Disproportionation

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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 state. [1] [2] 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 symproportionation.

Contents

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]

2 A → 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.

History

The first disproportionation reaction to be studied in detail was:

2 Sn2+ → Sn4+ + Sn

This was examined using tartrates by Johan Gadolin in 1788. In the Swedish version of his paper he called it söndring. [4] [5]

Examples

Hg2Cl2 → HgCl2 + Hg
4 H3PO3 → 3 H3PO4 + PH3
2 HCO−3 → CO2−3 + H2CO3
The oxidation numbers remain constant in this acid-base reaction.
4 S0 + 4 H2O → 3 H2S + SO2−4 + 2 H+
3 S0 + 2 FeOOH → SO2−4 + 2 FeS + 2 H+
4 SO2−3 + 2 H+ → H2S + SO2−4
3 Cl2 + 6 OH− → 5 Cl− + ClO−3 + 3 H2O
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 ClO−3 ion is +5, indicating that it has been oxidized.
3 BrF → BrF3 + Br2
2 O−2 + 2 H+ → H2O2 + O2
The oxidation state of oxygen is −1⁄2 in the superoxide free radical anion, −1 in hydrogen peroxide and 0 in dioxygen.
2 H2O2 → 2 H2O + O2
2 CO → C + CO2
2 NO2 + H2O → HNO3 + HNO2
Under acidic conditions, hydrazoic acid disproportionates as:
3 HN3 + H+ → 4 N2 + NH+4
Under neutral, or basic, conditions, the azide anion disproportionates as:
3 N−3 + 3 H2O → 4 N2 + NH3 + 3 OH−
2 S2O2−4 + H2O → S2O2−3 + 2 HSO−3
3 Na2S2O4 + 6 NaOH → 5 Na2SO3 + Na2S + 3 H2O
2 MnO2 + 3 SO2 → MnS2O6 + MnSO4

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. [15]

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, Hans Adolf Krebs, who discovered the citric acid cycle bearing his name, confirmed the anaerobic dismutation of pyruvic acid into lactic acid, acetic acid and CO2 by certain bacteria according to the global reaction: [16]

2 CH3COCOOH + H2O → CH3CH(OH)COOH + CH3COOH + CO2

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 fermentation reactions. Fermentation reactions can also be considered as disproportionation or dismutation biochemical reactions. Indeed, the donor and acceptor of electrons in the redox reactions supplying the chemical energy in these complex biochemical systems are the same organic molecules simultaneously acting as reductant or oxidant.

Another example of biochemical dismutation reaction is the disproportionation of acetaldehyde into ethanol and acetic acid. [17]

While in respiration electrons are transferred from substrate (electron donor) to an electron acceptor, in fermentation part of the substrate molecule itself accepts the electrons. Fermentation is therefore a type of disproportionation, and does not involve an overall change in oxidation state of the substrate. Most of the fermentative substrates are organic molecules. However, a rare type of fermentation may also involve the disproportionation of inorganic sulfur compounds in certain sulfate-reducing bacteria. [18]

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 ‰ [19] and fractionation larger than 46 ‰ recorded in sediments must be due to disproportionation of sulfur intermediates in the sediment. This view has changed since the 2010s. [20] As substrates for disproportionation are limited by the product of sulfate reduction, the isotopic effect of disproportionation should be less than 16 ‰ 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 (S8), thiosulfate (S2O2−3) and sulfite (SO2−3). [9]

Claus reaction: a comproportionation reaction

The Claus reaction is an example of comproportionation reaction (the inverse of disproportionation) involving hydrogen sulfide (H2S) and sulfur dioxide (SO2) to produce elemental sulfur and water as follows:

2 H2S + SO2 → 3 S + 2 H2O

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 (S8), which is easier to store, transport, reuse when possible, and dispose of.

See also

Related Research Articles

<span class="mw-page-title-main">Sulfur</span> Chemical element with atomic number 16 (S)

Sulfur (also spelled sulphur in British English) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with the chemical formula S8. Elemental sulfur is a bright yellow, crystalline solid at room temperature.

Sulfide (also sulphide in British English ) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. Sulfide also refers to large families of inorganic and organic compounds, e.g. lead sulfide and dimethyl sulfide. Hydrogen sulfide (H2S) and bisulfide (SH−) are the conjugate acids of sulfide.

