Comproportionation

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.[1]

Frost diagrams
Main article: Frost diagram

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.

Examples
  • 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
2SO
4 + 2 H
2SO
4
  • 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
IO3− + 5 I− + 6 H + → 3 I2 + 3 H2O
NH4+ + NO2− → N2 + 2H2O


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References
  1. Shriver, D. F.; Atkins, P. W.; Overton, T. L.; Rourke, J. P.; Weller, M. T.; Armstrong, F. A. “Inorganic Chemistry” W. H. Freeman, New York, 2006. ISBN 0-7167-4878-9.
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