oa South African Journal of Chemistry - Determination of the Protonation Constants of Some 4-(Substituted benzylamino)-4,5-dihydro-1H-1,2,4-triazol-5-ones by the Potentiometric Method in Ethanol-Water Mixtures
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 MNaCl 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 pKa 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 title 4, 5-dihydro- 1H-1, 2, 4-triazol-5-ones decreased linearly with increasing ethanol content, but the values determined with 80% ethanol did not follow this linear trend. The variation of these constants is discussed on the basis of specific solute-solvent interactions.
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