Kinetics of aquation ofcis- andtrans-chloro-nitrobis-(ethylene-diamine)cobalt(III) ion in binary aqueous mixtures

Kinetics of aquation ofcis- andtrans-[Co(en)₂NO₂Cl]⁺ were investigated in aqueous mixtures of MeOH, EtOH,i-PrOH andt-BuOH at 298.1 K. The values of transfer functions corresponding to the transfer of reactant and activated complex from H₂O to the solvent mixtures were calculated from kinetic measurements and from solubilities of the complex salt. The results of the analysis of solvent effect are discussed in terms of D and I_d mechanisms. TMC 2676     

Kinetics and mechanism of substitution of aqua ligands fromcis-diaqua-bis(bipyridyl ruthenium(II)) complex by salicylhydroxamic acid in aqueous medium

The kinetics of substitution of aqua ligands fromcis-[Ru(bipy)₂(H₂O)₂]²⁺ ion by salicylhydroxamic acid (L) in aqueous medium has been studied spectrophotometrically at different temperatures (50–65°C). The following rate law has been established in the pH range 4.0 to 5.8;

Kinetics of substitution of aquo ligands fromcis-diaquo-bis-(biguanide) cobalt(III) and chromium(III) ions by aspartic acid in ethanol—water mixtures

The kinetics of substitution of aqua ligands fromcis-diaqua-bis(biguanide)cobalt(III) and chromium(III) ions by aspartic acid in EtOH–H₂O media have been studied spectrophotometrically in the 30 to 45°C range. We propose the following rate law for the anation

Substitution of aqua ligands fromcis-diaqua-bis(bipyridyl) ruthenium(II) by 1, 10-phenanthroline in aqueous medium

The kinetics of aqua ligand substitution fromcis-[Ru(bipy)₂(H₂O)₂]²⁺ by 1, 10-phenanthroline (phen) have been studied spectrophotometrically in the 35 to 50°C temperature range. We propose the following rate law for the reaction within the 3.65 to 5.5 pH range:

Kinetics of substitution in two water soluble cobalt(III)-porphyrins

Summary Kinetics of substitution of thiocyanate and pyridine in the axial positions of tetra(p-trimethylammoniumphenyl)porphinatocobalt(III) and tetra(p-sulfonatophenyl)porphinato cobalt(III) were investigated at pH 4.00 and ionic strength 0.1 M (NaNO₃) in aqueous solution. These reactions were found to be as facile as other such reactions of cobalt(III) porphyrins even though a new synthesis was employed in the present study. The rates of these reactions are proportional to the base strength of the parent free base porphyrin. Electrostatic attraction between the ligand and the porphyrin peripheral charges were also found to enhance the rates. The cause of labilization is believed to be primarily electronic and not steric.     

Kinetics of substitution of aqua ligands from cis-diaqua(ethylenediamine)platinum(II) perchlorate by DL-penicillamine in aqueous medium

The kinetics of the interaction of DL-penicillamine with [Pt(en)(H₂O)₂]²⁺ have been studied spectrophotometrically as a function of [Pt(en)(H₂O)₂]²⁺, [DL-penicillamine] and temperature at pH 4.0. The reaction proceeds via rapid outer sphere association complex formation, followed by two slow consecutive steps. The first is the conversion of the aforementioned complex into the inner sphere complex and the second is the slower chelation step whereby another aqua ligand is replaced. The association equilibrium constant (K _E) for the outer sphere complex formation has been evaluated together with rate constants for the two subsequent steps. Activation parameters have been calculated for both steps using the Eyring equation (H ₁ = 46.5 ± 5.0 kJ mol^–1, S ₁ = – 143.0 ± 15.0 J K^–1 mol^–1, H ₂ = 44.3 ± 1.3 kJ mol^–1, S ₂ = –189.0 ± 4.2 J K^–1 mol^–1). The low enthalpy of activation and large negative entropy of activation values indicate an associative mode of activation for both aqua ligand substitution processes.     

Kinetics and mechanism of the displacement of aqua ligands from cis-diaqua-bis(biguanide)chromium(III) by pyridine-2-aldoxime in EtOH-H2O mixtures

Kinetic and mechanistic studies of the displacement of aqua ligands from cis-[Cr(BigH)₂(H₂O)₂]³⁺ (BigH = H₂NC(NH)CHC(NH)NH₂) by pyridine-2-aldoxime (LH) in EtOH-H₂O mixtures, in the 30–45° C range, obey the following rate law over the 3.5–6.0 pH range,

Kinetics of the solvolysis of the cis-chloroazidobis-(1,2-diaminoethane)cobalt(III) ion in water+t-butanol mixtures

Summary Rate constants for the solvolysis of the complex ioncis-[Coen₂N₃Cl]⁺ have been determined for a range of temperatures in mixtures of water witht-butanol ranging up to 50% v/v of the latter. Linear plots of log (rate constant) against the reciprocal of the absolute temperature are obtained at all concentrations oft-butanol and the variations of the enthalpy and entropy of activation with solvent composition show extrema at compositions where extrema occur in the physical properties of the mixture which are influenced by solvent structure. The importance of solvent structure is shown by the curved plot found for log (rate constant) against reciprocal of dielectric constant at constant temperature. The application of a free energy cycle to the free energies of activation in water and in the mixture and the free energies of transfer of individual ionic species between water and the mixtures shows that the effect of changes in solvent structure on the reacting cation in the transition state dominates over that in the initial state.     

