Kolbe–Schmitt reaction

The Kolbe–Schmitt reaction or Kolbe process (named after Hermann Kolbe and Rudolf Schmitt) is a carboxylation chemical reaction that proceeds by heating sodium phenoxide (the sodium salt of phenol) with carbon dioxide under pressure (100 atm, 125 °C), then treating the product with sulfuric acid. The final product is an aromatic hydroxy acid which is also known as salicylic acid (the precursor to aspirin).[1][2][3][4]

The Kolbe–Schmitt reaction
"Kolbe process" redirects here. For the electrochemical decarboxylation/dimerization reaction, see Kolbe electrolysis.

Kolbe–Schmitt reaction
Named after Hermann Kolbe
Rudolf Schmitt
Reaction type Addition reaction
Identifiers
Organic Chemistry Portal kolbe-schmitt-reaction
RSC ontology ID RXNO:0000182

By using potassium hydroxide, 4-hydroxybenzoic acid is accessible, an important precursor for the versatile paraben class of biocides used e.g. in personal care products.

The methodology is also used in the industrial synthesis of 3-hydroxy-2-naphthoic acid. The regiochemistry of the carboxylation in this case is sensitive to temperature.[5]

Reaction mechanism

The Kolbe–Schmitt reaction proceeds via the nuecliophillic addition of a phenoxide, classically sodium phenoxide (NaOC6H5), to carbon dioxide to give the salicylate. The final step is reaction of the salicylate with acid to form the desired salicylic acid.

Kolbe–Schmitt reaction mechanism

References
  1. Hermann Kolbe (1860). "Ueber Synthese der Salicylsäure" [On the synthesis of salicylic acid]. Annalen der Chemie und Pharmacie. 113 (1): 125–127. doi:10.1002/jlac.18601130120.
  2. R. Schmitt (1885). "Beitrag zur Kenntniss der Kolbe'schen Salicylsäure Synthese" [Contribution to [our] knowledge of Kolbe's synthesis of salicylic acid]. Journal für Praktische Chemie. 2nd series. 31 (1): 397–411. doi:10.1002/prac.18850310130.
  3. A. S. Lindsey and H. Jeskey (1957). "The Kolbe-Schmitt Reaction". Chem. Rev. 57 (4): 583–620. doi:10.1021/cr50016a001. (Review)
  4. R. T. Morrison and R. N. Boyd (1983). Organic Chemistry (4th ed.). Allyn and Bacon. p. 976-7. ISBN 0-205-05838-8.
  5. Gerald Booth (2005). "Naphthalene Derivatives". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a17_009. ISBN 3527306730..
  • English Translation of Kolbe's seminal 1860 German article in Annalen der Chemie und Pharmacie that describes the discovery of this reaction. English title: 'On the syntheses of salicylic acid'; German title "Ueber Synthese der Salicylsäure".
  • An animation of the reaction mechanism.
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