Determination of dissociation constants of p-hydroxybenzophenone in aqueous-organic mixtures. Solvent effects

SANCHO, M.I; BLANCO, S. E.; JUBERT, A.H.; FERRETTI, F.H.; CASTRO, E.A.

National Research Press- Canada

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 (acetonitrile-water, ethanol-water, and methanol-water), 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 Hardcastle-Jano 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