Kinetics and Mechanisms of the Copper(II)-Catalyzed Oxidation of Iodide Ion in the Presence of Molecular Oxygen in Aqueous Acid Media.

Traces of copper(II) ion in 10−7—10−5 M (M = mol dm−3) catalytically accelerated the oxidation reactions of iodide ion to iodine in relatively strong acid solutions (pH ≤ 2) in the presence of molecular oxygen under conditions containing relatively high concentrations of I−. When a copper(II) solution was mixed with an iodide solution, after a rapid formation of iodine, it gradually increased according to the reaction times. For about 5 min after mixing, plots of [I3−]formed vs. t showed a good straight line; the formation rate of I2 (or I3−) increased proportionally with increasing concentrations of copper(II) ion and oxygen, with increasing concentrations of hydrogen ion and iodide ion, and with increasing temperature and with decreasing the ionic strength in the reaction solution. The formation rate of I2 was extremely inhibited by the presence of either radical scavengers or ethylenediaminetetraacetic acid (EDTA). A chain mechanism is presented to account for the obtained results.