A kinetic investigation of the reaction of ethylenedinitrilotetraacetic acid (EDTA) and cerium (IV) in acid solution

The reaction between Ce(IV) salt solutions and EDTA solution was followed titrimetrically and spectrophotometrically and found to occur in stages. Four equivalents of Ce(IV) are reduced per mole of EDTA almost instantaneously at room temperature or even lower. With increasing temperature and reaction time an ultimate of about 14 equivalents of Ce(IV) is consumer per mole of EDTA. Formaldehyde, carbon dioxide, and other unidentified compounds are the products of oxidation of EDTA with Ce(IV). The kinetics of the reaction in aqueous sulfuric acid (0.09 - 2.95 M̲) was studied over the temperature range 11.7-40⁰ by a spectrophotometric technique. In the region of concentrations workable in UV spectrophotometry (10⁻⁵ -- 10⁻⁴ M̲ Ce(IV)), and where one mole of EDTA reduced four moles of Ce(IV), the reaction is first order in each reactant and shows variable dependence on the concentration of hydrogen ions. The reaction rate is a maximum at about 1 M̲ [H⁺] and decreases on either side. Only below unit molar concentration of H⁺ a Ce(IV)-EDTA complex is observed to form and decay --Abstract, page ii