Volumetric and Spectroscopic Analysis of Betaine Hydrochloride-Protic Ionic Liquid Interaction in Aqueous Solution

The apparent molar volume and isentropic compression of betaine hydrochloride (B<middle dot>HCl) in aqueous solutions of protic ionic liquid (PIL) were determined using measurements of the solution densities and speed of sound at a pressure of 101 kPa and a temperature range of (298.15-313.15) K. In order to comprehend solute-solute, solute-solvent, and solute-cosolute interactions, the partial molar volumes at infinite dilution (V 2 degrees and K s,2 degrees) were estimated from the Masson equation. As the PIL concentration increased from 0.05 to 0.20 mol<middle dot>kg-1, the transfer volumes became positive, indicating that B<middle dot>HCl-PIL hydrophilic interactions have been enhanced. Also, structure-making or -breaking behavior of B<middle dot>HCl was examined utilizing Hepler's equation. Furthermore, UV-visible spectroscopy was employed to assess the nature of interactions with incrementing PIL concentration. The hyperchromic shift observed during the aqueous titration of B<middle dot>HCl with PIL solutions indicated the presence of hydrogen bonding interactions. A strong and attractive interaction between B<middle dot>HCl and PILs was confirmed by calculated volumetric parameters, which offer comprehensive understandings into the various interactions occurred in aqueous mixtures.