Factors influencing the formation of 2-hydroxy-6-naphthoic acid from carboxylation of naphthol

The synthesis of 2-hydroxy-6-naphthoic acid (2,6-HNA) from carboxylation of alkali-naphthoxide was studied with varying alkali cation types and reaction conditions such as reactant concentration, reaction time, temperature, and pressure. The product selectivity was strongly affected by the types of alkali cation, reaction time, and temperature, while the product yield was governed by reaction pressure. The maximum HNA yield, 28.6%, was achieved with 2,6-HNA selectivity of 81.6% at 6 atm of CO₂, 543 K, and 6 h of reaction. The addition of K₂CO₃ led to further increase in the productivity of 2,6-HNA via suppression of the decarboxylation of HNA.