Para-aminosalicylic acids

摘要

A pure, dense form of p-aminosalicylic acid is prepared by forming a solution of an alkali metal salt of the acid in a water-isopropanol medium and acidifying the solution to precipitate p-aminosalicylic acid. The salt can be dissolved in aqueous isopropanol, or, alternatively, can be dissolved in water and isopropanol added to the solution so formed, either before or as the solution is acidified. A surface-active agent may be added to the water-isopropanol medium. Any acid capable of precipitating p-aminosalicylic acid from a solution of an alkali metal salt thereof may be used, hydrochloric, sulphuric and formic acids being specified. The process of the invention is illustrated in examples, the following additional features being described (a) sodium bisulphite or hydrosulphite present in the water-isopropanol medium and (b) preliminary treatment of the aqueous salt solution with activated carbon.