Thermodynamics and Computational Study of the Molecular Interactions of Imidazolium and Pyrrolidinium Based Ionic Liquids in Water

Abstract This investigation, delved into the precise determination of the thermodynamic properties in binary mixtures containing ionic liquids (ILs): a critical aspect for both process design and potential engineering applications. The focus was three specific ILs: 1‐butyl‐3‐methylimidazolium thiocyanate or chloride [Bmim][SCN] or [Bmim][Cl], and 1‐butyl‐1‐methylpyrrolidinium chloride [Bmpym][Cl], in water, at various temperatures. The primary objective was to examine the influence of temperature and ionic liquid concentration on molecular interactions within these mixtures. Experimental data for density and sound velocity were meticulously collected for the binary solutions, in the temperature range from 293.15 to 343.15 K. This data was used in calculations to derive key thermodynamic parameters, including apparent molar volume ( V φ ), apparent molar adiabatic compressibility ( k φ ), limiting apparent molar expansion , and thermal expansion coefficients ( α p ). The application of the Redlich–Mayer equation was used to determine the limiting apparent molar volume () and limiting apparent molar adiabatic compressibility along with their associated parameters ( S v , B v , S k , and B k ). Furthermore, to understand the interactions in the IL complex, the interaction energy was calculated by using density functional theory. A QTAIM and NCI analysis was done to classify the type of interactions.