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.
2O ⇌ OH−
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:
3 ⇌ NH−
2 + NH+
Another example is acetic acid:
3COOH ⇌ CH