Promotion of the fenton reaction by Cu 2+ ions: Evidence for intermediates

The promotion of the Fenton reaction by Cu 2+ ions has been investigated using a wide range of [Cu 2+ ]. Both the disappearance of Fe 2+ and the evolution of O 2 were followed as a function of time by quenching the reaction mixture with o ‐phenanthroline or with excess Fe 2 + ions, respectively. Two series of experiments were performed. In one series [H 2 O 2 ] was 5 × 10 −4 mol dm −3 , and in the other [H 2 O 2 ] was reduced to 5 × 10 −5 mol dm −3 . By stopping the reaction with excess Fe 2+ ions, significant differences in the measured absorbance in the two series were observed. In the higher [H 2 O 2 ] range, the absorbance decreased monotonically in time, due to O 2 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 FeOCu 4+ and FeOCu 5+ has been set up. Rate constants of the mechanism have been determined. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 725–736, 2006