The spectrophotometric solvent sorting method for the determination of free energies of transfer of individual ions—a critical appraisal

1983 ◽  
Vol 36 (9) ◽  
pp. 1739 ◽  
Author(s):  
CF Wells
Keyword(s):  
First Principles ◽  
Structural Changes ◽  
Critical Appraisal ◽  
Solvent Mixtures ◽  
Free Energies ◽  
Dominant Effect ◽  
Free Energy Of Transfer ◽  
Solvent Molecules ◽  
Energy Of Transfer

The spectrophotometric method for determining values for the free energy of transfer of the proton from water into water + co-solvent mixtures at mole fractions of co-solvent up to x2 ≈ 0.3 is examined critically from first principles. It is found that some corrections become significant at the higher x2 in this range and these are applied to all the co-solvents used. The new values for ΔGt�(H+) are then used to calculate new values for ΔGt� (X-) from ΔGt�(HX) and new values for ΔGt�(M+) and (M2+)from ΔGt�(MX) and ΔGT�(MX2). New electrochemical, solubility and pK data are incorporated into these calculations, resulting in ΔGt� values for some additional ions for several co-solvents. The ΔGt� values for all co-solvents are compared and contrasted, and it is concluded that structural changes in the solvent have a dominant effect in determining these values. The evidence for molecular rearrangements involving solvent molecules in the neighbourhood of the ions resulting from the transfer is examined.

Thermodynamics of transfer of Ph4C; scaled-particle theory and the Ph4As+/Ph4B− assumption for single ions

1979 ◽  
Vol 57 (15) ◽  
pp. 2004-2009 ◽  
Author(s):  
Michael H. Abraham ◽  
Asadollah Nasehzadeh
Keyword(s):  
Free Energy ◽  
Total Free Energy ◽  
Scaled Particle Theory ◽  
Free Energies ◽  
Particle Theory ◽  
Free Energy Of Transfer ◽  
Enthalpy And Entropy ◽  
Interaction Term ◽  
Energy Of Transfer ◽  
Entropy Of Transfer

Free energies of transfer of Ph4C from acetonitrile to 20 other solvents have been calculated from literature data. The contribution of the cavity term to the total free energy has been obtained from scaled-particle theory and Sinanoglu–Reisse–Moura Ramos theory. It is shown that there is little connection between the cavity term and the total free energy of transfer, and that there must be, in general, a large interaction term. If the latter is important for transfer of Ph4C, we argue that it must also be important for transfer of the ions Ph4As+ and Ph4B−. Previous suggestions that the interaction term is zero for transfer of these two ions are thus seen to be unreasonable. We also show, for six solvents, that the interaction term for Ph4C is very large in terms of enthalpy and entropy, and that scaled-particle theory seems not to apply to transfers of Ph4C between pure organic solvents.The free energy, enthalpy, and entropy of transfer of Ph4As+ = Ph4B− have been calculated by dividing the total transfer values into neutral and electrostatic contributions; reasonable agreement is obtained between calculated and observed values.

Solubilities of Amino Acids in Dioxane + Water Mixtures and the Determination of Transfer Free Energies of Interaction of Amino Acid from Water to Aquo-Organic Mixtures

2000 ◽  
Vol 214 (3) ◽  
Author(s):  
K. Majumder ◽  
K. Mrs. Majumder ◽  
Sujit Chandra Lahiri
Keyword(s):  
Amino Acids ◽  
Hydrophobic Interactions ◽  
Scaled Particle Theory ◽  
Solvent Mixtures ◽  
Formaldehyde Solution ◽  
Free Energies ◽  
Particle Theory ◽  
Transfer Free Energy ◽  
Organic Mixtures

The solubilities of amino acids (Glycine, α-alanine, L-asparagine, L-methionine, L-proline, L-valine, L-leucine, L-phenylalanine, L-glutamine) in dioxane-water mixtures (0-100%) have been determined colorimetrically as well as pH metrically using acid-free formaldehyde solution. The solubility decreases enormously with increase in percentage of dioxane. The results have been interpreted in terms of specific solvation and hydrophobic effects.In order to comprehend the results better, the scaled particle theory has been applied to determine the transfer free energy changes for interaction from water to aquo-organic solvent mixtures and the results are qualitatively in agreement. An estimate of the hydrophobic interactions due to constituent groups in different aquo-organic mixtures has been attempted.

