Оксидтану-тотығу аралық күйіндегі қосылыстардың өзгеруі

Redox reaction whose products have higher and lower oxidation states than the reactant

In chemistry, disproportionation, sometimes called dismutation, is a redox reaction in which one compound of intermediate oxidation state converts to two compounds, one of higher and one of lower oxidation states. The reverse of disproportionation, such as when a compound in an intermediate oxidation state is formed from precursors of lower and higher oxidation states, is called comproportionation, also known as synproportionation. More generally, the term can be applied to any desymmetrizing reaction where two molecules of one type react to give one each of two different types:
2A > A' + A''
This expanded definition is not limited to redox reactions, but also includes some molecular autoionization reactions, such as the self ionization of water. In contrast, some authors use the term redistribution to refer to reactions of this type (in either direction) when only ligand exchange but no redox is involved and distinguish such processes from disproportionation and comproportionation. For example, the Schlenk equilibrium

2 RMgX > R2Mg + MgX2

is an example of a redistribution reaction.

Sulfur isotopes of sediments are often measured for studying environments in the Earth's past (Paleoenvironment). Disproportionation of sulfur intermediates, being one of the processes affecting sulfur isotopes of sediments, has drawn attention from geoscientists for studying the redox conditions in the oceans in the past. Sulfate reducing bacteria fractionate sulfur isotopes as they take in sulfate and produce sulfide. Prior to 2010s, it was thought that sulfate reduction could fractionate sulfur isotopes up to 46 permil and fractionation larger than 46 permil recorded in sediments must be due to disproportionation of sulfur intermediates in the sediment. This view has changed since the 2010s. As substrates for disproportionation are limited by the product of sulfate reduction, the isotopic effect of disproportionation should be less than 16 permil in most sedimentary settings. Disproportionation can be carried out by microorganisms obligated to disproportionation or microorganisms that can carry out sulfate reduction as well. Common substrates for disproportionation include elemental sulfur, thiosulfate and sulfite.