Definition: Disproportionation is a chemical reaction, typically a redox reaction, where a molecule is transformed into two or more dissimilar products.
Disproportionation reactions follow the form:
2A → A' + A"
where A, A', and A" are all different chemical species.
The reverse reaction of disproportionation is called comproportionation.
Examples: Hydrogen peroxide converting into water and oxygen is a disproportionation reaction.
2 H2O2 → H2O + O2
Water dissociating into H3O+ and OH- is an example of a disproportionation reaction that is not a redox reaction.