Comproportionation or synproportionation is a chemical reaction where two reactants, each containing the same element but with a different oxidation number, form a product in which the elements involved reach the same oxidation number. It is opposite to disproportionation.
The tendency of two species to disproportionate or comproportionate 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.
- In lead batteries, the spontaneous reaction is:
- Pb + PbO2 + 2 H2SO4 → 2 PbSO4 + 2 H2O
- The laboratory preparation of manganese dioxide involves comproportionation of Mn(II) and Mn(VII) reagents:
- 2 KMnO
4 + 3 MnSO
4 + 2 H
2O→ 5 MnO
2 + K
4 + 2 H
- 15 Se + SeCl4 + 4 AlCl3 → 2 Se8[AlCl4]2
- In the Claus Process, two gaseous compounds of sulfur comproportionate in the presence of a catalyst to give elemental sulfur:
- 2 H2S + SO2 → 3 S + 2 H2O
- In halogen chemistry:
- IO3− + 5 I− + 6 H + → 3 I2 + 3 H2O