The kinetics and mechanism of the iron(III)-catalyzed decomposition of the chlorite ion have been investigated by using conventional batch, stopped-flow, stopped-flow-rapid-scan spectrophotometric, and quenched stopped-flow methods at 25 °C and in 1.0 M NaClO4-. The concentration vs time profiles were determined for chlorite ion, chlorine dioxide, and, in a few cases, chloride ion in the 40 ms-several minute interval. It was confirmed that the stoichiometry can be given as the appropriate combination of the following reactions: 4HClO2 = 2ClO2 + ClO3- + Cl- + 2H+ + H2O; 5HClO2 = 4ClO2 + Cl- + H+ + 2H2O. The proposed mechanism postulates that the catalytic decomposition is initiated by the formation of the FeClO22+ complex and the rate-determining step is the redox decomposition of this species. The mechanism was validated by model calculations based on the GEAR algorithm. The measured and calculated kinetic curves are in excellent agreement under a variety of experimental conditions. It was shown that the overall stoichiometry is kinetically controlled and ultimately determined by fast secondary reactions between various chlorine species. This work represents the first totally inorganic application of the quenched stopped-flow method. Several aspects of this technique are discussed.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry