Reduction of tris(2,2’-bipyridine)cobalt(III) complex by thiosulphate ion in an aqueous acidic medium

The reduction of tris(2,2-bipyridine)cobalt(III) complex by thiosulphate ion in an aqueous acidic medium gave a notable outcome. The stoichiometric evaluation indicates that one mole of the reducing agent has been consumed by one mole of the oxidant, and the reaction complies with an overall equation: 2[Co(bpy) 3 ] 3+ + 2S 2 O 3 2− 2[Co(bpy) 3 ] 2+ + S 4 O 6 2− The kinetics study conducted under a pseudo-first-order method shows that the rate of the reaction was acid-reliant and third-order overall; zero-order in the [oxidant], second-order in the [reductant], and first-order in the hydrogen ion concentration. The empirical rate expression complies with the equation:− [Co(bpy) 3 3+ ] = a [H + ][S 2 O 3 2− ] 2 ‘a’ = 77.82 dm 6 mol −2 s −1 ; at [H + ] = 2.0 × 10 −2 mol dm −3 , µ = 0.4 mol dm −3 (NaCl), T = 28 ± 1˚C and λ max = 560 nm.With increased ionic strength and decreased medium dielectric constant, the reaction rate increased. The inclusion of cations and anions accelerate and constricted the reaction rates respectively. Spectroscopic examination and kinetic evidence indicate an outer sphere mechanism, and the mechanism was therefore proposed via an outer-sphere route.