A conventional coulometric titration method for the determination of a small amount of Sulfamethizole, Sulfaphenazole, and Sulfamethoxypyridazine (listed in the Pharmacopoeia of Japan, 8th Ed., 1971) was examined. Sulfamethizole, Sulfaphenazole, and Sulfamethoxypyridazine were brominated quantitatively with electrolytically generated bromine, in an aqueous hydrochloric acid-potassium bromide medium. The end point was detected by a potentiometer. Sulfamethizole and sulfamethoxypyridazine reacted with 2 moles of bromine and changed to their dibromides, 2-(3, 5-dibromosulfanilamido)-5-methyl-1, 3, 4-thiadiazole and 3-(3, 5-dibromosulfanilamido)-6-methoxypyridazine, respectively, while sulfaphenazole reacted with 3 moles of bromine and changed to its tribromide, 5-(3, 5-dibromosulfanilamido)-4-bromo-1-phenylpyrazole. The brominated position of these sulfonamides was checked by infrared and nuclearmagnetic resonance spectrograms.
