CENTRO DE QUIMICA INORGANICA "DR. PEDRO J. AYMONINO"
Unidad Ejecutora - UE
Determination of dissociation constants of p-hydroxybenzophenone in aqueous-organic mixtures. Solvent effects
M. I. SANCHO; A,H.JUBERT; S. E. BLANCO; F.H.FERRETTI; E.A.CASTRO
Canadian Journal of Chemistry
Año: 2008 vol. 86 p. 462 - 462
The apparent acidity constant of p-hydroxybenzophenone, which is a practically insoluble drug in water but of great pharmaceutical interest, was determined by reversed-phase high-performance liquid chromatography in organic solvent water mixtures (acetonitrilewater, ethanolwater, and methanolwater), varying the reaction medium permittivity in the interval 56 to 70, at constant ionic strength (0.050) and temperature (30 °C). A combined glass electrode calibrated with aqueous standard buffers was used to obtain pH readings based on the concentration scale (swpH). The pKa values from chromatographic data were obtained using the HardcastleJano equation. Moreover, excellent linear relationships between the pKa values and solvation properties of the reaction medium (relative permittivity and Acity) were used to derive acid dissociation constants in aqueous solution. It has been concluded that the pKa values extrapolated from such solventwater mixtures are consistent with each other and with previously reported measurements. In addition, the molecular structures of all the chemical species involved in the acidbase dissociation equilibrium studied were calculated with a B3LYP/6311++G(d,p) method that makes use of the polarizable continuum model (PCM). Taking into account the theoretical pKa values, the conclusions obtained match our experimental determinations.