Kiron K. Kundu

Ion—solvent interactions in acetonitrile + water mixtures

Abstract Standard Gibbs energies of transfer, Δ G ° t of alkali metal chlorides (M = Li, Na, K, Rb and Cs) and potassium bromide and iodide from water to the aqueous mixtures of 20, 40, 60 and 80 mass per cents of acetonitrile (ACN) have been determined at 25°C from emf measurements performed on the double cell comprising AgAg X and M (Hg) electrodes. The individual ionic contributions to Δ G ° t have also been evaluated using the reference electrolyte (RE = Ph 4 AsBPh 4 ) method, the required Δ G ° t s of the RE being obtained from the measured solubilities of salts viz . Ph 4 AsPic, KBPh 4 and KPic (Pic = picrate and Ph = phenyl). The observed increasing Δ G ° t values of the halide ions X − and their order Cl − ⪢ Br − ⪢ I − furnish the thermodynamic evvidence for the effect of the well known decreased H-bonding and the anion destabilizing propensities of dipolar aprotic cosolvent ACN. But the observed shallow minima in Δ G ° t -composition profiles for M + and H + are indicative of the result of the oppositg effects of water structure breaking propensities and the protophobic character of ACN and their relative order is the combined effects of acid—base, Born-type and soft—soft interactions. Moreover, while the distinctly pronounced stabilization of large tetraphenyl ionshas been ascribed as the combined effects of dispersion and cavity-forming interactions, the less pronounced solvation of Pic − has been attributed to the combined effects of increased dispersion interactions of benzene nucleus and of decreased H-bonding interactions of O-atoms of the substituents. These contentions have been further substantiated by comparing Δ G ° t ( i ) values of some selected ions in ethylene glycol—water mixtures.

Standard potentials of Li/Li+, Na/Na+ and K/K+ electrodes in ethylene glycol and its aqueous mixtures at 25°C and the related thermodynamic behaviour of the alkali halides.

Abstract Standard potentials ( s E o ) of M/M + (M = Li, Na and K) electrodes in ethylene glycol and its aqueous mixtures have been determined at 25°C from emf measurements of the cells of the type M y (Hg)|MBr(m), solvent|AgBr/Ag, the ( s E o ) values of the AgBr/Ag electrode being known from earlier studies. These potentials along with the known ( s E o ) values of AgX/Ag (X = Cl, Br and I) electrodes were utilised to compute the s E o values of the complete cells comprising MX electrolytes in these solvents, which in turn helped in computing standard free energies of transfer Δ G t o (MX) of MX electrolytes from water to aqueous glycol solvents. These values as well as those in aquomethanolic solvents, computed from the relevant literature data, were analysed from the point of ion-solvent interactions. Also, G t o (i) values for the individual ions, computed by the ‘simultaneous extrapolation’ of the linear plots of Δ G t o (HX) and Δ G t o (HCl — HX) against ( r x − ) −1 to ( r x − ) −1 = 0, in both the solvents suggest that the cations are solvophilic and the halide ions are hydrophilic in nature. Furthermore, the variation of the values of Δ G t o (i) and more appropriately, of Δ G o t,ch (i) with solvent composition has been found to be in fairly good agreement with what is expected from the consideration of the interaction energies of the ionic species with the positive or negative charge centres of the isolated dipoles.

Ion-solvent interactions in dimethylformamide + water mixtures

Abstract Standard Gibbs energies of transfer, ΔG°t, of MCl (M = Li, Na, K, Rb and Cs) and K X (X = Br and I) have been determined by use of the double cells comprising M(Hg) and AgXAg electrodes in some aqueous mixtures of DMF at 25°C. These values were dissected into individual ion contributions using TATB reference electrolyte assumption, as obtained by measuring the solubility products of the salts viz. KPic, KBPh4 and Ph4AsPic. The observed increasingly positive magnitudes of ΔG°t of the halide ions and the increased negative magnitudes of the cations including H+, reflect the well known anion-destabilization and the larger “basicity” and cationotropism of the aqueous mixtures of this co-solvent. And the observed distinctly flat regions of ΔG°t curves of cations over an intermediate composition are attributable to strong intercomponent interactions. Comparison of the results with those in DMSO—water are ACN—water mixtures reveals that the solvating characteristics of DMF—water are somewhat similar to that of DMSO—water but different from that of ACN—water mixtures. Moreover, while the observed relative behaviour of Pic− are found to be guided by the combined effects of dispersion interactions and anion destabilisation of these co-solvents, that of the large-sized tetraphenyl ion is, however, guided by the combined effects of dispersion interactions as well as the “cavity-forming” interactions as estimated in the light of scaled particle theory.

