CEQUINOR   05415
CENTRO DE QUIMICA INORGANICA "DR. PEDRO J. AYMONINO"
Unidad Ejecutora - UE
artículos
Título:
Determination of dissociation constants of p-hydroxybenzophenone in aqueous-organic mixtures. Solvent effects
Autor/es:
M. I. SANCHO; A,H.JUBERT; S. E. BLANCO; F.H.FERRETTI; E.A.CASTRO
Revista:
Canadian Journal of Chemistry
Referencias:
Año: 2008 vol. 86 p. 462 - 469
Resumen:
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.