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

Abstract

The kinetics of aquation and base hydrolysis reactions of fmns-[Co(NH 3 ) 4 (NH 2 CH 3 )(OSO 3 )] + have been studied. In acid solution the aquation rate, R aq , follows the equation R aq /[complex] = k s + k c [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 k s = 4.15 χ 10 -6 s -1 and k c = 4.52M -1 s -1 . The rate of base hydrolysis, R OH , follows the equation R OH/ complex] = k 0H [OH - ]. The activation parameters are ΔΗ* OH =74.9kJmol -1 and ΔS* OH = 2JK -1 mol -1 and the rate constant is k OH = 0.58M 1 s -1 at 25°C and μ, = 0.15 Μ. The stereochemistry of the hidroxo product has been determined (cis-[Co(NH 3 ) 4 (NH 2 CH 3 )- (OH)] 2+ =9%). The results are discussed in the light of the reaction mechanisms proposed so far.