Effect of solvents on the PKa values of some sulpha drugs

ABSTRACT

In the present investigation the ionization constants of sulfapyridine, sulfadimidine, sulfasomidine, sulfapyridazine, sulfamerazine, sulfadiazine and sulfamethoxazole were determined potentiometrically using five solvents with concentration ranging between 20 to 100%. Concerning with the solvents used the following regularity in PKa of different sulfa-drugs can be noted Dioxane > dimethyl-formamide > methanol ethanol > acetone. The number of the solvent molecules [n] surrounding each drug molecule was determined. An attempt was made to detect the number of water molecules in the primary and secondary solvation zone [J] for the different solvent mixtures. Moreover, the relationship between the viscosity of three sulfa-drugs in ethanol-water mixture and their percentage have been evaluated