Solvation of ions. XXVII. Comparison of methods to calculate single ion free energies of transfer in mixed solvents

AbstractFree energies of transfer of ions from water to mixtures of water with acetonitrile (AN), with dimethylformamide (DMF), with dimethylsulfoxide (DMSO), and with ethylene glycol have been determined using both the tetraphenylarsonium tetraphenylboride [TATB] and the negligible liquid junction potential [Ej] assumptions. By making use of ΔGtr(Ag+)[TATB]=12 kJ-mol−1 for transfer from DMSO to AN and by assuming negligible liquid junction potential in the cell

Transfer free energies of some ions from water to dimethylsulfoxide-water and urea-water mixtures

{\text{Ag|AgNO}}_{\text{3}} {\text{(0}}{\text{.01}}M{\text{),S}}\parallel {\text{Et}}_{\text{4}} {\text{NPic(0}}{\text{.1}}M{\text{),AN}}\parallel {\text{AgNO}}_{\text{3}} {\text{(0}}{\text{.01}}M{\text{),AN|Ag}}

Medium Effects on Deprotonation of Mono- and Di-protonated Piperazines in Binary Aqueous Mixtures of some Protic, Aprotic and Dipolar Aprotic Cosolvents

single ion free energies of transfer of silver ion ΔGtr(Ag+)[Ej] from DMSO to 35 pure and mixed solvents show a standard deviation of only 2 kJ-mol−1 when compared with ΔGtr(Ag+) calculated from the TATB assumption that ΔGtr(Ph4As+)=ΔGtr(Ph4B−). The ferrocene assumption [Fc] also gives acceptable agreement with ΔGtr(Ag+)[TATB] provided that the solvents are not highly aqueous. Other cells with other junctions give less acceptable agreement between the Ej and TATB assumptions. It is essential that the salt bridge is always tetraethylammonium picrate in AN, if the Ej assumption is assumed. Because of the ease of making potentiometric measurements compared with the difficulty of measurements required for the TATB assumption, the negligible liquid junction potential method in the cell shown is recommended for estimating transfer free energies of single ions. The ferrocene assumption is acceptable only for non-structured aprotic solvents.

Free energies and entropies of transfer of hydrobromic and hydroiodic acids from water to t-butyl alcohol + water mixtures from electromotive force measurements at different temperatures (5—35°C)

The standard potentials (E°) of the silver/silver-iodide electrode in aqueous mixtures of ethylene glycol (containing 10, 30, 50, 70 and 90 wt-% glycol) have been determined from emf measurements of the cell Pt, H2(g, 1 atm)/HOAc(m1), NaOAc(m2), Kl(m3), solvent/AgI/Ag at nine temperatures ranging from 5 to 45°C. These E° values have been utilized to compute free energy (Δtt°), entropy (ΔSt°) and enthalpy (ΔHt°) changes accompanying the transfer of HI from water to each of the solvents. These values as well as those for HCl and HBr and obtained earlier have also been utilized to evaluate ΔSt°(i) for individual ions by a method of ‘simultaneous extrapolation,’ which in turn furnished the values of ΔHt°(i) for these ions. These quantities and also the ‘chemical’ contributions for the halide ions as obtained by subtracting the ‘electrostatic’ contribution computed with the Born equation, have been examined in the light of ion—solvent interactions as well as the structural changes of the solvents. The observed results conform with what is expected from the competitive effects of the preferential solvating capacities of water towards halide ions and that of other solvents towards hydrogen ions, and also of the effects arising from the structural changes of the solvents that are likely to occur in the over-all transfer process.

Free energies and entropies of transfer of hydrogen halides from water to aqueous alcohols and the structure of aquo-organic solvents

The standard free energies of transfer (ΔGto) of some electrolytes from water to aqueous mixtures of dimethylsulfoxide (DMSO) and of urea have been split into the contribution from individual ions by use of the reference electrolyte Ph4AsBPh4 (RE), where Ph=phenyl. For each of the solvents, ΔGto(Ph4AsBPh4) was determined from the solubility products of the salts KBPh4, Ph4AsPi, and KPi, where Pi=picrate ion. The observed ΔGto(i) values for the individual ions are strikingly different from the corresponding values obtained by the simultaneous extrapolation (SE) procedure reported earlier.