DIFFERENCE IN THE KINETIC-BEHAVIOR ON THE AC-CATALYZED DECOMPOSITION (AC EQUALS ACTIVATED CARBON) OF [CO(C2O4)(3)](3-) AND [CO(NH3)(5)(H2O)](3-CATALYZED LIGAND-SUBSTITUTION REACTIONS BETWEEN EACH COMPLEX AND EDTA IN AN AQUEOUS-SOLUTION(), AND ON THE AC)

The decomposition reaction of tris(oxalato)cobaltate(III) ion, [Co(ox) (3)](3-), occurred to produce cobalt(II) ion and carbon dioxide by add ing activated carbon (AC) in an aqueous solution, taking a rate law of the first order with respect to the concentrations of not only [Co(ox )(3)](3-), but also AC. The rate of decomposition was independent of t he pH values over a wide range of 2-8. On the contrary, the pentaammin eaquacobalt(III) ion, [Co(NH3)(5)(H2O)](3+), did not decompose at all under the same conditions. When the same reaction mixtures as mentione d above contained ethylenediaminetetraacetate (EDTA), which denotes al l forms of H(4)edta, H(3)edta(-), H(2)edta(2-) etc., both of the compl exes, [Co(ox)(3)](3-) and [Co(NH3)(5)(H2O)](3+) converted quantitative ly to [Co(edta)](-), taking a first-order rate law with respect to the concentration of either [Co(ox)(3)](3-) Or [Co(NH3)(5)(H2O)](3+) The rate was proportional to the added AC amounts, and was extremely inhib ited by adding 8-quinolinol (oxine), methanol, or ethanol. The pH depe ndence on the reaction rates was extremely different in [Co(ox)(3)](3- ) and [Co(NH3)(5)(H2O)](3+); the rate in the former case was independe nt of the pH in the 2-5, and decreased at less than 2 and at larger th an 5; that in the latter case was maximum at around pH 6, and decrease d accordingly to pH's less or larger than ca. 6, and became almost zer o at pH 2. Such differences in the kinetic behavior are discussed.