The reaction mechanism of the Kolbe-Schmitt reaction of phenol and 2-naphthol has been investigated. An alkali metal phenoxide-CO2 complex is not an intermediate that can be easily transformed into a carboxylic acid, such as salicylic acid (SA) and p-hydroxybenzoic acid (pHBA). A direct carboxylation of phenoxide with CO2 takes place even at room temperature, and is competitive with the formation of the CO2 complex. The resulting complex decomposes thermally (above ca. 100 degrees C) to phenoxide, which then undergoes further competitive reactions. Experiments using a carbon-13 labeled complex support a mechanism of direct carboxylation, and not the mechanism via a CO2 complex. The reactivity, C-13 NMR and MOPAC/PM3 calculations suggest a new carbonate-like structure for the CO2 complex.

The reaction between potassium (or sodium) phenoxide and carbon dioxide at room temperature forms salicylic acid and p-hydroxybenzoic acid at the same time besides the complex, [alkali metal phenoxideÁCO 2 ]. The complex had been thought an intermediate of the Kolbe-Schmitt reaction but is found inactive to the carboxylation at terrestrial temperatures.

The carboxylation of alkali metal phenoxide with carbon dioxide gives not only ortho-but also para-hydroxybenzoic acids at room temperature, unlike the well-known Kolbe±Schmitt reaction.

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