Synthesis and Determination of Acid Dissociation Constants of Bis-Acyl Thiourea Derivatives

N,N'-((dodecane-1,12-diylbis(azanediyl))bis(carbonothioyl))bis(4-nitrobenzamide) 5 and N,N'-((dodecane-1,12-diylbis(azanediyl))bis(carbonothioyl))bis(3-nitrobenzamide) 6 as bis acyl thiourea derivatives were synthesized and their molecular structures were characterized using 1H NMR, 13C NMR, COSY, DEPT, HMQC, FT-IR, and HRMS techniques. The acid dissociation constants (pKa) of the bis-acyl thiourea derivatives 5, 6 were determined potentiometrically and spectrophotometrically. The pKa values of products 5, 6 were determined in 50% (v/v) dimethyl sulfoxide–water hydro-organic solvent in the presence of 0.1 molL1 ionic strength of NaCl and in the acidic medium at 25±0.1 °C, and two pKa values were calculated for each compound with the HYPERQUAD computer program using the data obtained from the potentiometric titrations performed. In addition, three pKa values for each compound were determined in the calculations using the HypSpec program from the data obtained from the spectrophotometric titrations performed under the conditions where the potentiometric titrations were performed. For compounds 5 and 6, spectrophotometrically, pKa1 was 3.56±0.08 and 3.87±0.01, respectively, pKa2 was 7.11±0.08 and 7.05±0.01, respectively, and pKa3 was 12.30±0.08 and 11.82±0.02, respectively. It can be said that pKa1, pKa2, and pKa3 values may belong to enol, enthiol, and NH, respectively. Moreover, for compounds 5 and 6, potentiometrically, pKa2 was 7.06±0.13 and 6.94±0.11, respectively, and pKa3 was 12.11±0.06 and 11.17±0.06, respectively, and it can be said that pKa2 and pKa3 values may belong to enthiol and NH, respectively. It is seen that the pKa values determined spectrophotometrically and potentiometrically are compatible with each other.