Synthesis, spectroscopic analysis and physicochemical characterization of TOPO and lidocaine-based deep eutectic solvents with thermal stability evaluation via TGA/DTG

Deep eutectic solvents (DESs) are a distinctive class of advanced, eco-friendly solvents regarded as a mixture of two or more constituents that display a considerably lower melting point than each single component. The exceptional physicochemical properties like low volatility, non-toxic nature, low flammability, render them perfect for numerous applications. In this work, hydrophobic DESs based on TOPO : alcohol (C7,C8,C10) as well as hydrated DES composed of Lidocane : Lauric acid with 10% and 20% H2O have been synthesized and characterized by FTIR and NMR spectroscopic studies. Spectral data show formation of DES. The thermal stability has been examined with the help of TGA/DTG. Observations indicate that both the DESs are thermally stable. The physicochemical properties such as density, viscosity, dielectric constant, refractive index and conductivity as a function of temperature, in the range of 298.15 K to 313.15 K have been measured. Density values for TOPO: Heptanol > TOPO: Octanol> TOPO: Decanol while viscosity follows reverse trend. Conductivity and dielectric constant values for TOPO: alcohol DES decrease with the alkyl chain length while increase with temperature. Refractive index values show gradual increase in the order TOPO: Heptanol < TOPO: Octanol < TOPO: Decanol. In case of Lidocane : Lauric acid DES hydrated with water, density and viscosity decrease with increase in water content while conductivity becomes very high.