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Kinetics of the solvolysis of the trans-dichlorobis(1,2-diaminoethane)-cobalt(III) Ion in water + urea mixtures

✍ Scribed by Grahame S. Groves; Cecil F. Wells

Publisher: John Wiley and Sons
Year: 1986
Tongue: English
Weight: 392 KB
Volume: 18
Category: Article
ISSN: 0538-8066
DOI: 10.1002/kin.550180503

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✦ Synopsis

Following the kinetic investigation of the solvolysis of a range of cobalt(II1) complexes in mixtures of water + cosolvent where the cosolvent enhances the solvent structure and decreases the dielectric constant, kinetic data are now reported for such a solvolysis in water + urea where urea acts as a structure breaker and enhances the dielectric constant. A plot of log (rate constant) against reciprocal of the dielectric constant shows that differential effects of changes in solvent structure occur between the initial and the transition states and, as in the investigations using structure-enhancing cosolvents, the principal effect of change in solvent structure on the cobalt(II1) cation occurs on the penta-coordinated ion in the transition state.

The kinetics of the solvolysis of the trans-[Coen2C121f cation (en = 1,2-diaminoethane) have been investigated in water + propan-2-01 [ll, water + t-butyl alcohol [2J, and water + ethanonitrile [31 over a range of temperatures and solvent compositions. Whereas the first two cosolvents considerably enhance the structure of water when added in small concentrations and ethanonitrile has much less of an effect, all three cosolvents reduce E41 the dielectric constant when added to water. However, the linear plots for the variation of log (rate constant) against the reciprocal of the dielectric constant at constant temperature, expected [5-71 for the interaction of charges in a dielectric continuum, are not observed 11-31. For the extension of an MZM . . .Xzx bond in the transition state for the solvolysis of a metal complex C z C , the Laidler-Landskroener equation [51 extended [81 to allow for the effect of changes in solvent structure applies.

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