Preparation of ternary hydrophobic magnetic deep eutectic solvents and an investigation into their physicochemical properties

Abstract

Hydrophobic magnetic deep eutectic solvents (HMDESs) are considered a subclass of DESs comprised of a hydrogen bond acceptor (HBA), hydrogen bond donor (HBD), and a metal halide salt. These DESs can be easily manipulated by an external magnet and employed in numerous applications including liquid–liquid extractions and catalysis. In this work, a total of forty-six (46) HMDESs were prepared and their physicochemical properties studied. Six structurally unique ionic and non-ionic HBAs were combined with lanthanide and transition metal halide salts and twelve different HBDs to prepare room temperature eutectic solvents. The viscosities of HMDESs ranged from 46 centipoise (cP) to 124,600 cP at 23 ℃. Their magnetic susceptibilities, studied by superconducting quantum interference device (SQUID) magnetometry and a magnetic susceptibility balance, varied from 3.03 Bohr magnetons (μB) to 9.32 μB when the type of metal halide salt and its molar ratio were varied. Thermal stabilities ranged from 151.1 ℃ to 308.5 ℃ at 5% mass loss. All HMDESs comprised of ionic HBA were observed to be insoluble in hexane. This study demonstrates that the physicochemical properties of HMDESs can easily be tailored by varying the DES constituents as well as their molar ratio. The structural tunability of these solvents make them highly attractive candidates for a plethora of applications ranging from extractions to electrochromic applications, where HMDESs can be easily manipulated by an external magnetic field.