<span class="mw-page-title-main">Cerium(IV) sulfate</span> Chemical compound

Cerium(IV) sulfate, also called ceric sulfate, is an inorganic compound. It exists as the anhydrous salt Ce(SO4)2 as well as a few hydrated forms: Ce(SO4)2(H2O)x, with x equal to 4, 8, or 12. These salts are yellow to yellow/orange solids that are moderately soluble in water and dilute acids. Its neutral solutions slowly decompose, depositing the light yellow oxide CeO2. Solutions of ceric sulfate have a strong yellow color. The tetrahydrate loses water when heated to 180-200 °C.

Comproportionation or symproportionation is a chemical reaction where two reactants containing the same element but with different oxidation numbers, form a compound having an intermediate oxidation number. It is the opposite of disproportionation.

In horticulture, lime sulfur (lime sulphur in British English, see American and British English spelling differences) is mainly a mixture of calcium polysulfides and thiosulfate (plus other reaction by-products as sulfite and sulfate) formed by reacting calcium hydroxide with elemental sulfur, used in pest control. It can be prepared by boiling in water a suspension of poorly soluble calcium hydroxide (lime) and solid sulfur together with a small amount of surfactant to facilitate the dispersion of these solids in water. After elimination of residual solids (flocculation, decantation, and filtration), it is normally used as an aqueous solution, which is reddish-yellow in colour and has a distinctive offensive odor of hydrogen sulfide (H2S, rotten eggs).

<span class="mw-page-title-main">Sulfur cycle</span> Biogeochemical cycle of sulfur

The important sulfur cycle is a biogeochemical cycle in which the sulfur moves between rocks, waterways and living systems. It is important in geology as it affects many minerals and in life because sulfur is an essential element (CHNOPS), being a constituent of many proteins and cofactors, and sulfur compounds can be used as oxidants or reductants in microbial respiration. The global sulfur cycle involves the transformations of sulfur species through different oxidation states, which play an important role in both geological and biological processes. Steps of the sulfur cycle are:

<span class="mw-page-title-main">Sodium dithionite</span> Chemical compound

Sodium dithionite is a white crystalline powder with a sulfurous odor. Although it is stable in dry air, it decomposes in hot water and in acid solutions.

<span class="mw-page-title-main">Sodium dithionate</span> Chemical compound

Sodium dithionate Na2S2O6 is an important compound for inorganic chemistry. It is also known under names disodium dithionate, sodium hyposulfate, and sodium metabisulfate. The sulfur can be considered to be in its +5 oxidation state.

<span class="mw-page-title-main">Sulfur-reducing bacteria</span> Microorganisms able to reduce elemental sulfur to hydrogen sulfide

Sulfur-reducing bacteria are microorganisms able to reduce elemental sulfur (S0) to hydrogen sulfide (H2S). These microbes use inorganic sulfur compounds as electron acceptors to sustain several activities such as respiration, conserving energy and growth, in absence of oxygen. The final product of these processes, sulfide, has a considerable influence on the chemistry of the environment and, in addition, is used as electron donor for a large variety of microbial metabolisms. Several types of bacteria and many non-methanogenic archaea can reduce sulfur. Microbial sulfur reduction was already shown in early studies, which highlighted the first proof of S0 reduction in a vibrioid bacterium from mud, with sulfur as electron acceptor and H
2 as electron donor. The first pure cultured species of sulfur-reducing bacteria, Desulfuromonas acetoxidans, was discovered in 1976 and described by Pfennig Norbert and Biebel Hanno as an anaerobic sulfur-reducing and acetate-oxidizing bacterium, not able to reduce sulfate. Only few taxa are true sulfur-reducing bacteria, using sulfur reduction as the only or main catabolic reaction. Normally, they couple this reaction with the oxidation of acetate, succinate or other organic compounds. In general, sulfate-reducing bacteria are able to use both sulfate and elemental sulfur as electron acceptors. Thanks to its abundancy and thermodynamic stability, sulfate is the most studied electron acceptor for anaerobic respiration that involves sulfur compounds. Elemental sulfur, however, is very abundant and important, especially in deep-sea hydrothermal vents, hot springs and other extreme environments, making its isolation more difficult. Some bacteria – such as Proteus, Campylobacter, Pseudomonas and Salmonella – have the ability to reduce sulfur, but can also use oxygen and other terminal electron acceptors.

<span class="mw-page-title-main">Dithionite</span> Oxyanion of sulfur at the oxidation number +3

The dithionite is the oxyanion with the formula [S2O4]2−. It is commonly encountered as the salt sodium dithionite. For historical reasons, it is sometimes called hydrosulfite, but it contains no hydrogen and is not a sulfite. The dianion has a steric number of 4 and trigonal pyramidal geometry.

