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http://nopr.niscpr.res.in/handle/123456789/15712| Title: | Effect of solvent on the reactions of coordination complexes: Part 25 - Kinetics of base hydrolysis of some (aminomonocarboxylato) (tetraethylenepentamine )cobalt(III) complexes in propan-2-ol + water, t-butanol + water, ethylene glycol + water & 2-methoxyethanol + water media: Delineation of preferential solvation & solvent structure on reactivity |
| Authors: | Dash, Anadi C. Das, Smrutiprava |
| Issue Date: | May-1999 |
| Publisher: | NISCAIR-CSIR, India |
| Abstract: | The base hydrolysis of [(tetren)CoO2 CR]2+ { R
= -CH2NH2, -CH2CH2NH2,
pyridine-2-( βS isomer); -CH(CH3)NH2 (βS and βR) isomers} have been investigated in aquo-organic
solvent media using propan -2-ol , t-butanol
, 2-methoxyethanol, and ethylene glycol as cosolvents at 20.0 ≤t/°C ≤40.0. These substrates undergo
substitution of the carboxylate ligands in basic medium via SN,CB mechanism.
Rate acceleration has been observed with increase in mole fraction ( Xorg) of the cosolvent
except for EG + H2O for
which there is a small rate retardation. The observed reactivity trend could be
interpreted in terms of the destabilisation of the Iyate ion, and preferential
solvation of the initial state and the transition state mediated by hydrophobic
interaction, and solvent structure. The preferential solvation is assessed in
terms of the parameter, δ = Xorg L- Xorg where Xorg L denotes the local mole fraction of
the cosolvent in the solvent cosphere of a substrate, Xorg being the same in the bulk phase. The Gibbs
excess free energy (GE) of the mixed solvent is taken to be an indicator
of solvent structure. The rate constants could be used to show that the
isomerisation reaction βR← βS for
the -alaninato complex in the transition state of base hydrolysis relative to
the same for the initial state is increasingly less favoured with increase in Xorg This process is mediated by hydrophobicity and
structure of the medium. The extrema in the plots of activation enthalpy versus
Xorg
support that solvent structure controlled the energetics of the reaction. A
linear correlation between ΔH‡
and ΔS‡ irrespective of solvents, solvent
compositions and substrates shows that the intimate mechanism is not perturbed
by the solvent effects. However, the sol vat ion components of ΔH‡ and
ΔS‡ are mutually
compensatory. |
| Page(s): | 434-445 |
| Appears in Collections: | IJC-A Vol.38A(05) [May 1999] |
Files in This Item:
| File | Description | Size | Format | |
|---|---|---|---|---|
| IJCA 38A(5) 434-445.pdf | 2.45 MB | Adobe PDF | View/Open |
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