Kolbe–Schmitt reaction | |
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Named after | |
Reaction type | Addition reaction |
Identifiers | |
Organic Chemistry Portal | kolbe-schmitt-reaction |
RSC ontology ID | RXNO:0000182 |
The Kolbe–Schmitt reaction or Kolbe process (named after Hermann Kolbe and Rudolf Schmitt) is a carboxylation chemical reaction that proceeds by treating phenol with sodium hydroxide to form sodium phenoxide, [1] then heating sodium phenoxide 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). [2] [3] [4] [5]
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. [6]
The Kolbe–Schmitt reaction proceeds via the nucleophilic addition of a phenoxide, classically sodium phenoxide (NaOC6H5), to carbon dioxide to give the salicylate. The final step is the reaction ( protonation) of the salicylate anion with an acid to form the desired salicylic acids (ortho- and para- isomers).