Аннотация:In this work, a study of homogeneous carboxylation of potassium, sodium and lithium phenolates in DMSO solution at 100 °C by the Kolbe-Schmitt reaction was conducted. The influence of water, phenolate concentration, and cation nature on the yield of products and reaction selectivity was shown. Based on the shape of the dependencies, a conclusion was made about a complex cluster mechanism of the carboxylation reaction in solution. The use of a homogeneous reaction medium allows convenient testing of various additives to study their effect on the reaction, in particular, such basic additives as sodium salts of mesitol, tert-butylcalix[4]arene, sodium isopropyl and tert-butyl carbonates have a promoting effect, increasing the yield of hydroxybenzoic acids on 20% (to 61.6%). It was found that in DMSO solution, the main reaction product is 4-hydroxybenzoic acid, while the classical Kolbe-Schmitt method leads to 2-hydroxybenzoic (salicylic) acid. Using 13C NMR spectroscopy, the spectrum of a “carbonate complex” in solution was obtained for the first time, where the chemical shift value of the carbonate carbon is 142 ppm, which is unusual for stable carbonates and is located between the signals of free dissolved CO2 and carboxylate derivatives.
