An LFER study of the protolytic equilibria of 4-aryl-2,4-dioxobutanoic acids in aqueous solutions

Verbic, T.Z., Drakulic, B.J., Zloh, M., Pecelj, J., Popovic, G. and Juranic, I.O. (2007) An LFER study of the protolytic equilibria of 4-aryl-2,4-dioxobutanoic acids in aqueous solutions. Journal of the Serbian Chemical Society, 72 (12). pp. 1201-1216. 10.2298/JSC0712201V.

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DOI: 10.2298/JSC0712201V

Abstract

The protolytic equilibria of 13 4-aryl-2,4-dioxobutanoic acids (ADKs) were spectrophotometrically studied in aqueous solutions in the pH range 1-9 at 25±1°C and an ionic strength of 0.1 mol l-1 (NaCl), with the exception of the 4-OH-derivative which was also potentiometrically studied in the pH range 7-10 at 25±1°C and an ionic strength of 0.1 mol l-1 (NaCl). In solution, the compounds simultaneously exist in one diketo and two enolic forms; therefore, the determined acidity constants (pZa1 1.87-2.29, pKa2 6.63-8.13 and pKa3(4-OH-) 9.52) represent system macro constants. The 1H-NMR spectrum of the parent compound (4-phenyl-2,4-dioxobutanoic acid) (25°C, pD 5.0) proved the existence of all tautomeric forms. Using the extended Hammett relation, the determined pKa values were correlated with literature σ values. The predicted pKa values were in fair accordance with the experimentally observed ones. Molecular, monoanionic and dianionic forms of the parent compound were optimized by the semi-empirical molecular orbital PM6 method using the implicit water solvation model (COSMO). The obtained geometries were used to explain the quality of the LFER models.

Item Type:Article
Uncontrolled Keywords:4-Aryl-2,4-dioxobutanoic acids (ADK); Acidity constants; Linear free energy relationship (LFER)
Departments, units and centres:Department of Pharmaceutical and Biological Chemistry > Department of Pharmaceutical and Biological Chemistry
ID Code:3047
Journal or Publication Title:Journal of the Serbian Chemical Society
Deposited By:Library Staff
Deposited On:23 Mar 2012 09:52
Last Modified:23 Mar 2012 09:52

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