Comproportionation

Symproportionation or comproportionation is a chemical reaction where two reactants, each containing the same element but with a different oxidation number, will form a product with an oxidation number intermediate of the two reactants. For example, an element A in the oxidation states 0 and +2 can symproportionate to the state +1. It is opposite to disproportionation, where two or more atoms of the same element originally having the same oxidation state react with other chemical(s) or themselves to give different oxidation numbers.

Frost diagrams

Main article: Frost diagram

The tendency of two species to symproportionate can be determined by examining the Frost diagram of the oxidation states; if a species' value of ΔG/F is lower than the line joining the two oxidation numbers either side of it, then it is more stable than a solution of these two species and they will undergo symproportionation.

Examples of symproportionation

• In lead batteries, the spontaneous reaction is:

Pb(s) + PbO₂(s) + 2 H₂SO₄(aq) → 2 PbSO₄(s) + 2 H₂O(l)

• Potassium permanganate contains manganese with oxidation number of +7 and reacts with a manganese compound having oxidation number +2 to yield Manganese(IV) oxide (manganese dioxide) with oxidation number +4, potassium hydroxide and water.
• In chalcogen chemistry:

15 Se + SeCl₄ + 4 AlCl₃ → 2 Se₈[AlCl₄]₂ ^[1]

• In volcanic eruptions, a redox reaction involving sulfur compounds occurs:

2 H₂S(g) + SO₂(g) → 3 S(s) + 2 H₂O(g)

• In halogen chemistry:

IO₃^- + 5 I^- + 6 H ⁺ → 3 I₂ + 3 H₂O

References

1. ^ [1]

• Translated from German Wiki original