Kolbe electrolysis

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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:

Contents

Electrolisis 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.svg

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 supressed, by performing the reaction under weakly acidic conditions in protic solvents, and using a high curent 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]

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 ; Collected Volumes, vol. 5, p. 445.
  4. 1 2 3 4 Bohn, Martin A.; Paul, Anna; Hilt, Gerhard (15 March 2012). "Electrochemically initiated radical reactions". Encyclopedia of Radicals in Chemistry, Biology and Materials. Vol. 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 (31 October 2022). Overcoming the Limitations of Kolbe Coupling via Waveform-Controlled Electrosynthesis (Report). Chemistry. doi: 10.26434/chemrxiv-2022-3cj82-v2 .
  6. ↑ Hioki, Yuta; Costantini, Matteo; Griffin, Jeremy; Harper, Kaid C.; Merini, Melania Prado; Nissl, Benedikt; Kawamata, Yu; Baran, Phil S. (7 April 2023). "Overcoming the limitations of Kolbe coupling with waveform-controlled electrosynthesis" . Science. 380 (6640): 81–87. Bibcode:2023Sci...380...81H. doi:10.1126/science.adf4762. ISSN   0036-8075. PMID   37023204.
  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; Galla, Ulrich; Schmieder, Helmut; Steckhan, Eberhard (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; Wang, Qingfa (18 January 2020). "Kolbe Electrolysis of Biomass-Derived Fatty Acids Over Pt Nanocrystals in an Electrochemical Cell" . ChemCatChem. 12 (2): 642–648. doi:10.1002/cctc.201901443. ISSN   1867-3880.
  11. ↑ Ho, Calvin K.; McAuley, Kimberley B.; Peppley, Brant A. (1 October 2019). "Biolubricants through renewable hydrocarbons: A perspective for new opportunities" . Renewable and Sustainable Energy Reviews. 113 109261. doi:10.1016/j.rser.2019.109261. ISSN   1364-0321.
  12. ↑ Andrieux, Claude P.; Gonzalez, Felipe; Savéant, Jean-Michel (1 May 1997). "Derivatization of Carbon Surfaces by Anodic Oxidation of Arylacetates. Electrochemical Manipulation of the Grafted Films" . Journal of the American Chemical Society. 119 (18): 4292–4300. doi:10.1021/ja9636092. ISSN   0002-7863.
  13. ↑ Bélanger, Daniel; Pinson, Jean (20 June 2011). "Electrografting: a powerful method for surface modification" . Chemical Society Reviews. 40 (7): 3995–4048. doi:10.1039/C0CS00149J. ISSN   1460-4744. PMID   21503288.

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