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 treating phenol with sodium hydroxide to form sodium phenoxide, 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).

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.