Calculations on ionic solvation-V The calculation of partition coefficients of ions

Michael H. Abraham, János Liszi

Research output: Article

108 Citations (Scopus)


The solvation free energy of an ion in an organic solvent is calculated using our new electrostatic method, and is combined with the hydration free energy to yield the free energy of transfer of the ion from water to the organic solvent. It is shown that for the solvent systems water/1,2-dichloroethane, dichloromethane, chloroform, o-dichlorobenzene, chlorobenzene, and nitrobenzene there is good agreement between the calculated ΔGto values and the free energies for partition of ions, ΔGpo = -RTlnP. For organic phases in which water is quite soluble, for example 1-octanol, 1-pentanol, isopentanol, ethyl acetate, and methylisobutylketone, the calculated ΔGto values are always more positive than the observed partition values, ΔGpo. It is shown that this effect is due to hydration of the ions in the wet organic phase and by calculations on a solvation model in which an ion in the wet organic phase is surrounded by a layer of water of thickness 3.1 Å (the diameter of a water molecule) it is concluded that in the first group of solvents most ions are unhydrated in the wet organic phase; Cl- is an exception and is partially hydrated. In the second group of wet solvents, all ions are at least partially hydrated, and Cl- is hydrated by a layer of water that must be even thicker than the diameter of a water molecule.

Original languageEnglish
Pages (from-to)143-151
Number of pages9
JournalJournal of Inorganic and Nuclear Chemistry
Issue number1
Publication statusPublished - 1981


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