Kinetics of substitution on chloro-1,1,7,7-tetraethyldiethylene-triaminegold(III) in methanol-water mixtures

Summary Rate constants are reported for the replacement of chloride by bromide in the complex [Au(Et₄dien-H)⁺ in methanol-water mixtures. This reaction follows the usual two-term rate law = (k_obs = k₁ + K₂[Br^–1]) for square planar complexes in all the mixtures studied. The logarithms of the rate constants correlate with Grunwald-Winstein solvent Y values and yield slopes of 0.32 (k₁) and 0.15 (k₂). The results suggest that both reaction paths are associative.Dien complexes of gold(III) yield conjugate base species at low pH; Et₄dien-H = Et₂NCH₂CH₂NCH₂CH₂NEt₂.     

Kinetics of aquation of pentaammine(substituted salicylato)cobalt(III) complexes by ferric ion

Summary The aquation of pentaammine (substituted salicylato) cobalt(III) complexes [(NH₃)₅CoO₂CC₆H₃(X)OH]²⁺,X = 5-SO₃, 5-Br, 5-NO₂, and 3-NO₂ in the presence of ferric ion was studied spectrophotometrically in the 65°–80° range. Ferric ion catalyses the aquation of the substratesvia formation of a reactive binuclear species.Reprints of this article are not available.     

Thermodynamics of dissolution of chromium(III) and cobalt(III) trisacetylacetonates in water-ethanol solvents

The study presents solubility data for chromium(III) and cobalt(III) trisacetylacetonates in water-ethanol solvents over a wide range of temperatures and ethanol concentrations. The solubilities of both compounds increase as the temperature or ethanol concentration is raised, particularly in the case of Cr(acac)₃ it increases to a greater extent. Noteworthy, for ethanol concentrations of 1.4–1.6 mol/L tinversion of the temperature effect on the solubilities of both compounds is observed. For ethanol concentrations lower than 1.4–1.6 mol/L, dissolution of Cr(acac)₃ and Co(acac)₃ is exothermic, whereas for the higher concentrations, it is endothermic. The changes in enthalpy and entropy upon dissolution of the compounds under study were evaluated using the temperature dependence of solubility.     

Kinetics and mechanism of dissociation of oxalatobis(phenanthroline)cobalt(III) ion in aqueous hydrochloric acid media

The kinetics of dissociation of oxalatobis(phenanthroline)cobalt(III) ion into cis-diaquobis(phenanthroline)cobalt(III) ion in aqueous HClKCl media have been studied. The rate is first-order with respect to acid concentration (1–2 M) with a specific rate constant, k_H = 6.2 × 10⁻⁴M⁻¹min⁻¹ at 75°C (μ, 2 M); ΔH^≠ and ΔS^≠ values are 22.1 kcal mole⁻¹ and −18.7 e.u., respectively. The magnitude of the ΔS^≠ value appears consistent with a dissociation mechanism involving reaction of the conjugate acid form of the complex (S_N 1CA mechanism).     

Kinetics and mechanisms of substitution of aqua ligands from cis-diaquo-bis[2-(m-tolylazo)pyridine]ruthenium(II) by 8-hydroxy- quinoline in ethanol—water mixtures

Transition Metal Chemistry - The kinetics of aqua ligand substitution from cis-[Ru-(tap)2(H2O)2]2+ (tap = 2-[m-tolylazo]pyridine) by 8-hydroxyquinoline (oxine) have been studied...     

Kinetics of the oxidation of diaqua(nitrilotriacetato)cobaltate(II) in water-ethanol mixtures

Summary The kinetics of the oxidation of diaqua(nitrilotriacetato) cobaltate(II) by periodate have been studied in various ethanol-water mixtures covering the range 0 to 65 wt% ethanol, at seven different temperatures in the range 20–50 °C. The effect of solvent on the rate and mechanism of the reaction has been investigated. An inner-sphere mechanism for the reaction is proposed, a result consistent with the calculated activation parameters.     

The kinetics of aquation of cis-ammine-bromobis(ethylenediamine) cobalt(III) ion in water-organic mixtures

The aquation kinetics of cis-[CoNH₃Br(en)₂]²⁺ were investigated in aqueous mixtures of ethyl alcohol, isopropyl alcohol, t-butylalcohol and acetonitrile. The rate constants, activation enthalpies and entropies were determined. The interpretation of the experimental data, based on electrostatic theory, was possible only when methyl alcohol and ethyl alcohol were used as co-solvents. It was shown that in the mechanism of reaction studied non-electrostatic interactions play an important role.     

Kinetics of aquation of cis- and trans-chloro-nitrobis(ethylenediamine) cobalt(III) ion in aqueous mixtures of ethylene carbonate and propylene carbonate

Summary The kinetics of aquation of cis- and trans-[Co(en)₂-NO ₂Cl] ⁺ were investigated in quasi-isodielectric aqueous mixtures of ethylene carbonate (EC) and propylene carbonate (PC) over a range of temperatures. Transfer Gibbs energies of reactant and transition state from H₂O to aqueous mixtures of EC were evaluated from kinetic measurements and the solubilities of the complex salt. An analysis of the solvent effect on the solvation of the initial (IS) and transition (TS) state reveals that their stabilization by non-aqueous cosolvent is due to predominant ion-dipole and dispersion interactions.