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

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

In halogen chemistry:

IO₃⁻ + 5 I⁻ + 6 H ⁺ → 3 I₂ + 3 H₂O

In anammox chemistry:

NH₄⁺ + NO₂⁻ → N₂ + 2H₂O

References

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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[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.