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·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 (V2° and Ks,2°) were estimated from the Masson equation. As the PIL concentration increased from 0.05 to 0.20 mol·kg–1, the transfer volumes became positive, indicating that B·HCl–PIL hydrophilic interactions have been enhanced. Also, structure-making or -breaking behavior of B·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·HCl with PIL solutions indicated the presence of hydrogen bonding interactions. A strong and attractive interaction between B·HCl and PILs was confirmed by calculated volumetric parameters, which offer comprehensive understandings into the various interactions occurred in aqueous mixtures.