Process for separation of 2-hydroxynapthalene-3-carboxylic acid from the reaction mixtures of alkali metal salts of 2-hydroxynaphthalene and carbon dioxide

摘要

In the carboxylation of 2-alkali metal naphtholates under pressure and at temperatures of above 200 DEG C., apart from the alkali metal salt of 2-naphthol-3-carboxylic acid and free 2-naphthol considerable amounts of resinous by-products are obtained which according to the hitherto known processes have to be separated and removed in a very expensive manner. According to this invention, the alkali-soluble acidic resins are separated from this carboxylation melt after its solution in water during the work-up of the carboxylation product by means of a cationic quaternary ammonium compound. These surface-active compounds precipitate the alkali-soluble acidic resins in such a manner that they can be easily removed from the alkali metal salts of 2-hydroxynaphthalene-3-carboxylic acid dissolved in water.