Vladislav Holba

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

Abstract The aquation kinetics of cis -[CoNH 3 Br(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 SUBSTITUTION OF NICOTINAMIDE AT PENTACYANO(NICOTINAMIDE)IRON(II) BY DIMETHYL SULFOXIDE IN AQUEOUS AND NON-AQUEOUS SOLVENTS

Abstract The effect of organic cosolvent on the rate constant and activation parameters δH‡, δS‡ of substitution of nicotinamide at pentacyano(nicotinamide)iron(II) by dimethyl sulfoxide was investigated in mixtures containing up to 50% methanol, t-butanol, acetone, acetonitrile, glycerine and glycol. From correlations between the logarithm of the rate constant and Grunwald-Winstein Y values, and between δ m δG‡ and excess Gibbs free energy of mixing GE, the effect of the change in the solvation on the reaction rate was elucidated. The effects of pH on the reaction rate and activation parameters, and the effect of organic cosolvent on the shift of the charge-transfer band of the complex mentioned above are also reported.

Kinetics of oxidation of pentaammine-isothiocyanato-cobalt(III) ion with peroxodisulphate and periodate in water and water-organic mixtures

SummaryThe kinetics of oxidation of [Co(NH3)5(NCS)]2+ by peroxodisulphate and periodate were investigated at different ionic strengths, and at different temperatures and concentrations of perchloric acid. Rate constants and activation parameters are also reported in mixed water-organic solvents. It was shown that the acid-base equilibria involving S2O8−2, and IO4− ions are important in the reactions studied. Solvent effects on the oxidation are interpreted in terms of the solvation of both the initial state and the activated complex.

Solvent Effect on the Kinetics of Oxidation of [Co(en)2SCH2CH2 NH2]2+ by S2O8 2−

The effect of the solvent on rate of the oxidation of [Co(en)2SCH2CH2NH2]2+ by S2O82− in aqueous mixtures of methanol (MeOH), tert-butyl alcohol (ButOH), acetonitrile (AN), ethylene glycol (EG) and ethylene carbonate (EC) has been analysed as regards initial and transition state contributions. From kinetic measurements and solubilities of the reactants, the Gibbs transfer functions, ΔGt°, corresponding to transfer of reactants and activated complex from water to water-organic mixtures were evaluated. The trends of the transfer functions are discussed in terms of ion-solvent interactions and the structural effects in the solvent mixtures.

Medium effect in the base hydrolysis of pentaamminebromocobalt(III) ion

SummaryThe effect of organic cosolvent on the rate constant of the base hydrolysis of pentaamminebromocobalt(III) ion was investigated in mixtures of H2O with MeOH, EtOH,i-PrOH,t-BuOH, and dioxane. The thermodynamic transfer functions, corresponding to the transfer of reactants and activated complex from water to the solvent mixtures, were evaluated from kinetic measurements and from solubilities of the complex salt. The experimental results are in good agreement with a dissociative mechanismvia the conjugate base.

Salt and medium effects in the aquation ofcis-amminebromobis(ethylenediamine)cobalt(III) ion

SummaryThe aquation kinetics ofcis-[Co(NH3)Br(en)2]2+ were studied in aqueous and mixed aqueous-nonaqueous solvents in the presence of KBr, KCl, LiCl, NaNO3 and NaClO4 as supporting electrolytes. It was found that the association between the complex ion and Cl−, Br− and NO3− ions takes place. The association constants, KIP, were evaluated from kinetic measurements. The kinetic parameters in the studied media are related to the influence of the cosolvents on the solvation spheres of the reactants and activated complex.

Solubility and thermodynamic transfer functions of hexa-amminecobalt(III) and tris(ethylenediamine)cobalt(III) hexacyanoferrates(III)

Abstract The solubilities of hexaamminecobalt(III) and tris(ethylenediamine) cobalt(III)hexacyanoferrates(III) were measured in water as well as in binary mixtures of water with tert -butyl alcohol and acetonitrile as a function of temperature. The Gibbs energies, enthalpies and entropies of transfer have been evaluated from experimental data. The contribution of [Co(NH 3 ) 6 ] 3+ , [Co(en) 3 ] 3+ and [Fe(CN) 6 ] 3− ions to the Gibbs energies of transfer of the investigated salts have been calculated using the TATB reference electrolyte assumption.

Enthalpies of transfer of monomethyl esters of dicarboxylic acids from water to aqueous-alcoholic solvent mixtures

Abstract Enthalpies of transfer of sodium salts of monomethyl esters of oxalic, malonic, succinic, adipic, fumaric, maleic, o -phthalic, isophthalic, and terephthalic acids from water to water-methanol and water- tert -butyl alcohol mixtures have been determined by calorimetry. Using literature data for the enthalpies of transfer for the sodium ion, based on extra thermodynamic TATB and TPTB assumptions, the enthalpies of transfer of the monoester anions were calculated. The results are discussed in terms of ion-solvent and solvent-solvent interactions.

Solvent effect on the initial state and transition state of anation of pentaammine-aquachromium(III) ion by thiocyanate

SummarySolvent effects on rate constants and activation enthalpies and entropies for the anation of [Cr(NH3)5H2O]2+ by SCN- in aqueous mixtures of MeOH, EtOH, i-PrOH and t-BuOH were analysed into initial and transition state contributions. From kinetic measurements, solubilities of the complex salt and enthalpies of solution, the thermodynamic transfer functions ΔGinftsupo, ΔHinftsupoand ΔSinftsupo, corresponding to the transfer of reactants and activated complex from water to aqueous-organic mixtures, were evaluated. The very small difference in solvation of initial and transition states, indicated by the analysis, seemed to be consistent with the proposed interchange mechanism.

Kinetics of oxidation ofcis-, andtrans-chlorobis(ethylenediamine)isothiocyanatocobalt(III)ion with peroxodisulphate in aqueous alcoholic mixtures

SummaryThe effect of organic cosolvent on the rate constants and activation parameters of oxidation of coordinativelybound thiocyanate with peroxodisulphate was investigated in mixtures of water with methanol,i-propanol andt-butanol. The thermodynamic transfer functions, corresponding to the transfer of reactants and activated complex from water to the solvent mixtures were evaluated from kinetic measurements and from the solubilities of corresponding salts. The experimental results are interpreted in terms of the solvation of both the initial state and the activated complex.