Dismutation

Dismutation, also known as disproportionation in many chemical contexts, is a redox reaction in which a single substance is simultaneously oxidized and reduced to yield two different species of the same element in distinct oxidation states. It is a specific form of redox where the element’s oxidation state increases in one product and decreases in another.

Key features of dismutation include the involvement of a species that can exist in at least two oxidation states and the tendency for the reaction to proceed under particular conditions, such as specific pH, temperature, or catalytic presence. The process often occurs in aqueous solution or in the gas phase and can be enhanced by catalysts or environmental factors.

Representative examples include:

- Hydrogen peroxide: 2 H2O2 → 2 H2O + O2. Here oxygen in H2O2 is −1, producing water (−2) and molecular oxygen (0).

- Nitrogen dioxide: 2 NO2 + H2O → HNO3 + HNO2, in which nitrogen shifts between +5 in nitrate and +3 in nitrite.

- Chlorine in water: Cl2 + H2O → HCl + HOCl, yielding chloride (−1) and hypochlorite (+1).

- Biological example: the dismutation of superoxide, 2 O2− + 2 H+ → H2O2 + O2, catalyzed by superoxide dismutase in many organisms.

- Hypochlorite in basic solution: 3 OCl− → ClO3− + 2 Cl−, illustrating disproportionation of hypochlorite.

Dismutation is related to comproportionation, its reverse process, where two species with different oxidation states react to form a single intermediate oxidation state of the element.