Abstract
N, N-Dimethylformamide (DMF) was previously found to serve as a good solvent for the carboxylation of alkali phenoxides with carbon dioxide into hydroxybenzoic acids. Thus, in the present study, the carboxylation of phenol in DMF under carbon dioxide pressure in the presence of various metal carbonates was studied. Of the alkali metal carbonates, potassium carbonate was particularly effective.The effects of the amount of potassium carbonate, reaction temperatures, reaction time and the initial pressure of carbon dioxide upon the yield of hydroxybenzoic acids including 4-hydroxyisophthalic acid were studied. The ratio of the p-isomer to the o-isomer formed was then clarified. The stability of p-hydroxybenzoic acid, salicylic acid, and their potassium salts in DMF at high temperatures was also tested. Vigorous evolution of carbon dioxide was noted when they were heated at 280°C and the product consisted predominantly of salicylic acid. Dipotassium salicylate, however, remained unchanged under such conditions.
