Two new ionic liquids derived from biological buffers, N-(2-hydroxyethyl)piperazine-N′-(3-propanesulfonic acid) (EPPS) or 3-(cyclohexylamino)-1-propanesulfonic acid (CAPS), with tetramethylammonium hydroxide (TMA) have been synthesized by simple acid-base neutralization method. The molecular structures of these two ionic liquids, [TMA][EPPS] and [TMA][CAPS], were confirmed by using nuclear magnetic resonance (NMR) analysis. The thermal stabilities and the melting points of the ionic liquids were determined by using thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) techniques, respectively. Water contents in the prepared ionic liquids were measured with Karl Fischer titration.
The physical properties, including density, thermal expansion, apparent molar volume, solubility, viscosity, conductivity, and molar conductivity, of the binary ionic solutions of [TMA][EPPS] and [TMA][CAPS] with water or organic solvents have been determined over wide temperature and concentration ranges under atmospheric pressure. Several correlated equations as a function of temperature or concentration were used to fit the physical properties data which are a polynomial equation for density, the Vogel-Fulcher-Tammann equation for viscosity, the Casteel-Amis equation for conductivity, and the Debye-Hückel-Onsager equation for molar conductivity. In addition, the Walden plot was used to represent the ionicity of ionic liquids. These two new ionic liquids were found to be soluble in water and in organic solvents, such as methanol and ethanol. As a consequence, these two new ionic liquids could be applied to broad applications in which the systems containing either water or organic solvents.

Two new ionic liquids derived from biological buffers, N-(2-hydroxyethyl)piperazine-N′-(3-propanesulfonic acid) (EPPS) or 3-(cyclohexylamino)-1-propanesulfonic acid (CAPS), with tetramethylammonium hydroxide (TMA) have been synthesized by simple acid-base neutralization method. The molecular structures of these two ionic liquids, [TMA][EPPS] and [TMA][CAPS], were confirmed by using nuclear magnetic resonance (NMR) analysis. The thermal stabilities and the melting points of the ionic liquids were determined by using thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) techniques, respectively. Water contents in the prepared ionic liquids were measured with Karl Fischer titration.
The physical properties, including density, thermal expansion, apparent molar volume, solubility, viscosity, conductivity, and molar conductivity, of the binary ionic solutions of [TMA][EPPS] and [TMA][CAPS] with water or organic solvents have been determined over wide temperature and concentration ranges under atmospheric pressure. Several correlated equations as a function of temperature or concentration were used to fit the physical properties data which are a polynomial equation for density, the Vogel-Fulcher-Tammann equation for viscosity, the Casteel-Amis equation for conductivity, and the Debye-Hückel-Onsager equation for molar conductivity. In addition, the Walden plot was used to represent the ionicity of ionic liquids. These two new ionic liquids were found to be soluble in water and in organic solvents, such as methanol and ethanol. As a consequence, these two new ionic liquids could be applied to broad applications in which the systems containing either water or organic solvents.

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