Aquation and Base Hydrolysis of trans-Tetraammine(methylamine)sulfatocobalt(III) Complex Ion

Abstract The kinetics of aquation and base hydrolysis reactions of fmns-[Co(NH3)4(NH2CH3)(OSO3)]+ have been studied. In acid solution the aquation rate, Raq, follows the equation Raq/[complex] = ks + kc[H+], at constant ionic strenght μ = 1.0Μ. The activation parameters are ΔΗ* = 88.8 kj mol-1, ΔS* = - 50.5 JK-1 mol-1 , ΔΗ* = 96.7 kj mol-1 and ΔS* =-23 JK-1 mol-1. The rate constants at 25°C are ks = 4.15 χ 10-6s-1 and kc = 4.52M -1s-1 . The rate of base hydrolysis, ROH, follows the equation ROH/complex] = k0H [OH-]. The activation parameters are ΔΗ*OH =74.9kJmol-1 and ΔS*OH = 2JK-1 mol-1 and the rate constant is kOH = 0.58M 1 s-1 at 25°C and μ, = 0.15 Μ. The stereochemistry of the hidroxo product has been determined (cis-[Co(NH3)4(NH2CH3)- (OH)]2+ =9%). The results are discussed in the light of the reaction mechanisms proposed so far.