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Basicity, Ionic Associations and their Effect on Solubility of the Antineoplastic Benflurone

F. Kopecký and B. Kopecká

Department of Physical Chemistry of Drugs, Faculty of Pharmacy, Comenius University, SK-832 32 Bratislav


Abstract: Associations of benflurone, i.e. 5-(2-dimethylammonioethoxy)-7-oxo-7H-benzo[c]fluorene chloride, were studied by UV VIS spectrophotometry in aqueous solutions and its pKa = 7.51 was determined by potentiometry. The UV VIS spectra of the acidified benflurone solutions simulated the second protonation, but it was disproved by the IR spectra of the prepared crystalline salt of the benflurone base (B) B2(HClO4)3. Multiple association equilibria were evidenced, in diluted aqueous solutions they started with dimerization of the benflurone cations. On the addition of increasing excess of KCl (or another strong electrolyte), gradual formation of ion pairs BH+Cl-, their dimers (BH+Cl-)2, and higher colloidal associates was manifested, after some time followed by the precipitation. The determined association constants showed that the preferred associate in the diluted solution was the dimer (BH+)2 of the amphiphilic benflurone cations. The unusually sharp solubility decrease observed on the addition of KCl indicated that while the cationic dimerization supported the benflurone solubility, the uncharged ion pairs and their multimers were very poorly soluble.

Full paper in Portable Document Format: 512a99.pdf


Chemical Papers 51 (2) 99–106 (1997)

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