KINETICS AND MECHANISM OF THE COMPLEX-FORMATION OF THE CHLORITE ION AND IRON(III) IN AQUEOUS-SOLUTION

On the basis of rapid-scan spectrophotometric and one-wavelength stopped-flow experiments, the formation of the FeClO2(2+) complex was confirmed in the iron(III)-chlorite ion system. The complex formation is associated with the appearance of a new charge-transfer band in the visible spectral region. The stability constant of FeClO2(2+) was calculated from the final absorbance value of stopped-flow traces recorded at 510 nm. log K = 1.14 +/- 0.02 and epsilon-510 = 636 +/- 10 M-1 cm-1 (I = 1.0 M (NaClO4), 25-degrees-C). It was demonstrated that the complex formation is kinetically coupled with catalytic decomposition of ClO2-. The proposed mechanism for the ligand substitution reaction includes the reactions of Fe3+ and Fe(OH)2+ and also a generalized pathway for the chlorite ion decomposition. The rate constant for the Fe3+ + ClO2- = FeClO2(2+) step, 269 +/- 55 M-1 s-1, is consistent with an associative interchange mechanism predicted by previous kinetic data for complex formation reactions of Fe(III).