<span class="mw-page-title-main">Thiosulfate</span> Polyatomic ion (S2O3, charge –2)

Thiosulfate is an oxyanion of sulfur with the chemical formula S2O2−3. Thiosulfate also refers to the compounds containing this anion, which are the salts of thiosulfuric acid, such as sodium thiosulfate Na2S2O3 and ammonium thiosulfate (NH4)2S2O3. Thiosulfate salts occur naturally. Thiosulfate rapidly dechlorinates water, and is used to halt bleaching in the paper-making industry. Thiosulfate salts are mainly used for dyeing in textiles, and bleaching of natural substances.

Microbial metabolism is the means by which a microbe obtains the energy and nutrients it needs to live and reproduce. Microbes use many different types of metabolic strategies and species can often be differentiated from each other based on metabolic characteristics. The specific metabolic properties of a microbe are the major factors in determining that microbe's ecological niche, and often allow for that microbe to be useful in industrial processes or responsible for biogeochemical cycles.

A polysulfane is a chemical compound of formula H2Sn, where n > 1. Compounds containing 2 – 8 sulfur atoms have been isolated, longer chain compounds have been detected, but only in solution. H2S2 is colourless, higher members are yellow with the colour increasing with the sulfur content. In the chemical literature the term polysulfanes is sometimes used for compounds containing −(S)n−, e.g. organic polysulfanes R1−(S)n−R2.

Sulfur is metabolized by all organisms, from bacteria and archaea to plants and animals. Sulfur can have an oxidation state from -2 to +6 and is reduced or oxidized by a diverse range of organisms. The element is present in proteins, sulfate esters of polysaccharides, steroids, phenols, and sulfur-containing coenzymes.

<span class="mw-page-title-main">Ammonium sulfite</span> Chemical compound

Ammonium sulfite is the ammonium salt of sulfurous acid with the chemical formula (NH4)2SO3.

<span class="mw-page-title-main">Sulfoxylic acid</span> Chemical compound

Sulfoxylic acid (H2SO2) (also known as hyposulfurous acid or sulfur dihydroxide) is an unstable oxoacid of sulfur in an intermediate oxidation state between hydrogen sulfide and dithionous acid. It consists of two hydroxy groups attached to a sulfur atom. Sulfoxylic acid contains sulfur in an oxidation state of +2. Sulfur monoxide (SO) can be considered as a theoretical anhydride for sulfoxylic acid, but it is not actually known to react with water.

<span class="mw-page-title-main">Microbial oxidation of sulfur</span>

Microbial oxidation of sulfur is the oxidation of sulfur by microorganisms to build their structural components. The oxidation of inorganic compounds is the strategy primarily used by chemolithotrophic microorganisms to obtain energy to survive, grow and reproduce. Some inorganic forms of reduced sulfur, mainly sulfide (H2S/HS−) and elemental sulfur (S0), can be oxidized by chemolithotrophic sulfur-oxidizing prokaryotes, usually coupled to the reduction of oxygen (O2) or nitrate (NO3−). Anaerobic sulfur oxidizers include photolithoautotrophs that obtain their energy from sunlight, hydrogen from sulfide, and carbon from carbon dioxide (CO2).

Gold(III) sulfide or auric sulfide is an inorganic compound with the formula Au2S3. Auric sulfide has been described as a black and amorphous solid. Only the amorphous phase has been produced, and the only evidence of existence is based on thermal analysis.

Sulfur isotope biogeochemistry is the study of the distribution of sulfur isotopes in biological and geological materials. In addition to its common isotope, 32S, sulfur has three rare stable isotopes: 34S, 36S, and 33S. The distribution of these isotopes in the environment is controlled by many biochemical and physical processes, including biological metabolisms, mineral formation processes, and atmospheric chemistry. Measuring the abundance of sulfur stable isotopes in natural materials, like bacterial cultures, minerals, or seawater, can reveal information about these processes both in the modern environment and over Earth history.

<span class="mw-page-title-main">Potassium thiosulfate</span> Chemical compound

'Potassium thiosulfate is an inorganic compound with the formula K2S2O3. This salt can form multiple hydrates, such as the monohydrate, dihydrate, and the pentahydrate, all of which are white or colorless solids. It is used as a fertilizer.

