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|Title:||Acid catalysis and nitrate ion effect on aquation of maleato- and fumarato-pentaamminecobalt (III) complexes|
|Abstract:||The kinetics of dissociation of maleate and fumarate from the maleato- and fumarato-pen taamminecobait (III) complexes have been investigated in aqueous perchloric acid (0.1 to0.7 mol dm-3) over a temperature range of 60-80°C at an ionic strength of 1.0 mol dm-3 adjusted with sodium perchlorate. Variation of observed pseudo first order rate constants on [acid] suggests operation of two concurrent path with kobs = k1 + k2 [H +], where k1 and k2 are the rate constants for the uncatalysed and acid-catalysed pathways respectively. Under identical conditions, fumaratopentaamminecobalt (III) complex is more reactive than maleatopentaamminecobalt (III) complex. The influence of free carboxylic proton and nitrate ion effect on the rate of substitution reactions have been discussed. Analysis of the rate data corresponding to k2suggests a dissociative mechanism involving the protonated species (protonation on the adjacent carbonyl oxygen and not on the carboxylate oxygen). The solvent isotope effect, kD2O/kH2O for the dissociation process is 2.6, consistent with a mechanism involving a rapid pre-equilibrium protonation step followed by a slow rate-determining dissociation. Mechanisms involving concerted attack by H+ and H2O are excluded.|
|Appears in Collections:||IJC-A Vol.30A(12) [December 1991]|
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