Potentiometric determination of the equilibrium constants for the formation of Fe(III)-sorbitol complexes

Potentiometric pH titration was used to study the interaction of Fe(III) with sorbitol with different ratios of Fe(In):sorbitol (6:1-1:1) in dilute aqueous solution at 25 degrees C. The results show that in the ratio of Fe(III):sorbitol-6:1 system, the FeH- 1L (L = sorbitol), Fe3H- 9L, Fe6H- 6L and Fe6H- 18L species are formed in the pH range about 2.3-3.7. From pH about 3.7-11 there is a solid region. At pH above 11 the precipitate is transformed to the water soluble Fe6H- 24L complex. The equilibrium data were processed with program BEST. Molecular modeling of the Fe6H- 18L complex indicates that the formation of an Fe(III)-sorbitol complex with a molar ratio of Fe(III) to sorbitol of 6:1 is possible. (C) 1999 Elsevier Science S.A. All rights reserved.