Determination of protonation macro- and microconstants and octanol/water partition coefficient of the antiinflammatory drug niflumic acid

Studies on equilibrium of anthranilic acid in aqueous solutions and in two-phase systems: Aromatic solvent–water

“…They applied this method for pyridoxine in dioxane -water system. The method was slightly modified and applied for niflumic acid in methanol -water and dioxane -water systems [20]. The obtained results for both investigated systems were in good agreement.…”

“…14 niflumic acid (∆pk = 0.90) [20]. This fact suggests that in the case of the investigated compound there are strong interactions between the two dissociation sites.…”

“…For this type of molecule with two ionizable groups connected to the chromophores, the microconstant could be determined by measuring the tautomeric ratios spectrophotometrically from mixture of organic compounds and water at the pH of the isoelectric point. This method was found and validated by Takács-Novák and co-workers [20,32,33]. The microconstants of anthranilic acid were determined on the basis of this method with the assumption that the spectrum of anthranilic acid in methanol is identified as that of the unionized form HR o while the spectrum in aqueous buffer at pH of the isoelectric point (3.51) is assigned to that of the zwitterion HR ± .…”

“…The tautomerization microconstant K z can be calculated from the spectroscopic data using the following Eq. [20,32,34]:…”

Ionization and Partitioning Profiles of Zwitterions: The case of the anti‐inflammatory drug azapropazone

“…In contrast, the spectra in dioxane showed several ill-defined isosbestic points (Fig. 6), indicating the presence of at least two tautomeric equilibria, namely zwitterion-neutral [20] and ketoenol. IR Spectra in DMSO.…”