Calorimetric and gas chromatographic study of hydrogen bonding in ethylene glycol and diethylene glycol


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

1Kazan Federal University, Russia

Keywords: solution thermodynamics
property: enthalpy, Gibbs energy
material: ethylene glycol, diethylene glycol

Ethylene glycol and diethylene glycol are widely used as solvents in chemistry, technology, pharmacology and industry. They are able to influence on the state of components in cellular liquids and induce an interest of investigators. A number of physicochemical properties such as isothermal compressibility, solvophobic solvation, make them similar to water. They are also an example of associated solvents. In such solvents hydrogen bonded complexes of various structure and composition can be formed. Although the thermochemical investigation of dissolved molecules in ethylene glycol and diethylene glycol is actual task, there is no extensive experimental information about solution in these solvents.

This work is dedicated to the experimental investigation of solution process in ethylene glycol and diethylene glycol. As solutes non-electrolytes molecules of various organic classes (amines, pyridines, amides, esters, ethers, nitriles and ketones) were chosen. For determination of solution enthalpies the method of semi-adiabatic solution calorimetry was used. Limiting activity coefficients were measured using gas chromatographic head space analysis. All measurements were introduced at standard state at infinite dilution. The last condition was proved by the absence of concentration dependence of measured magnitudes. Obtained enthalpies and free energies of solution were analyzed using solvation thermodynamics approach. Solution enthalpies and free energies in diols were found more endothermic as in methanol. Also comparing the solvation enthalpies in these solvents allowed to assume the solvophobic effect in diols close to zero. Using methods [1,2] the hydrogen bonding thermodynamic functions were obtained. Their values there compared with enthalpies and free energies of complexes 1:1 in base environment. The enthalpies of hydrogen bonding for weak bases were found positive, for strong bases negative and much decreased comparing with methanol. Obtained entropies of hydrogen bonding are unusually positive and can be ascribed to peculiarities of solution in associated liquids.

This 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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