The N-hydroxyethylethylenediaminetriacetic Acid-iron-ascorbic Acid Complex

Résumé du livre

N-hydroxyethylethylenediaminetriacetic acid (HEDTA) forms a 1:1 complex with Fe(II). The number of carboxylate groups bonded to iron is heavily influenced by pH and all three groups become attached to iron at pH 6.5. Ascorbic acid reacts with Fe(II) and forms complexes whose color depend on the pH of the solution. Upon addition of ascorbic acid, ferric ions are immediately reduced to ferrous ions. Addition of ascorbic acid to the HEDTA-Fe(II) solution causes the development of a purple color due to the formation of a new mixed ligand complex, the HEDTA-Fe(II)-Asc. Ac. complex. This paper reports the preparation of the HEDTA-Fe(II)-Asc. Ac. complex, its composition, and its possible structure. The optimum pH for the formation of the purple complex was found to be 4. The aqueous complex solution is very unstable; the purple color of the solution fades rapidly with time. The color fades under both nitrogen or oxygen atmosphere. However, the purple complex solution is more stable under a nitrogen atmosphere than under an oxygen one. Organic solvents stabilize the purple aqueous complex solution. Glycerol also stabilizes the solution, but its stabilizing effect is larger than that of the organic solvents especially under a nitrogen atmosphere. The formation of the new mixed ligand complex, HEDTA-Fe(II)-Asc. Ac. is a highly specific reaction for both iron and ascorbic acid. Also the reaction takes place only in the presence of aminotricarboxylic acids, namely NTA, HEDTA, and TTHA (which may be considered as two aminotricarboxylic acids joined by an ethylene group). It offers a qualitative test for iron and ascorbic acid. It has potential to develop quantitative methods for determining iron and ascorbic acid.