[Studies on Xipamide (4-chloro-5-sulfamoyl-2',6'-salicyloxylidide). Part 1: Physico-chemical and chemical properties (author's transl)].

The saluretic agent xipamide (4-chloro-5-sulfamoyl-2',6'-salicyloxylidide; Aquaphor) is a lipophilic substance as demonstrated by solubilities and partition coefficients. In the physiological pH-range, however, xipamide forms an anion which has an octanol-water partition coefficient of approx. 1. Two steps of ionization were investigated photometrically. The first one gives rise to a phenolate anion; pKa1 = 4.75. In the second one, ionization of the sulfamoyl group occurs; pKa2 = 10. Xipamide is stable in acidic as well as in basic media at room temperature. But when xipamide is acted upon by strong alkali and elevated temperature, 2,6-xylidine is formed by hydrolysis. For analytic use UV-photometric, colorimetric and TLC data of xipamide are given.