Title: Acid Dissociation Constants of Sulfanilamides and Substituent Effect on the Constant
Abstract: Dissociation constants (pKa) of 12 commercial sulfanilamides were determined precisely by the spectrophotometric method at 27±1° and the ionic strength of 0.2. The compounds and their pKa values are: sulfapyridine 3.56, sulfisomidine 7.49, sulfathiazole 7.23, sulfamethoxypyridazine 7.17, sulfamerazine 6.85, sulfadiazine 6.37, sulfadimethoxine 5.98, sulfaphenazole 5.89, sulfisomezole 5.72, sulfamethizole 5.22, sulfisoxazole 4.79 and N-sulfanilyl-3, 4-xylamide 4.37.Effect of a substituent in the heterocyclic ring of sulfanilamides on pKa is discussed by correlating it with Hammett's sigma constant, σ.