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Effects of solvent on the reactions of coordination complexes: Part 17. Kinetics and mechanism of base hydrolysis of (αβS) (salicylato) (tetraethylenepentamine)cobalt (III) in methanol + water and dimethylsulphoxide + water media
Author(s) -
Dash Anadi C.,
Das Prafulla K.
Publication year - 1992
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.550240205
Subject(s) - chemistry , hydrolysis , solvation , solvent , solvent effects , cobalt , catalysis , base (topology) , kinetics , medicinal chemistry , methanol , inorganic chemistry , organic chemistry , mathematical analysis , physics , mathematics , quantum mechanics
The base hydrolysis of (αβS) (salicylato) (tetraethylenepentamine)cobalt(III) has been investigated in MeOH + water and DMSO + water media (0–70% (v/v) cosolvents) at 20.0 ⩽ t °C ⩽ 35.0 and I = 0.10 mol dm −3 (ClO 4 − ). The phenoxide species [(tetren)CoO 2 CC 6 H 4 O] + undergoes both OH − ‐independent and OH − ‐catalyzed hydrolysis via SN 1 ICB and SN 1 CB mechanism, respectively. The OH − ‐independent hydrolysis of the phenoxide species is catalyzed by both DMSO + water and MeOH + water media, the former exerting a much stronger rate accelerating effect than the latter. The OH − ‐catalyzed reaction is strongly accelerated by DMSO + water medium but insensitive to the composition of MeOH + water medium up to 40% (v/v) MeOH beyond which it was not detectable under the experimental conditions. Data analysis has been attempted on the basis of the solvent stabilizing and destabilizing effects on the initial state and transition state of the concerned reactions. The nonlinear variation of the activation parameters, Δ H ≠ and Δ S ≠ , with solvent compositions presumably indicates that the solvent structural effects mediate the energetics of solvation of the initial state and transition state of the concerned reactions. The linearity in Δ H ≠ vs. Δ S ≠ plot accomodating all data for k 1 and k 2 paths in DMSO + water and MeOH + water further suggests that the solvent effects on these parameters are mutually compensatory.