Nobukazu Okazaki

The oxygen exchange reaction of pentaamminechromatocobalt(III) ions with water

Abstract The oxygen exchange reaction of pentaamminechromatocobalt(III) ions with water in the presence of the concurrent hydrolysis of the complex ions has been studied at 0 and 25 °C in the pH-range 6.0–8.0. The results were interpreted by a set of concurrent mechanisms: 1) RHCrO2+4 + RCrO+4 ⇌ RCr2O7R4+ + OH−, 2) RHCrO2+4 + HCrO−4 ⇌ RCr2O+7 + H2O, 3) RCrO+4 + HCrO−4 ⇌ RCr2O−7 + OH−, and 4) RCrO+4 + H2O → ROH2+ + HCrO−4, HCrO−4 + H182O ⇌ HCrO183O− + H2O, ROH2+ + HCrO183O− → RCrO183O+ + H2O (R stands for (NH3)5Co·). The CrO bond is broken in the hydrolysis of the chromato complex at pH 6.7.

The kinetics of the hydrolysis reaction of pentaamminechromatocobalt(III) chloride

Abstract The hydrolysis reaction of pentaamminechromatocobalt(III) complex and the anation of the aqua complex by chromate ions: were studied at 25 °C, and in the pH ranges 6.0–8.5 and 3.5–7.5, respectively. The equilibrium constant of the hydrolysis reaction has a minimum value at pH ∼ 6. The important paths for the reaction (1) are: the rate constants were obtained as: k 1 = 2.2 × 10 −3 s −1 , k −1 = 2.3 M −1 s −1 , k 0 = 151 M −1 s − , and k −0 = 1.7 × 10 5 M −2 s −1 .