Physics:Kolbe electrolysis

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Short description: Organic reaction
"Kolbe reaction" redirects here. For the carboxylation of phenols, see Kolbe–Schmitt reaction.


The Kolbe electrolysis or Kolbe reaction is an organic reaction named after Hermann Kolbe.[1] The Kolbe reaction is formally a decarboxylative dimerisation of two carboxylic acids (or carboxylate ions). The overall reaction is:

File:Electrólisis de Kolbe.png

Mechanism and side-reactions

The reaction mechanism involves a two-stage radical process: electrochemical oxidation first gives a alkylcarboxyl radical, which decarboxylates almost immediately to give an alkyl radical intermediate. The alkyl radicals which combine to form a covalent bond.[2] As an example, electrolysis of acetic acid yields ethane and carbon dioxide:

CH3COOH → CH3COO− → CH3COO· → CH3· + CO2
2CH3· → CH3CH3

Another example is the synthesis of 2,7-dimethyl-2,7-dinitrooctane from 4-methyl-4-nitrovaleric acid:[3]

Kolbe electrolysis, synthesis of 2,7-Dimethyl-2,7-dinitrooctane

Other compounds can trap the radicals formed by decarboxylation, and the Kolbe reaction has also been occasionally used in cross-coupling reactions. If a mixture of two different carboxylates are used, the radical cross-coupling reaction generally gives all combinations of them:[4]

R1COO− + R2COO− → R1−R1 and/or R1−R2 and/or R2−R2

The reaction process can be enhanced and the Hofer–Moest reaction alternative suppressed, by performing the reaction under weakly acidic conditions in protic solvents, and using a high current density and a platinum anodic electrode.[4]

In 2022, it was discovered that the Kolbe electrolysis is enhanced if an alternating square wave current is used instead of a direct current.[5][6]

Hofer–Moest reaction

In the Hofer–Moest reaction, the alkyl radical undergo further oxidation to form a carbocation, rather than coupling with another alkyl radical, which then reacts with an available nucleophile.[7] The Hofer–Moest reaction, rather than Kolbe radical-coupling, always occurs if the carboxylic acid bears a carbocation-stabilizing side-substituent at the α position, but only sometimes otherwise.[4]

File:Hofer-Moest-reaction.svg

Applications

Kolbe electrolysis has a few industrial applications.[8] The reaction typically yields <50%.[4]

In one example, sebacic acid has been produced commercially by Kolbe electrolysis of adipic acid.[9]

Kolbe electrolysis has been examined for converting biomass into biodiesel[10][11] and for grafting of carbon electrodes.[12][13]

