Synthesis and Potentiometric Titrations of 3-Alkyl(Aryl)-4-[3-etoxy-4-(4-methoxybenzensulfonyloxy)-benzylidenamino]-4,5-dihydro-1H-1,2,4-triazol-5-ones

Abstract

Determinationof pKa values of theactive constituent of certain pharmaceutical preparations is important becausethe distribution, transport behaviour, bonding to receptors, and contributionsto the metabolic behaviour of the active constituent molecules depend on theionization constant. It is known that 1,2,4-triazole and4,5-dihydro-1H-1,2,4-triazol-5-one rings have weak acidic properties, so thatsome 1,2,4-triazole and 4,5-dihydro-1H-1,2,4-triazol-5-one derivatives weretitrated potentiometrically with tetrabutyl ammonium hydroxide (TBAH) innon-aqueous solvents, and the pKa values of thecompounds were determined. In this study, the first part of the study ninenovel3-alkyl(aryl)-4-[3-etoxy-4-(4-methoxybenzensulfonyloxy)-benzylidenamino]-4,5-dihydro-1H-1,2,4-triazol-5-ones were synthesizedfrom the reactions of the corresponding 3-alkyl(aryl)-4-amino-4,5-dihydro-1H-1,2,4-triazol-5-ones with2-ethoxy-4-formylphenyl 4-methoxybenzenesulfonate, which was obtained from thereaction of 3-ethoxy-4-hydroxybenzaldehyde with 4-methoxybenzensulfonylchloride by using triethylamine. The new compounds synthesized were alsocharacterized by using IR and 1H-NMR, 13C-NMR spectraldata. The second part of the study, nine novel3-alkyl(aryl)-4-[3-etoxy-4-(4-methoxybenzensulfonyloxy)-benzylidenamino]-4,5-dihydro-1H-1,2,4-triazol-5-ones were titratedpotentiometrically with TBAH (tetrabutylammonium hydroxide) in four differentnon-aqueous solvents (isopropyl alcohol, tert-butyl alcohol, acetone and N,N-dimethylformamide) and graphs weredrawn for all cases. The half notralization potentials and pKa values were determined byhalf neutralization method. The effects of solvents and molecular structureupon acidity were also discussed.