Hydration of Ions in Organic Solvent and Its Significance in the Gibbs Energy of Ion Transfer between Two Immiscible Liquids

Abstract

Various kinds of cations (alkali and alkaline earth metal ions, Me4N+, Et4N+, n-Bu4N+, and tetraphenylarsonium ion) and anions (halide ions, SCN-, ClO4 -, NO3 -, and tetraphenylborate ion) have been extracted from water to nitrobenzene (NB) using several extractants: viz. tetraphenylborate and dipicrylaminate for the cations; n-Bu4N+, n-Pen4N+, n-Hep4N+, and tris(1,10-phenanthroline)iron(II) for the anions. The determination of water content in NB by means of the Karl Fischer method has confirmed that some water molecules are coextracted by hydrophilic inorganic cations and anions. Accurate numbers (n) of the coextracted water molecules per ion have been established. On the basis of these findings, a new model has been proposed for a better understanding of the Gibbs energy of ion transfer at the organic solvent/water interface. If hydrated radii of ions evaluated from n are used, conventional (Born-type) electrostatic solvation models are invalid. A new approach recognizing short-range ion−solvent interactions (e.g. hydrogen bonds) has given a better account of for the hydrated ions.

Anion Bridges Drive Salting Out of a Simple Amphiphile from Aqueous Solution

“…Figure 3 (solid line) shows the partial ion-water oxygen rdf for sodium. Integration under the first peak gives a coordination number of essentially 4 (see Table I), a value which agrees with that obtained for sodium ions in an aqueous solution from a range of measurements and simulations [19][20][21][22][23][24]. The cation therefore retains its normal hydration shell in this solution.…”

Hydration to Benzo-15-crown-5, Benzo-18-crown-6 and the Benzo-18-crown-6-Potassium Ion Complex in the Low-Polar Organic Solvents

“…The concentrations of water in the pure organic solvents equilibrated with water were determined and are listed in Table 1 38 and Kd,L = 5.50 (CTC), 39 22.8 (o-DCB), 39 24.5 (CB), 39 20 (BZ), 40 250 (CF), 41 85 (1,2-DCE), 42 and >100 (DCM) 43 for B15C5, in which the B18C6 system is shown in Fig. 1 as an example.…”

“…[1][2][3][4][5][6][7][8][9][10] Particularly, in the solvent extraction study, since the solutes in the water-saturated organic solution are discussed, hydration of the solutes in the organic phase is a very important subject. It has been demonstrated that the water molecules are coextracted with the metal ions, [11][12][13][14] the metal complexes, [14][15][16][17] and the inorganic anions 2,3,[18][19][20] into the organic solvents, and the mean hydration numbers of these solutes in the organic phase were determined.…”

“…[1][2][3][4][5][6][7][8][9][10] Particularly, in the solvent extraction study, since the solutes in the water-saturated organic solution are discussed, hydration of the solutes in the organic phase is a very important subject. It has been demonstrated that the water molecules are coextracted with the metal ions, 11-14 the metal complexes, [14][15][16][17] and the inorganic anions 2,3,[18][19][20] into the organic solvents, and the mean hydration numbers of these solutes in the organic phase were determined.There have been numerous studies about the ion-pair extraction of the crown ether complexes; extractability and selectivity of the metal ions have been discussed by using the overall extraction equilibrium constant and its component equilibrium constants. 21,22 On the other hand, in recent years, hydration of the crown ether molecules and complexes has been also studied by both the theoretical 23-31 and experimental [32][33][34][35][36][37] approaches, but most of these studies were in aqueous solution.…”

Calculation of the intrinsic solvation free energy profile of methane across a liquid/liquid interface in computer simulations

“…This similarity originates from the fact [73] that ions are transferred to the organic phase together with the water molecules constituting their first solvation shell [42,44], and hence the unfavourable case (i.e., methane in water, and hydrated ions in DCE) involves water-apolar contacts in both cases. The energy cost corresponding to these unfavourable contacts should primarily depend on the number of such contacts, i.e., the number of water molecules constituting the first hydration shell of the penetrant (as in the case of methane in water these molecules are in contact with the apolar methane molecule, whereas in the case of the hydrated chloride ion in DCE these waters are in contact with the surrounding DCE molecules).…”