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.
  2. ↑ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN   0-12-352651-5.
  3. ↑ IUPAC , Compendium of Chemical Terminology , 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) " disproportionation ". doi : 10.1351/goldbook.D01799
  4. ↑ Gadolin Johan (1788) K. Sv. Vet. Acad. Handl. 1788, 186-197.
  5. ↑ Gadolin Johan (1790) Crells Chem. Annalen 1790, I, 260-273.
  6. ↑ Thamdrup, Bo; Finster, Kai; Hansen, Jens Würgler; Bak, Friedhelm (January 1993). "Bacterial Disproportionation of Elemental Sulfur Coupled to Chemical Reduction of Iron or Manganese". Applied and Environmental Microbiology. 59 (1): 101–108. doi:10.1128/aem.59.1.101-108.1993. ISSN   0099-2240. PMC   202062 .
  7. ↑ Habicht, Kirsten S; Canfield, Donald E; Rethmeier, J̈org (August 1998). "Sulfur isotope fractionation during bacterial reduction and disproportionation of thiosulfate and sulfite". Geochimica et Cosmochimica Acta. 62 (15): 2585–2595. doi:10.1016/s0016-7037(98)00167-7. ISSN   0016-7037.
  8. ↑ Böttcher, M.E.; Thamdrup, B.; Vennemann, T.W. (May 2001). "Oxygen and sulfur isotope fractionation during anaerobic bacterial disproportionation of elemental sulfur". Geochimica et Cosmochimica Acta. 65 (10): 1601–1609. doi:10.1016/s0016-7037(00)00628-1. ISSN   0016-7037.
  9. 1 2 3 Tsang, Man-Yin; Böttcher, Michael Ernst; Wortmann, Ulrich Georg (2023-08-20). "Estimating the effect of elemental sulfur disproportionation on the sulfur-isotope signatures in sediments". Chemical Geology. 632: 121533. doi:10.1016/j.chemgeo.2023.121533. ISSN   0009-2541.
  10. ↑ Charlie Harding, David Arthur Johnson, Rob Janes, (2002), Elements of the P Block, Published by Royal Society of Chemistry, ISBN   0-85404-690-9
  11. ↑ Book: Non-Aqueous Media, exact reference of this book is lacking: need to be completed!.
  12. ↑ Hendrix, Katrien; Bleyen, Nele; Mennecart, Thierry; Bruggeman, Christophe; Valcke, Elie (2019). "Sodium azide used as microbial inhibitor caused unwanted by-products in anaerobic geochemical studies". Applied Geochemistry. 107: 120–130. doi:10.1016/j.apgeochem.2019.05.014. ISSN   0883-2927.
  13. 1 2 José Jiménez Barberá; Adolf Metzger; Manfred Wolf (2000). "Sulfites, Thiosulfates, and Dithionites". Ullmann's Encyclopedia of Industrial Chemistry . Weinheim: Wiley-VCH. doi:10.1002/14356007.a25_477. ISBN   978-3527306732.
  14. ↑ 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.
  15. ↑ Cowie, J. M. G. (1991). Polymers: Chemistry & Physics of Modern Materials (2nd ed.). Blackie. p. 58. ISBN   0-216-92980-6.
  16. ↑ Krebs, H.A. (1937). "LXXXVIII - Dismutation of pyruvic acid in gonoccus and staphylococcus". Biochem. J. 31 (4): 661–671. doi:10.1042/bj0310661. PMC   1266985 . PMID   16746383.
  17. ↑ Biochemical basis of mitochondrial acetaldehyde dismutation in Saccharomyces cerevisiae
  18. ↑ Bak, Friedhelm; Cypionka, Heribert (1987). "A novel type of energy metabolism involving fermentation of inorganic sulphur compounds". Nature. 326 (6116): 891–892. Bibcode:1987Natur.326..891B. doi:10.1038/326891a0. PMID   22468292. S2CID   27142031.
  19. ↑ Goldhaber, M.B.; Kaplan, I.R. (April 1980). "Mechanisms of sulfur incorporation and isotope fractionation during early diagenesis in sediments of the gulf of California". Marine Chemistry. 9 (2): 95–143. doi:10.1016/0304-4203(80)90063-8. ISSN   0304-4203.
  20. ↑ Sim, Min Sub; Bosak, Tanja; Ono, Shuhei (July 2011). "Large Sulfur Isotope Fractionation Does Not Require Disproportionation". Science. 333 (6038): 74–77. doi:10.1126/science.1205103. ISSN   0036-8075.
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