Application of calorimetric methods to investigations of interactions in solutions

Abstract

Abstract:The results of calorimetric measurements of dissolution enthalpy of electrolytes and nonelectrolytes in aqueous mixed solvents are discussed with regard to the intermolecular interactions that occur in the solution. Particular attention is given to the systems where hydrophobic hydration can play a significant role. Several ways for analysis of the hydrophobic hydration effects are presented. In the case of the dissolution enthalpies of simple inorganic electrolyte in water-organic solvent mixtures a shape of the dependence of the standard dissolution enthalpy on the mixed solvent composition can serve as a source of information about the hydrophobic properties of the organic co-solvent. A quantitative measure of the hydrophobic properties of some organic compounds can be obtained from the analysis of the organic molecule-electrolyte (used here as a probe) enthalpic pair interaction coefficients in water, determined calorimetrically. In some cases, the 'cage model' can be used for determination of hydrophobic hydration energetic effect. This model has been applied in our laboratory for analysis of hydrophobic properties of crown ethers. It is noteworthy, that all presented methods lead to qualitatively consistent results.

Volumes, Heat Capacities, and Compressibilities of the Mixtures of Acetonitrile with N,N-Dimethylacetamide and Propylene Carbonate

“…Systematic studies on the solvation of electrolytes in binary solvents have been carried out for many years in our laboratory. At first, we examined widely the electrolyte solutions in numerous water + organic solvent mixtures. , Then we extended these studies to electrolyte solutions in binary organic solvents containing methanol (protic, hydrogen bonded solvent) − or N , N -dimethylformamide (aprotic, proton-acceptor, non-hydrogen bonded solvent). − As a continuation of these studies, we have undertaken investigations of electrolyte solutions in the mixtures of several organic solvents and acetonitrile, which due to its polarity is a good solvent for both electrolytes and nonelectrolytes. Moreover, acetonitrile molecules, in contrast to the mentioned above solvents, are not able to form H-bonds in the “classical” sense either as a proton-donor or as a proton-acceptor.…”

Enthalpy of Solvation of Monoglyme, Diglyme, Triglyme, Tetraglyme, and Pentaglyme in Mixtures of Water with N,N-Dimethylformamide at 298.15 K

“…for LPs and CPs have a similar shape. The shape of all eight curves is characteristic of hydrophobically hydrated substances, [21][22][23][24] which is reflected in the strong decrease in the enthalpy of solvation in the water-rich range (x 2 f 1) and in the linear, relatively small, slope of the curves of this function in the organic solvent-rich area. The changes in the hydration enthalpy observed in Figure 1 depend on the size of polyether molecule.…”

Effect of Temperature on the Process of Hydrophobic Hydration. Part II. Hydrophobic Hydration of 15-Crown-5 and 18-Crown-6 Ethers

“…The effect observed is connected with the hydrophobic hydration of crown ethers. The shape of all eight curves of Δ tr H m o (H 2 O → H 2 O + DMF) = f ( x 2 ) is characteristic of hydrophobically hydrated substances, ,− which is reflected in the strong decrease in the enthalpy of transfer from water to H 2 O + DMF mixtures within the water-rich range ( x 2 → 1) and in the linear, relatively small, slope of the curves of this function in the organic solvent-rich area. The values of standard dissolution enthalpy of 15-crown-5 and 18-crown-6 ethers increase with increasing temperature.…”