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Comproportionation or synproportionation is a chemical reaction where two reactants, each containing the same element but with a different oxidation number, will form a product in which the elements involved reach the same oxidation number. For example, an element A in the oxidation states 0 and +2 can comproportionate 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[edit]

Main article: Frost diagram

The tendency of two species to disproportionate 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 on either side of it, then it is more stable and if in a solution, these two species will undergo comproportionation.


Pb(s) + PbO2(s) + 2 H2SO4(aq) → 2 PbSO4(s) + 2 H2O(l)
15 Se + SeCl4 + 4 AlCl3 → 2 Se8[AlCl4]2
2 H2S(g) + SO2(g) → 3 S(s) + 2 H2O(g)
IO3 + 5 I + 6 H + → 3 I2 + 3 H2O


  1. ^ [dead link]"Archived copy" (PDF). Archived from the original (PDF) on 2004-12-18. Retrieved 2005-04-13. 
  • Translated from German Wiki original