Study of the Complexes of the Ascorbic Acid-Iron(III) System

The structure of ascorbic acid has been widely studied [1] and was found to correspond to the enol of 3-keto-D-gulofuranolactone, i.e. it has a lactone structure with an endiol group. Biologically, the two acids, and in particular Lascorbic acid, are used to counteract scurvy. In pharmaceutics they are widely used [2, 3] and fulfill the function of an anti oxidizing agent in the food industry. Dehydroascorbic acid is formed through the oxidation of ascorbic acid. This reaction has been studied using various oxidizing ions such as Co(III)4, Cu(II) [5, 6], Ti ( III ) -H 2 0 2 [7] and Fe(III) [8], Recently, the same reaction has been studied with electrochemical techniques [9]. Likewise, a kinetic study has been carried out on the hydrolysis products of dehydroascorbic acid [10]. Laurence and Ellis [11] detected, with the stopped flow technique, a blue intermediate in the oxidation of L-ascorbic acids by Fe3+ ions. They obtained the absorption spectrum in the visible range of this intermediate with a point by point measurement of maximum values of optical densities (absorbances) at various wavelengths. At around X = 560 nm they found a wide band of maximum absorption and assumed that the intermediate was the ferric ascorbate complex AHFe+ + . These authors worked with a highly acid medium (H+ = 0.2 M, i.e. pH = 0.7). and therefore the blue intermediate was obtained in solution for only a short period of time. In the present paper, with a higher pH than that used by Laurence and Ellis the blue complex was