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Kolbe-Schmitt reaction

The Kolbe-Schmitt reaction/Kolbe process (named after Adolph Wilhelm Hermann Kolbe and Rudolf Schmitt) is a carboxylation chemical reaction that proceeds by heating sodium phenolate (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]

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

Reaction mechanism

The Kolbe-Schmitt reaction proceeds via the nucleophilic addition of a phenolate to carbon dioxide to give the salicylate. The final step is reaction of the salicylate with acid to form the desired salicylic acid.

References

^ Hermann Kolbe (1860). "Ueber Synthese der Salicylsäure". Annalen der Chemie und Pharmacie 113 (1): 125-127. doi:10.1002/jlac.18601130120.
^ R. Schmitt (1885). "Beitrag zur Kenntniss der Kolbe'schen Salicylsäure Synthese". Journal für Praktische Chemie 31 (1): 397-411. doi:10.1002/prac.18850310130.
^ A. S. Lindsey and H. Jeskey (1957). "The Kolbe-Schmitt Reaction". Chem. Rev. 57 (4): 583-620. doi:10.1021/cr50016a001. (Review)