Study of the solvation process of some pyrazole derivatives in three different solvents by solution calorimetry and IR spectroscopy: Unravelling solute-solvent interactions

Abstract

The study of the relationship between intermolecular interactions present in the solvation process and the magnitude of thermodynamic properties is extended from imidazole to pyrazole derivatives. The enthalpies of solution of pyrazole, 3,5-dimethylpyrazole and 3,4,5-trimethylpyrazole were calorimetrically determined in the solvents water, methanol and acetonitrile. The enthalpy of solution values for the three compounds in the three solvents are endothermic and spontaneous with an increase in entropy. As in the case with imidazole derivatives, the formation of a solution of pyrazole derivatives creates liquids that are more structured thermodynamically. The enthalpy of sublimation for 3,4,5-trimethylpyrazole, which is not available in the literature, was determined by the Knudsen effusion method. The combination of these thermodynamic properties has allowed the corresponding enthalpies of solvation to be obtained for the three pyrazole derivatives in the three selected solvents. With the use of the Pierotti equations and the enthalpies of solvation, the enthalpies of cavity formation were calculated along with the corresponding solute-solvent enthalpies of interaction. The infrared spectra and molecular volumes, as estimated through the electronic density, were used to obtain molecular insights into the solvation sensible sites within the studied solute molecules. The discussion of the solvation process and enthalpies of interaction of the pyrazole derivatives is based on the molecular structural features of solutes, specific intermolecular interactions and protic or aprotic nature of the solvents. The use of any empirical parameters in the discussion of the results was avoided.