Abstract
Carboxylation of 2-naphthol with carbon dioxide in anisole at high temperature yields 3-hydroxy-2-naphthoic acid and 6-hydroxy-2-naphthoic acid, which are difficult to synthesize by the Kolbe-Schmitt reaction. The synthesis of 6-hydroxy-2-naphthoic acid by the carboxylation of 2-naphthol with carbon dioxide in kerosene was investigated, in particular the influence of the reaction conditions, such as reaction time and reaction temperature, and the alkali metal cations of the naphthoxides. The yield of all hydroxynaphthoic acids from potassium 2-naphthoxide was higher than that from sodium 2-naphthoxide. Carboxylation of sodium 2-naphthoxide yielded small amounts of 6-hydroxy-2-naphthoic acid, whereas the potassium salt provided high selectivity for 6-hydroxy-2-naphthoic acid. Reaction conditions had little effect on product yield. In the temperature range of 513 K to 573 K, however, the yield of 3-hydroxy-2-naphthoic acid decreased and that of 6-hydroxy-2-naphthoic acid increased with higher temperature. Based on the results of thermal rearrangement and thermal decomposition profile of the product, the dependence of product selectivity on reaction temperature was primarily attributable to the thermostability of the product. This finding indicated that selective synthesis of 6-hydroxy-2-naphthoic acid could be successfully achieved by carboxylation of potassium naphthoxide in kerosene.
