Synthesis and Thermophysical Properties of Biocompatible Cholinium-Based Amino Acid Ionic Liquids

Nowadays the knowledge of thermodynamic properties for amino acid ionic liquids (AAILs) has been paramount for the design of many chemical processes. In this present work, a series of cholinium-based AAILs ([Ch][AA]) were synthesized by neutralization of choline hydroxide solution with five amino acids and then were characterized by H-1 NMR, Fourier transform infrared (FT-IR), elemental analysis, thermogravimetry, and differential scanning calorimetry (DSC) analysis. Physico-chemical properties such as density, viscosity, refractive index, and conductivity were measured and correlated with the empirical equations in a wide temperature range. The thermal expansion coefficient values were also calculated from the acquired experimental density values. From the experimental data, it was found that the density, viscosity, and refractive index decreased while conductivity increased with the increase of temperature. The correlation results were proposed to be in good agreement with the experimental data, and optimal fitting parameters were presented. In addition, the coefficient of thermal expansion was considered to be independent of temperature in the range of (298.15 to 353.15) K.