Deep eutectic solvents formed by quaternary ammonium salts and aprotic organic compound succinonitrile

Abstract

Deep eutectic solvents (DESs) are conventionally prepared by mixing quaternary ammonium salts and protic organic compounds such as alcohol, amide or carboxylic acid. In this work, we report that the DESs can also be obtained by using an aprotic organic compound such as succinonitrile (SN). The eutectic temperature was found to be 12 °C for the mixture of tetrabutylammonium trifluoromethanesulfonate (N4444Tfo) and SN at a molar ratio of 1:6, but no melting point could be observed for several DESs formed by tetrabutylammonium chloride (N4444Cl) and SN, even down to −90 °C. Fourier transform infrared spectroscopy (FTIR), Nuclear Magnetic Resonance (NMR) and theoretical calculations indicated the formation of hydrogen bonds between the anions of the ammonium salts and the methylene group of the SN, which greatly impact the melting behavior of the DESs.