Determination of Redox Potential and Stability Constant of Iron(III)-3-Hydroxy-2-Methyl-4-Pyrone Complexes

Maltol (3-HYDROXY-2-METHYL-4-PYRONE) is a monobasic bidentate ligand for a number of metal ions. It forms a stable 5-membered chelate ring with the metal ions. Having a very low toxicity index it has found extensive use as a flavouring agent. Depending on the oxidation state of the metal ion and the metal to ligand stoichiometry, the complex ion can be uncharged or it may have a +1 or +2 charge. This study describes the results of a potentiometric study for the determination of stability constants and a spectrophotometric determination of pH dependent redox potential at pH 3.0, 4.0, 5.0 and 7.0 using ascorbate as a reducing agent. At 25o C, the results were: log b1 = 11.20, log b2 = 21.90 log b3 = 28.20 and Eo complex (vs NHE) at pH 3.0 = 0.229; pH 4.0 = 0.144; pH 5.0 = 0.107; pH 7.00 = 0.0442. These results are interpreted in terms of efficacy of maltol for its proposed usage for different medical applications.