See also

References

  1. ↑ Utley, James (1997). "Trends in Organic Electrosynthesis". Chemical Society Reviews 26 (3): 157. doi:10.1039/cs9972600157. 
  2. ↑ Vijh, A. K.; Conway, B. E. (1967). "Electrode Kinetic Aspects of the Kolbe Reaction". Chem Rev 67 (6): 623–664. doi:10.1021/cr60250a003. 
  3. ↑ Sharkey, W. H.; Langkammerer, C. M. (1973). "2,7-Dimethyl-2,7-dinitrooctane". Organic Syntheses. http://www.orgsyn.org/demo.aspx?prep=cv5p0445. ; Collective Volume, 5, pp. 445 
  4. ↑ 4.0 4.1 4.2 4.3 Bohn, Martin A.; Paul, Anna; Hilt, Gerhard (15 March 2012). "Encyclopedia of Radicals in Chemistry, Biology and Materials". Encyclopedia of Radicals in Chemistry, Biology and Materials. Synthetic Strategies and Applications. Wiley. § 2.7. doi:10.1002/9781119953678.rad034. ISBN 978-0-470-97125-3. 
  5. ↑ Hioki, Yuta; Costantini, Matteo; Griffin, Jeremy; Harper, Kaid; Prado Merini, Melania; Nissl, Benedikt; Kawamata, Yu; Baran, Phil (2022-10-31). Overcoming the Limitations of Kolbe Coupling via Waveform-Controlled Electrosynthesis (Report). Chemistry. doi:10.26434/chemrxiv-2022-3cj82-v2. https://chemrxiv.org/engage/chemrxiv/article-details/635afdb2ca86b81d1ac683f4. 
  6. ↑ Hioki, Yuta; Costantini, Matteo; Griffin, Jeremy; Harper, Kaid C.; Merini, Melania Prado; Nissl, Benedikt; Kawamata, Yu; Baran, Phil S. (2023-04-07). "Overcoming the limitations of Kolbe coupling with waveform-controlled electrosynthesis" (in en). Science 380 (6640): 81–87. doi:10.1126/science.adf4762. ISSN 0036-8075. PMID 37023204. Bibcode: 2023Sci...380...81H. https://www.science.org/doi/10.1126/science.adf4762. 
  7. ↑ "Hofer–Moest Reaction". Comprehensive Organic Name Reactions and Reagents. 2010. pp. 1443–1446. doi:10.1002/9780470638859.conrr322. ISBN 978-0-471-70450-8. 
  8. ↑ Wendt, Hartmut; Vogt, Helmut; Kreysa, Gerhard; m. Kolb, Dieter; e. Engelmann, Gerald; Ziegler, Jörg C.; Goldacker, Hubert; Jüttner, Klaus et al. (2009). "Electrochemistry". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a09_183.pub3. ISBN 978-3-527-30673-2. 
  9. ↑ Seko, Maomi; Yomiyama, Akira; Isoya, Toshiro (1979). "Development of Kolbe Electrosynthesis of Sebacic Acid". CEER, Chemical Economy & Engineering Review 11 (9): 48–50. 
  10. ↑ Yuan, Gang; Wu, Chan; Zeng, Guorong; Niu, Xiaopo; Shen, Guoqiang; Wang, Li; Zhang, Xiangwen; Luque, Rafael et al. (2020-01-18). "Kolbe Electrolysis of Biomass-Derived Fatty Acids Over Pt Nanocrystals in an Electrochemical Cell" (in en). ChemCatChem 12 (2): 642–648. doi:10.1002/cctc.201901443. ISSN 1867-3880. https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/cctc.201901443. 
  11. ↑ Ho, Calvin K.; McAuley, Kimberley B.; Peppley, Brant A. (2019-10-01). "Biolubricants through renewable hydrocarbons: A perspective for new opportunities". Renewable and Sustainable Energy Reviews 113. doi:10.1016/j.rser.2019.109261. ISSN 1364-0321. https://www.sciencedirect.com/science/article/pii/S1364032119304691. 
  12. ↑ Andrieux, Claude P.; Gonzalez, Felipe; Savéant, Jean-Michel (1997-05-01). "Derivatization of Carbon Surfaces by Anodic Oxidation of Arylacetates. Electrochemical Manipulation of the Grafted Films" (in en). Journal of the American Chemical Society 119 (18): 4292–4300. doi:10.1021/ja9636092. ISSN 0002-7863. https://pubs.acs.org/doi/10.1021/ja9636092. 
  13. ↑ Bélanger, Daniel; Pinson, Jean (2011-06-20). "Electrografting: a powerful method for surface modification" (in en). Chemical Society Reviews 40 (7): 3995–4048. doi:10.1039/C0CS00149J. ISSN 1460-4744. PMID 21503288. https://pubs.rsc.org/en/content/articlelanding/2011/cs/c0cs00149j. 

Further reading

| title = Untersuchungen über die Elektrolyse organischer Verbindungen
|trans-title= Investigations of the electrolysis of organic compounds
| first = Hermann |last= Kolbe
| journal = Annalen der Chemie und Pharmacie
| year = 1849
| volume = 69
| issue = 3
| pages = 257–294
| url = https://babel.hathitrust.org/cgi/pt?id=hvd.hx3bh3;view=1up;seq=271
| doi =  10.1002/jlac.18490690302



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