Promotion of the fenton reaction by Cu2+ ions: Evidence for intermediates

The promotion of the Fenton reaction by Cu2+ ions has been investigated using a wide range of [Cu2+]. Both the disappearance of Fe2+ and the evolution of O2 were followed as a function of time by quenching the reaction mixture with o‐phenanthroline or with excess Fe2 + ions, respectively. Two series of experiments were performed. In one series [H2O2] was 5 × 10−4 mol dm−3, and in the other [H2O2] was reduced to 5 × 10−5 mol dm −3. By stopping the reaction with excess Fe2+ ions, significant differences in the measured absorbance in the two series were observed. In the higher [H2O2] range, the absorbance decreased monotonically in time, due to O2 formation during the reaction. In the lower range, an initial transient rise of the absorbance was observed, indicating the formation of spectroscopically distinct intermediates in the system. A mechanism involving the intermediates FeOCu4+ and FeOCu5+ has been set up. Rate constants of the mechanism have been determined.