Mechanism of the acid catalysed hydrolysis of the chromatopenta-amminecobalt(III) ion

The kinetics of the acid hydrolysis of chromatopenta-amminecobalt(III) ion has been studied using a stopped-flow method over the acidity range 0.01≤[H⁺]<-1.0 mol dm⁻³ and 20.0°C<-ϕ<-30.0°C at ionic strengths 0.5 and 1.0 mol dm⁻³ (LiNO₃). These studies reveal that the complex is first protonated and subsequently hydrolysed to the aquapentaammine cobalt(III) ion. The rate constants for the hydrolysis of the mono and diprotonated species at 25°C are 0.83±0.01 s⁻¹ and (1.60±0.02)×10⁴ mol⁻¹ dm⁻³ s⁻¹, respectively. TMC 2664