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Kinetics of the solvolysis of [Co(3Rpy) 4 Cl 2 ] + (R = Me or Et) in water + propan‐2‐ol mixtures
Author(s) -
Elsubruiti Gehan M.,
Wells Cecil F.,
Sidahmed Ibrahim M.
Publication year - 1991
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.550230207
Subject(s) - chemistry , solvolysis , solvent , ion , methanol , chloride , analytical chemistry (journal) , inorganic chemistry , hydrolysis , organic chemistry
Rates of solvolysis of complex ions [Co(3Rpy) 4 Cl 2 ] + with R = Me and Et have been determined in mixtures of water with the hydrophobic co‐solvent propan‐;2‐ol for a range of temperatures. The variations of the enthalpies and entropies of activation with the solvent composition have been correlated with the physical properties of the solvent and it has been shown that the linear plot found for Δ H * against Δ S * in water + propan‐2‐ol is coincident with that found for water + methanol mixtures. A free energy cycle has been applied to the dissociative‐type process of initial state (C n + ) going to the transition state (M ( n +1)+ …‥ Cl − ) using values for the free energy of transfer of the chloride ion from water into the mixture, Δ G t ∘(Cl − ), derived from the solvent sorting technique or from the TATB/TPTB method. Irrespective of the source of Δ G t ∘(Cl − ), it is found that Δ G t ∘(Co(3Rpy) 4 Cl 2+* ) ca. Δ G t ∘(Co(3Rpy) 4 Cl 2 + ) (where * indicates a species in the transition state) for mol fractions of propan‐2‐ol x 2 ≳ 0.04–0.05 with Δ G t ∘(Co(3Rpy) 4 Cl 2+* ) becoming increasingly more negative than Δ G t ∘(Co(3Rpy) 4 Cl 2 + ) as x 2 increases above 0.05. These variations are compared with those for the solvolysis of the same ions in water + methanol mixtures and of a range of other ions in water + propan‐2‐ol mixtures. It is concluded that, using values for Δ G t ∘(Cl − ) from either source, the stabilizing influence of changes in solvent structure is greater on the cation in the transition state than on the cation in the initial state for the solvolyses of complexes [Co(Rpy) 4 Cl 2 + ] and [Coen 2 LCl] n + .