Browsing by Author "Abraham, Michael H."

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Calculations on Ionic Solvation Part 1.—Free Energies of Solvation of Gaseous Univalent Ions Using a One-layer Continuum Model
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (07), 1978) Abraham, Michael H.; Liszi, János
The electrostatic free energy of solvation of an ion has been calculated using a model in which an ion of radius a and dielectric constant Îµi= 1 is surrounded by a solvent layer of thickness (b–a) and dielectric constant Îµ1, immersed in the bulk solvent of dielectric constant Îµ0. The electrostatic energy is combined with the nonelectrostatic free energy of solvation, obtained from experimental data on the free energy of solution of gaseous non-polar solutes, to yield the total free energy of solvation of a gaseous ion in a solvent. It is found that when a is taken as the ionic crystal radius, (b–a) as the solvent radius and Îµ1= 2 there is excellent agreement with experiment for the solvation of gaseous univalent cations and anions in the solvents, 1,1-dichloroethane, 1,2-dichloroethane, tetrahydrofuran, 1,2-dimethoxyethane, ammonia, acetone, acetonitrile, nitromethane, 1-propanol, ethanol, methanol and water. Limited data suggest that the method can also be applied to solution of ions in benzene, bromobenzene, chlorobenzene, ethyl benzoate, ethyl acetate and nitrobenzene.
Calculations on Ionic Solvation Part 2. Entropies of Solvation of Gaseous Univalent Ions using a One-layer Continuum Model
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (09-12), 1978) Abraham, Michael H.; Liszi, János
The electrostatic entropy of solvation of gaseous ions has been calculated using our previous model in which the ion is surrounded by a local solvent layer, immersed in the bulk solvent. The calculated electrostatic entropy is combined with the nonelectrostatic entropy of solvation, obtained from experimental data on entropies of solution of gaseous nonpolar solutes, to yield the total entropy of solvation of a gaseous ion. The only new parameters involved in the calculations are the variations with temperature of the solvent bulk dielectric constant (a known property) and the dielectric constant in the local solvent layer. We found that if the latter parameter is taken as –0.001 60 (a reasonable value for a region of low dielectric constant), there is excellent agreement with experiment for entropies of solvation of univalent cations and anions in a wide variety of aprotic solvents, and for entropies of transfer of these ions between aprotic solvents. Since no adjustable parameters are used in the calculations, the method can be used to predict entropies of solvation or of transfer in aprotic solvents. Agreement with experiment is not found for solvation entropies of ions in hydrogen bonded solvents.
Free Energies and Entropies of Transfer of Ions from Water to Methanol, Ethanol and 1-Propanol
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (08), 1978) Abraham, Michael H.; Danil de Namor, Angela F.
Solubilities of 30 1:1 electrolytes in 1-propanol have been determined and have been combined with association constants and corrections for activity coefficients to yield standard free energies of solution in 1-propanol of the ionic species (M++ X–). From like data in water, free energies of transfer from water to 1-propanol have been calculated and split into single-ion values through the assumption that ΔG°t(Ph4As+)=ΔG°t(Ph4B–); values for 12 cations and 6 anions are tabulated. The above assumption yields reasonable single-ion values which show that the free energy of simple cations and anions increases along the series of alcohols MeOH < EtOH < 1-PrOH. With previous results on enthalpies of transfer, single-ion entropies of transfer from water to 1-propanol have been calculated using both the Ph4As+/Ph4B– assumption and the correspondence plot method. Entropies of transfer from water to ethanol have also been calculated, and compared with previous results for transfer from water to methanol. For all three sets of transfers it is shown that the correspondence plot method leads to single-ion ΔS°t values of cations that are more positive by about 7 cal K–1 mol–1 than values obtained by the Ph4As+/Ph4B– assumption. On both methods of assigning single-ion values, entropies of the simple alkali halide ions are more negative in 1-propanol than in ethanol than in methanol. The prediction of ΔS°t values by Criss's boiling point method is shown to yield values for transfer to 1-propanol which are more negative than observed by only about 3 cal K–1 mol–1. Entropies of transfer of ions from water to all three alcohols are well correlated by the method of Abraham, except for the ion Ph4B– which behaves anomalously.
Heats of Solution of Electrolytes in Ethanol and Derived Enthalpies of Transfer from Water
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (02), 1978) Abraham, Michael H.; Ah-Sing, Eric; Namor, Angela F. Danil De; Hill, Tony; Nasehzadeh, Asadollah; Schulz, Ronald A.
Heats of solution of 12 1:1 electrolytes in ethanol have been determined calorimetrically, and have been extrapolated to zero electrolyte concentration to give iXH° values for these electrolytes. Together with literature data for 9 other 1:1 electrolytes, these measurements yield a set of single ion enthalpies of transfer from water to ethanol for 11 univalent cations and 6 univalent anions. Using the assumption that A/7t‘?(Ph4As+) = A//°(Ph4B~), it is shown that small univalent cations are enthalpically more stable in ethanol than in water, but that the larger tctra-alkylammonium ions are less stable in ethanol. With the same assumption, it is also shown that all the univalent cations and anions studied are of almost the same enthalpy (within about ±0.5 kcal mol-1) in the three alcohols methanol, ethanol and 1-propanol.
Thermodynamics of solution of two forms of DL-α-amino-n-butyric acid in water
(Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (1), 1977) Abraham, Michael H.; Ah-Sing, Eric; Marks, Robert E.; Schulz, Ronald A.
Two crystalline polymorphic forms of DL-α-amino-n-butyric acid have been obtained and have been shown to be identical to the A-form and B-form previously described by Iitaka and coworkers. The two forms differ in heat of solution and in their solubility in water. We find that for the A-form at 298 K, ΔH°s= 374 cal mol–1, ΔG°s= 1772 cal mol–1 and ΔS°s=–4.7 cal K–1 mol–1 and for the B-form ΔH°s= 1653 cal mol–1, ΔG°s= 1883 cal mol–1 and ΔS°s=–0.8 cal K–1 mol–1. Although the B-form is the stable form at 298 K, it is predicted from the above measurements that the A-form should be the stable form above ∼ 326 K.