Autoprotolysis

In chemistry, autoprotolysis is a chemical reaction in which a proton is transferred between two identical molecules, one of which acts as a Brønsted acid, releasing a proton which is accepted by the other molecule acting as a Brønsted base. For example, water undergoes autoprotolysis in the self-ionization of water reaction. It is a type of molecular autoionization.

2 H₂O ⇌ OH⁻ + H₃O⁺

Any solvent that contains both acidic hydrogen and lone pairs of electrons to accept H⁺ can undergo autoprotolysis. For example, ammonia in its purest form may undergo autoprotolysis:

2 NH₃ ⇌ NH−2 + NH+4

Another example is acetic acid:

2 CH₃COOH ⇌ CH₃COO⁻ + CH₃COOH+2