Autoprotolysis

In autoprotolysis 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.

2H
₂O ⇌ OH⁻
+ H
₃O⁺

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:

2NH
₃ ⇌ NH⁻
₂ + NH⁺
₄

Another example is acetic acid:

2CH
₃COOH ⇌ CH
₃COO⁻
+ CH
₃COOH⁺
₂