Equilibrium constants and heats of formation of methyl esters and N,N-dimethyl amides of substituted benzoic acids

1992 ◽  
Vol 70 (6) ◽  
pp. 1671-1683 ◽  
Author(s):  
J. Peter Guthrie ◽  
David C. Pike ◽  
Yiu-Chung Lee
Keyword(s):  
Methyl Esters ◽  
Equilibrium Constants ◽  
Heats Of Formation ◽  
Free Energies ◽  
Ester Formation ◽  
Free Energy Of Transfer ◽  
Partition Constants ◽  
Substituted Benzoic Acids ◽  
Energy Of Transfer ◽  
Benzoyl Chlorides

Heats of methanolysis and dimethylaminolysis of substituted benzoyl chlorides (4-X-C6H4-COCl, X = H, CH3, OCH3, Cl, NO2) have been measured, as have the heats of hydrolysis of the esters, permitting the calculation of the heats of formation of the benzoyl chlorides (4-X-C6H4-COCl, X, DHf: CH3O, −80.29 ± 0.70; CH3, −48.10 ± 1.46; NO2, −47.70 ± 0.87), methyl benzoate esters (4-X-C6H4-COOCH3, X, DHf: CH3O, −124.50 ± 0.39; CH3, −93.99 ± 0.58; Cl, −92.09 ± 0.53; NO2, −92.55 ± 0.31), and N,N-dimethylbenzamides (4-X-C6H4-CON(CH3)2, X, DHf: CH3O, −75.87 ± 1.42; CH3, −46.62 ± 1.99; H, −40.96 ± 1.41; Cl, −49.33 ± 1.09; NO2, −48.05 ± 1.53). Free energies of transfer from methanol to water and from gas to water were determined for the esters and amides. Free energies of formation in aqueous solution were calculated for the acids, esters and amides, making use of thermodynamic estimation procedures where necessary. Equilibrium constants were measured for ester formation in water (X, K (M−1): CH3O, 0.14; CH3, 0.14; H, 0.12; Cl, 0.15; NO2, 0.13) and N,N-dimethylaminolysis in methanol (X, K (M−1): CH3O, 8.16; CH3, 17.5; H, 26.5; Cl, 22.6; NO2, 41.0). Partition constants for esters and amides were measured for methanol/dodecane and dodecane/water, permitting calculation of the free energy of transfer from methanol to water (4-X-C6H4-COOCH3, X, DGmw: CH3O, 3.12; CH3, 3.17; H, 3.01; Cl, 3.43; NO2, 2.89; 4-X-C6H4-CON(CH3)2, X, DGmw: CH3O, 0.96; CH3, 1.48; H, 0.92; Cl, 1.77; NO2, 0.99). These data permit calculation of the equilibrium constants for dimethylaminolysis of substituted methyl benzoates in water, and for amide formation in water (4-X-C6H4-CON(CH3)2, X, K(M−1, reactants and products as neutral molecules): CH3O, 767; CH3, 752; H, 2050; Cl, 1020; NO2, 2350). In the course of our calorimetric measurements we derived an improved value for the heat of solution of HCl in methanol.

Comparison of the free energy of transfer of electrolytes, measured with cells without transference, with the sum of the free energies of the corresponding cations and anions with the Owen-cell on standard conditions

1983 ◽  
Vol 36 (10) ◽  
pp. 1997 ◽  
Author(s):  
K Schwabe ◽  
W Hoffmann ◽  
C Queck
Keyword(s):  
Free Energy ◽  
Free Energies ◽  
Liquid Junction Potential ◽  
Liquid Junction ◽  
Ph Values ◽  
Liquid Junction Potentials ◽  
Free Energy Of Transfer ◽  
Energy Of Transfer ◽  
Very High ◽  
Junction Potential

The comparison of S2ΔS1G°tr(E1) with the sum of the values for the corresponding cation and anion S2ΔS1G°tr(Ct+)~S2ΔS1G°tr(X-) (measured) with Owen cells, gained by double extrapolation and by the assumption that the liquid junction potential at 1→0 may be neglected) gives values which differ by not more than ±5%. Most of the investigated acids allow the conclusion that the pH values, measured in cells with transference, and having the same electrodes, give good information on the acidity of the organic solvent and its water mixtures, referred to the standard state in water. That means that the pH, changed to the same H+ concentration in the solvent compared with that in water, is essentially an effect of the free energy of transfer of the hydrogen ion and not of very high liquid junction potentials.

Concerning the distant polar interaction in free energies of transfer. An explanation and an estimation procedure

1991 ◽  
Vol 69 (12) ◽  
pp. 1893-1903 ◽  
Author(s):  
J. Peter Guthrie
Keyword(s):  
Free Energy ◽  
Hydrogen Bonding ◽  
Estimation Procedure ◽  
Free Energies ◽  
Polar Interaction ◽  
Free Energies Of Transfer ◽  
Polar Groups ◽  
Polyfunctional Compounds ◽  
Free Energy Of Transfer ◽  
Energy Of Transfer

For polyfunctional compounds, free energies of transfer from gas to aqueous solution require corrections for the interactions of polar groups (Distant Polar Interactions). These corrections can be made with very few adjustable parameters by using a model of the solvation process assuming hydrogen bonding is the major source of the effect on free energy of transfer for polar groups, and that hydrogen bonding is perturbed by polar effects, measured by Taft σ*. Parameters evaluated for polyfluoro, polychloro, and polybromo compounds successfully predicted the free energies of transfer for mixed polyhalogen compounds. Preliminary parameters have been evaluated for ethers, amines, phenyl groups, nitriles, and esters. Key words: free energy of transfer, distant polar interaction, hydrogen bonding, solvation.

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