Disproportionation
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In
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:[3]
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
is an example of a redistribution reaction.
History
The first disproportionation reaction to be studied in detail was:
This was examined using tartrates by Johan Gadolin in 1788. In the Swedish version of his paper he called it söndring.[4][5]
Examples
- Mercury(I) chloride disproportionates upon UV-irradiation:[clarification needed]
- Phosphorous acid disproportionates upon heating to give phosphoric acid and phosphine:[clarification needed]
- Desymmetrizing reactions are sometimes referred to as disproportionation, as illustrated by the thermal degradation of bicarbonate:
- The oxidation numbers remain constant in this acid-base reaction.
- Another variant on disproportionation is radical disproportionation, in which two radicals form an alkene and an alkane.
- Disproportionation of sulfur intermediates by microorganisms are widely observed in sediments.[6][7][8][9]
- Chlorine gas reacts with dilute sodium hydroxide to form sodium chloride, sodium chlorate and water. The ionic equation for this reaction is as follows:[10]
- The chlorine reactant is in oxidation state 0. In the products, the chlorine in the Cl− ion has an oxidation number of −1, having been reduced, whereas the oxidation number of the chlorine in the ClO3− ion is +5, indicating that it has been oxidized.
- Decomposition of numerous interhalogen compounds involve disproportionation. Bromine fluoride undergoes disproportionation reaction to form bromine trifluoride and bromine in non-aqueous media:[11][citation needed]
- The dismutation of free radical to hydrogen peroxide and oxygen, catalysed in living systems by the enzyme superoxide dismutase:
- The oxidation state of oxygen is −1/2 in the superoxide free radical anion, −1 in hydrogen peroxide and 0 in dioxygen.
- In the Cannizzaro reaction, an aldehyde is converted into an alcohol and a carboxylic acid. In the related Tishchenko reaction, the organic redox reaction product is the corresponding ester. In the Kornblum–DeLaMare rearrangement, a peroxide is converted to a ketone and an alcohol.
- The disproportionation of hydrogen peroxide into water and oxygen catalysed by either potassium iodide or the enzyme catalase:
- In the carbon nanotubes, high-pressure carbon monoxidedisproportionates when catalysed on the surface of an iron particle:
- Nitrogen has oxidation state +4 in nitrogen dioxide, but when this compound reacts with water, it forms both nitric acid and nitrous acid, where nitrogen has oxidation states +5 and +3 respectively:
- Dithionite undergoes acid hydrolysis to thiosulfate and bisulfite:[12]
- Dithionate is prepared on a larger scale by oxidizing a cooled aqueous solution of sulfur dioxide with manganese dioxide:[13][citation needed]
Polymer chemistry
In free-radical chain-growth polymerization, chain termination can occur by a disproportionation step in which a hydrogen atom is transferred from one growing chain molecule to another one, which produces two dead (non-growing) chains.[14]
- Chain—CH2–CHX• + Chain—CH2–CHX• → Chain—CH=CHX + Chain—CH2–CH2X
in which, Chain— represents the already formed polymer chain, and • indicates a reactive free radical.
Biochemistry
In 1937,
The dismutation of pyruvic acid in other small organic molecules (ethanol + CO2, or lactate and acetate, depending on the environmental conditions) is also an important step in
Another example of biochemical dismutation reaction is the disproportionation of acetaldehyde into ethanol and acetic acid.[16]
While in
Disproportionation of sulfur intermediates
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[18] 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.[19] 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.[9]
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.[9]
Claus reaction: a comproportionation reaction
The
The Claus reaction is one of the chemical reactions involved in the Claus process used for the desulfurization of gases in the oil refinery plants and leading to the formation of solid elemental sulfur, more easy to store, transport and dispose off.
See also
- Dismutase
- Oxidoreductase
- Fermentation (biochemistry)
References
- ISBN 0-7167-4878-9.
- ISBN 0-12-352651-5.
- ^ Gadolin Johan (1788) K. Sv. Vet. Acad. Handl. 1788, 186-197.
- ^ Gadolin Johan (1790) Crells Chem. Annalen 1790, I, 260-273.
- PMC 202062.
- ISSN 0016-7037.
- ISSN 0016-7037.
- ^ ISSN 0009-2541.
- ISBN 0-85404-690-9
- ^ Book: Non-Aqueous Media, exact reference of this book is lacking: need to be completed!.
- ^ ISBN 978-3527306732.
- ^ J. Meyer and W. Schramm, Z. Anorg. Chem., 132 (1923) 226. Cited in: A Comprehensive Treatise on Theoretical and Inorganic Chemistry, by J.W. Meller, John Wiley and Sons, New York, Vol. XII, p. 225.
- ISBN 0-216-92980-6.
- PMID 16746383.
- ^ Biochemical basis of mitochondrial acetaldehyde dismutation in Saccharomyces cerevisiae
- S2CID 27142031.
- ISSN 0304-4203.
- ISSN 0036-8075.