Determination of acidic constants of some phenyl-hydroxyiminoethyl quinolinium compounds

Abstract

Mixed acidic constants (pK′a) of quinolinium oximes [1-(2-phenyl-2-hydroxyiminoethyl)-1-quinolinium chloride (F-1), 1-(2-phenyl-2-hydroxyiminoethyl)-1-isoquinolinium chloride (F-2), 1-(2-phenyl-2-hydroxyiminoethyl)-1-(4′-methyl)-quinolinium chloride (F-3), and 1-(2-phenyl-2-hydroxyiminoethyl)-1-(6′-methyl)-quinolinium chloride (F-4)] have been determined via their UV absorption spectra recorded in the series of Britton-Robinson's buffer solutions in the pH region 8.74-11.28 (t=25±0.5°C, μ=0.2). The obtained pK′a values are in good agreement with those achieved by applying graphical methods. The following pK′a values have been obtained: 9.93 for F-1, 9.90 for F-2, and 10.02 for F-3 and F-4. On the basis of potentiometric titrations thermodynamic acidic constants (pKa) of compounds F-1, F-2, F-3, and F-4 have been determined and they were found to be 9.82, 9.71, 9.91, and 9.86, respectively. The values obtained by transferring pKa into pK′a are in good agreement with the values obtained spectrophotometrically.