Mohamed F. Amira

Aquation kinetics of chloro- and bromo-pentamminecobalt(III) ions in water-acetone mixtures

SummaryThe aquation kinetics of [Co(NH3)5Cl]2+ and [Co(NH3)5Br]2+ ions in acetone-water have been investigated over a wide range of solvent compositions and temperatures. The variation of thermodynamic properties of the activated complex with the mole fraction of acetone reveals the existence of specific solvation. The correlation of the rate constant with dielectric constant of the medium is examined and discussed. A reaction mechanism which describes the solvent effect on reaction rate is proposed.

Influence of Solvent upon Rates of Ion Pair Reactions: Studies on the Aquation of Bromopentamminecobalt(III) Perchlorate in Binary/Water-Ethan-1,2-Diol Mixtures

The kinetics of the aquation of bromopentamminecobalt(III) ion have been investigated in malonate media containing different percentages of ethan-1,2-diol (up to 50%). The ion pair rate constant kip, has been determined over a wide range of malonate buffer compositions using the Wyat and Davies treatment. The thermodynamic and extrathemodynamic correlations existing between those of the association reaction (ΔG°ass, ΔH°ass, ΔS°ass) and of the ion pair aquation reaction (ΔG≠ip ΔH≠ip, ΔS≠ip) have been investigated. The kinetic solvent effects are examined in terms of the dielectric constant and water concentration effects on the ion pair rate constant. Also, the solvent effects are analysed in terms of Kamlet–Taft solvatochromic parameters and are applied successfully in mixed aqueous – ethan 1,2-diol mixtures. However, the extrema found in the change of ΔH≠ip and ΔS≠ip with the mole fraction of the co-solvent have been correlated well with that found in the change of the physical properties of the solvent–water mixtures with the solvent structure. Small changes of ΔG≠ip with the mole fraction of the solvent are attributed to a quasi-mirror image compensation between ΔH≠ip and ΔS≠ip.

Kinetics of aquation of chloropentamminecobalt(III) perchlorate in ethylene glycol-water media

SummaryThe aquation of chloropentamminecobalt(III) ion has been studied in ethylene glycol-water mixtures up to 80% by weight at five temperatures from 35 to 55°C. Specific solvent effects on the reaction rate and mechanism have been investigated and discussed. The validity of our previously proposed equations, correlating the specific reaction rate with the dielectric constant of the medium has been examined. The thermodynamic parameters of activation have been calculated and presented as evidence for the solvation effects and in support of the proposed reaction mechanism.

E.M.F. and kinetic studies of the ion-pairing effects on the rate of aquation of chloropentamminechromium(III) perchlorate in different dicarboxylate medium

SummaryRate coefficients, k, for aquation of [Cr(NH3)5Cl]2+ in 10% ethanol solutions of some dicarboxylates have been determined by potentiometric titration methods. The dissociation constants of ion-pairs so formed have been obtained from e.m.f.s. of a cell comprising glass and calomel electrodes. A wide range of k(ion) and k(ion-pair) values and dissociation constants has been obtained and a new correlation between k(ion-pair) and association constants among the dicarboxylate series studied has been established.

Solvent effects on the aquation of chloropentammine-cobalt(III) perchlorate in ethanol-water

SummaryThe aquation kinetics of the chloropenta-aminecobalt(III) ion in H2O−EtOH mixtures have been determined. A new correlation is described for calculating the chemical potential from kinetic data and molar thermodynamic excess functions for binary mixtures. The rate constants correlate well with Grunwald-Winstein solvating power Y parameter and with the dielectric constant of the medium. The data supports the D mechanism.