To a solution of 3.2 g of 5-aminosalicylic acid and 4.4 g of sodium carbonate in 60 ml of water (stirred vigourously at room temperature) is added dropwise a solution of 2.5 g of 5-nitroisophthaloyl chloride in a minimum amount of acetonitrile with formation of a gel. The gel is dissolved by acidification with dilute hydrochloric acid and a gray solid is formed. The material is filtered, washed once with dilute hydrochloric acid and several times with water resulting in a gray gum. The gum is crystallized by evaporation with ethanol to give a gray solid. The solid is boiled with ethanol, filtered and dried by conventional means to yield 2.76 g of the product of the example as a light brown powder.
