Ernestina Muñoz

Kinetics of the oxidation of iodide by persulphate in AOT–oil–water microemulsions

The oxidation of iodide by persulphate has been studied in different sodium bis-2-ethylhexylsulphosuccinate (aerosol-OT or AOT)–oil–water microemulsions at 298 K. The rate of this reaction is appreciably higher in a microemulsion than when it takes place in a conventional aqueous medium. The dependence of the rate constant on the surfactant concentration as well as on the molar ratio R(=[H2O]/[AOT]) has been examined. The results are interpreted on the basis of the anionic nature of the reactants and the surfactant itself, and the high concentrations of sodium cations inside the aqueous cores. The dependence of the rate constant on the nature of the organic phase present in the system has also been investigated.

Salt effects on the kinetics of dissociation of the pentacyano-4-cyanopyridineferrate(II) anion

SummaryThe kinetics of replacement of 4-cyanopyridine (4-CNpy) by CN− in [Fe(CN)5(4-CNpy)]3− have been studied in different concentrations of electrolyte. Plots of ln (k/kw)versus (γ−γw), where the subscript w refers to pure water and γ is the surface tension of the appropriate salt solution, gave a common straight line for all the electrolytes studied. This result seems to confirm theD character of the process studied and permits an estimate of the activation volume to be made from kinetic data.

Solvent effects on substitution reactions at complexes of the [Fe(CN)5L]3- type in binary aqueous mixtures

SummaryThe kinetics of replacement of 4,4′-bipyridine, (4,4′-bipy), and 4-cyanopyridine, (4-CNpy), by cyanide in [Fe(CN)5-(4,4′-bipy)]3-. at 298 K have been studied in binary aqueous mixtures containing different amounts of t-butanol, methanol, glycerol, ethyleneglycol and sucrose. The plots of logarithms of the limiting rate constantsversus the mole fraction of water are linear over the entire composition range studied, showing the importance of solvation phenomena. A different straight line of log (kL/s−1)versus XH2O is obtained for each mixture, indicating the influence of other solvent parameters on the reaction rate. A multiparameter regression of δΔGexp≠ with A (acidity vector), B (basicity vector) and GE is used for both reactions; plots of δΔGcalc≠versus ΔΔGexp≠ are linear with slopes of near unity.

Kinetic salt effects in the bromide oxidation by bromate

The kinetic salt effect on the oxidation of bromide ion by bromate have been studied. It is concluded that the salt effects are the result of ion-solvent interactions and seem to be connected not only to the strength of these interactions, as measured by the lowering of solvent activity, but also by the structural characteristics of ion-solvent interactions. This conclusion is based on the use of Pitzers treatment to estimate the activity coefficients.

Volumes of activation for dissociation of pentacyanoferrates(II) through pressure and salt effects on reactivity

SummaryDependences of rate constants on pressure (up to 1 kbar) and on added salt concentration (up to 6.0 mol dm−3 LiNO3, NaNO3, NaCl, Na2SO4 or KNO3) have been established for dissociative substitution of pentacyanoferrates(II), [Fe(CN)5L]3− with L = 4-cyanopyridine, 4,4′-bipyridyl, 4-phenylpyridine and 4-t-butylpyridine. Activation volumes derived directly from pressure effects, and indirectly from salt effects via surface tension dependences and derived surfaces of activation, are reported, compared and discussed.

Kinetics of the oxidation of iodide by peroxodisulphate in reverse micelles

Abstract The kinetics of the oxidation of iodide by peroxodisulphate has been studied in the AOT/ n -heptane/water system (AOT = sodium bis(2-ethylhexyl) sulfosuccinate). The reaction rate is dependent on the number of reverse micelles present in this system. For a given number of these micelles, the rate of reaction increases as the water content of the reverse micelles decreases.

Kinetics of oxidation of iodide by hexacyanoferrate(II) in binary aqueous solvent mixtures

SummaryThe kinetics of the oxidation of iodide by hexacyanoferrate(III) have been studied in different H2O-methanol, t-butanol, ethylene glycol glycerol, glucose or sucrose mixtures. Specific solvent effects are found as shown by the different trends in activation parameters and in the variations of the initial state and transition state chemical potentials as observed in different media. From the results of a multiple linear correlation, it is concluded that the kinetics are controlled by the ionizing power of the solvents, their relaxation times and the outer sphere reorganization energies.

Salt effects in the kinetics of the formation of the iron(III) thiocyanate complex

The reaction between iron(III) and thiocyanate ions has been studied in several electrolyte solutions over the concentration range 0–6 mol dm–3. The observed positive kinetic salt effects may be interpreted as arising as a result of ion–solvent interactions. Support for these conclusions comes from an examination of the activity coefficients of species estimated from the treatment given by Pitzer.

Solvent effects upon reactions between ions: hexacyanoferrate(II)-peroxodisulphate and sulphite-hexacyanoferate(III)

SummaryDifferent approaches to the interpretation of solvent effects on reactions between ionic reactants are analysed, taking as a basis the kinetic data corresponding to the sulphite-hexacyanoferrate(III) and peroxodisulphate-hexacyanoferrate(III) oxidations. It is concluded that the approach based on the use of solvent parameters is the more promising, although knowledge of the transfer chemical potentials of the reactants may also be useful in the interpretation of kinetic behaviour.

Medium effects on the ligand field bands of hexathiocyanato- chromate(III)

SummaryThe wavelengths of absorption maxima are reported for two ligand field bands of hexathiocyanatochromate(III),