Synthesis of novel bis-thiourea derivatives and potentiometric andspectrophotometric determination of their acid dissociation constants

Within the scope of the study, two bis-thiourea derivative compounds (30a, 30b) were synthesized and their molecular structures were characterized by using NMR, FT-IR, and HRMS. Acid dissociation constants of the compounds were determined both potentiometrically and spectrophotometrically in the acidic medium at 25.0 ± 0.1 °C, 0.1 M NaCl ionic strength, and DMSO: water (50:50 v/v) hydro-organic solvent system. The pKa values, which may belong to the enthiol groups, of compounds 30a and 30b were determined as 7.06±0.13 and 6.94±0.11 potentiometrically, respectively, and 7.11±0.08 and 7.05±0.01 spectrophotometrically. The pKa values, which may belong to the NH groups, of the 30a and 30b compounds were determined as 12.11±0.06 and 11.17±0.06 potentiometrically, respectively, and 12.30±0.08 and 11.82±0.02 spectrophotometrically. In addition, it can be said that the pKa values determined as 3.56±0.08 and 3.87±0.01 spectrophotometrically, respectively, may belong to the enol groups of 30a and 30b compounds, respectively.