New tetrapropylammonium bromide-based deep eutectic solvents: Synthesis and characterizations

Deep eutectic solvents are analogues of ionic liquids that are environmentally benign, have a range of desirable liquid properties and are easy to prepare. In this study, new tetrapropylammonium bromide (TPAB)-based deep eutectic solvents (DESs) are introduced. Different hydrogen bond donors (HBDs) - ethylene glycol, triethylene glycol and glycerol were used at different molar ratios of TPAB:HBD (1:2.5-1:5). Effects of temperature and the TPAB:HBD ratios on the DESs were investigated. Solvents of different physicochemical properties andwide liquid rangeswithminimummelting point temperatures of 249.75, 253.95 and 257.05 Kwere obtained for TPAB:ethylene glycol (1:4), TPAB:triethylene glycol (1:3) and TPAB/glycerol (1:3) respectively. The samples were further characterized in the temperature range of 293.15 to 353.15 K and the property ranges measured were density (1.096-1.218 g/cm³), viscosity (6.02-1510.0 cP), surface tension (41.9-53.2 mNm^-1), conductivity (167.2-11,500.0 μS cm^-1), refractive index (1.4466-1.4908) and pH (4.837-7.290). These demonstrate that the samples have excellent potentials for different applications. Relationships between these properties and temperature were explored. Depending on the property, the effect of temperature wasmodeled using either simple linear or Arrhenius-basedmodels. The properties of these newDESs could be predicted at different temperatures for potential applications. The potential of tunable properties makes it possible to employ DESs as a reaction medium, electrochemical process medium, solvent and absorbent. Therefore, these properties must be measured and modeled for possible use in process simulation package databases.