bases

Amines, like ammonia, are Brønsted-Lowry bases: they are proton acceptors. The lone pair on the nitrogen atom forms a dative covalent bond to an H⁺ ion.In water. An amine takes a proton from a water molecule, forming an alkylammonium ion and hydroxide ions, so solutions of amines are alkaline:CH₃NH₂ + H₂O ⇌ CH₃NH₃⁺ + OH⁻The equilibrium lies well to the left: only a small fraction of the amine reacts, so amines are weak bases.With acids. Amines are neutralised by acids to form salts. The nitrogen accepts the proton and the anion from the acid becomes the counter-ion:CH₃NH₂ + HCl → CH₃NH₃⁺Cl⁻The product is methylammonium chloride. The salts are named like ammonium salts: the amine name ending -amine becomes -ammonium. Ethylamine and hydrochloric acid give ethylammonium chloride; with sulfuric acid, two amine molecules react with each H₂SO₄.These salts are ionic, white crystalline solids that dissolve well in water and have no fishy smell. This is used to make amine-based drugs more soluble.Getting the amine back. Adding a strong base such as NaOH(aq) removes the proton again and releases the free amine:CH₃NH₃⁺Cl⁻ + NaOH → CH₃NH₂ + NaCl + H₂O