Determination of the Protonation Constants of Some 3-Alkyl(Aryl)-4-(Substitutebenzylamino)-4,5-Dihydro-1H-1,2,4-Triazol-5-ones by the Potentiometric Method in Ethanol-Water Mixtures

Abstract

To gain more information about the effect of solvent on 4,5-dihydro-1H-1,2,4-triazol-5-ones, the stoichiometric protonation constants of thirteen triazoles in ethanol-water mixtures were determined at an ionic strength of 0.10 M NaCl and at 25.0 ± 0.1 oC under nitrogen atmosphere. A potentiometric method was used and the calculation was carried out using the PKAS computer program. The corresponding pK_a values of these triazoles were determined in ethanol-water mixtures. Thus, the effects of solvent and molecular structure upon acidity were investigated. The logarithm of the protonation constants of the above-mentioned 4,5-dihydro-1H-1,2,4-triazol-5-ones linearly decreased with increases in ethanol contents but the values that determined 80% ethanol did not follow this linear trend. The variation of these constants is discussed on the basis of specific solute-solvent interactions.

Nigerian Journal of Chemical Research Vol. 11 2006: pp. 1-10