Thermodynamics Research Center / ThermoML | Thermochimica Acta

ABSTRACT

Reactivity and properties of organic molecules in self-associated liquids greatly depend on the hydrogen bonding with solvent. Thus, the determination of the thermodynamic functions of hydrogen bonding between solute and solvent molecules causes a practical interest. This work contains an entire thermodynamic analysis of hydrogen bonding of aliphatic and aromatic amines in associated solvent methanol. The enthalpies of solution at infinite dilution and limiting activity coefficients for studied systems were measured experimentally for this purpose. Enthalpies and Gibbs energies of specific interaction of amines with neat methanol were determined. These values were found to be decreased comparing with thermodynamic functions of hydrogen bonding in equimolar complexes "methanol-amine" determined in inert solvent or base media. The linear dependence between enthalpies and Gibbs energies of specific interactions of amines with neat methanol was observed. It was firstly revealed that the entropy of specific interactions of amines with neat methanol can be about zero or positive. Obtained results show that one of the most important steps in the process of dissolution of amine in methanol is the reorganization of solvent-solvent hydrogen bonds. It was found, that the cooperative effect of adjacent hydrogen bonds has an impact on the Gibbs energies of specific interaction of amines in methanol, but its value is significantly smaller than in water solutions. A new view on determination and analysis of thermodynamic functions of the specific interaction of solute with methanol is presented in this work. The new results show that the process of hydrogen bond formation in the self-associated solvents are significantly different from the hydrogen bonding in the 1:1 complexes formed in aprotic solvents.