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

Determination of pK_a values of the active constituent of certain pharmaceutical preparations is important because the distribution, transport behaviour, bonding to receptors, and contributions to the metabolic behaviour of the active constituent molecules depend on the ionization constant. It is known that 1,2,4-triazole and 4,5-dihydro-1H-1,2,4-triazol-5-one rings have weak acidic properties, so that some 1,2,4-triazole and 4,5-dihydro-1H-1,2,4-triazol-5-one derivatives were titrated potentiometrically with tetrabutyl ammonium hydroxide (TBAH) in non-aqueous solvents, and the pK_a values of the compounds were determined. In this study, the first part of the study nine novel 3-alkyl(aryl)-4-[3-etoxy-4-(4-methoxybenzensulfonyloxy)-benzylidenamino]-4,5-dihydro-1H-1,2,4-triazol-5-ones were synthesized from the reactions of the corresponding 3-alkyl(aryl)-4-amino-4,5-dihydro-1H-1,2,4-triazol-5-ones with 2-ethoxy-4-formylphenyl 4-methoxybenzenesulfonate, which was obtained from the reaction of 3-ethoxy-4-hydroxybenzaldehyde with 4-methoxybenzensulfonyl chloride by using triethylamine. The new compounds synthesized were also characterized by using IR and ¹H-NMR, ¹³C-NMR spectral data. The second part of the study, nine novel 3-alkyl(aryl)-4-[3-etoxy-4-(4-methoxybenzensulfonyloxy)-benzylidenamino]-4,5-dihydro-1H-1,2,4-triazol-5-ones were titrated potentiometrically with TBAH (tetrabutylammonium hydroxide) in four different non-aqueous solvents (isopropyl alcohol, tert-butyl alcohol, acetone and N,N-dimethylformamide) and graphs were drawn for all cases. The half notralization potentials and pK_a values were determined by half neutralization method. The effects of solvents and molecular structure upon acidity were also discussed.

Keywords

• Synthesis
• 4
• 5-dihydro-1H-1
• 2
• 4-triazol-5-one
• TBAH
• pKa
• Half-neutralization method

References

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