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

Abstract

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 1 H NMR, 13 C NMR, COSY, DEPT, HMQC, FT-IR, and HRMS techniques. The acid dissociation constants (p K a) of the bis-acyl thiourea derivatives 5, 6 were determined potentiometrically and spectrophotometrically. The pK a 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 p K a values were calculated for each compound with the HYPERQUAD computer program using the data obtained from the potentiometric titrations performed. In addition, three pK a 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, pK a1 was 3.56±0.08 and 3.87±0.01, respectively, pK a2 was 7.11±0.08 and 7.05±0.01, respectively, and pK a3 was 12.30±0.08 and 11.82±0.02, respectively. It can be said that pK a1, pK a2, and pK a3 values may belong to enol, enthiol, and NH, respectively. Moreover, for compounds 5 and 6, potentiometrically, pK a2 was 7.06±0.13 and 6.94±0.11, respectively, and pK a3 was 12.11±0.06 and 11.17±0.06, respectively, and it can be said that pK a2 and pK a3 values may belong to enthiol and NH, respectively. It is seen that the pK a values determined spectrophotometrically and potentiometrically are compatible with each other.