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Thermochemical investigation of peculiarities of hydrogen bonding in self-associated solvents


K. Zaitseva1, M. Varfolomeev1, A. Tukhbatulina1 and B. Solomonov1

1Kazan Federal University, Russia

Keywords: associated liquid, hydrogen bonding
property: enthalpy, Gibbs energy
material: hydroxyl containing compounds

The solvent is known to deeply affect the chemical reactions changing rate constants, activation parameters or even mechanism. The most significant type of non-covalent interactions influencing the properties of organic molecules is hydrogen bonding (HB). Difference in HB energy between reactants and products with solvent molecules determines the change in Gibbs energy and enthalpy of reaction. There are many methods to investigate HB in equimolar complexes. However, determination of HB parameters in associated solvents is still a problem. The net of HB explains their physicochemical properties and determines manifestation of cooperativity, reorganization and solvophobicity effects. These effects make a correct determination of HB thermodynamic parameters in associated solvents, widely used in chemistry, medicine and industry, fairly difficult task.

In current work the investigation of HB of organic molecules (amines, ketones, amides etc.) in aliphatic alcohols, ethylene and diethylene glycol, water was carried out. Semi-adiabatic solution calorimetry and gas chromatographic head space analysis were used as experimental methods. Obtained solution enthalpies and free energies were analyzed using solvation thermodynamics approach. The dependence of solvophobic effect from solute volumes, derived from consideration of solvation thermodynamics of alkanes and aromatic compounds, let to propose a method for determination of Gibbs HB energies in associated liquids. It was shown that solvophobicity do not affect the solvation enthalpies of organic solutes in aliphatic alcohols and have slight influence on solvation enthalpies in diols. The HB enthalpies and free energies of proton acceptors in associated solvents were calculated by methods [1,2]. The Gibbs HB energies in alcohols were found to approximately coincide with each other, differing from those values in water due to manifestation of strong cooperativity. The enthalpies and Gibbs energies of HB in associated liquids are not equal to values for equimolar complexes and are decreased due to reorganization. The problem of determination the HB enthalpy of solute molecules in pure water was solved by comparative analysis of HB of water and methanol. The HB entropies of solutes in associated solvents were calculated.

Work was supported by Russian Federation Government P2345

References
  1. B. Solomonov, I. Sedov, J. Mol. Liq. 139, 89 (2008)

  2. B. Solomonov, V. Novikov, M. Varfolomeev, N. Mileshko, J. Phys. Org. Chem. 18, 49 (2005)

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