Studies on the Interaction between Iron(III) and Glycerol or Related Polyols over a Wide pH Range

Abstract

Abstract The interaction between iron(III) and glycerol or related polyols was studied in some detail over a pH range of 1 to 13 mainly by spectrophotometric and NMR measurements. At acidic pH, there appeared a new absorption band at 350 nm in the difference spectra of iron(III) before and after the addition of glycerol, showing that iron(III) and glycerol form a 1 : 1 complex. Although the 13C NMR relaxation rates for all of the carbon atoms of glycerol and 1,3-propanediol were markedly affected by the addition of iron(III), the rate for C-2 of 1,4-butanediol remained unchanged. These facts indicate that either 1,2- or 1,3-diol, as didentate ligand, coordinates to a hydrolyzed iron(III) ion at acidic pH. In all of the present systems of iron(III) and polyols, iron(III) hydroxide-like precipitates resulted at around neutral pH. The polyols were removed in some quantities from solutions by adsorption on the precipitates; the removability depended on their molecular structures. In these polyols, only glycerol, which has three neighboring OH groups, formed soluble complexes at pH > 9 if R > 20. Accordingly, three neighboring OH groups seemed to be essential in the formation of soluble complexes at alkaline pH. In conclusion, the interaction between iron(III) and polyols are severely dependent upon the molecular structures of the polyols.