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LCST-Type Phase Behavior of Aqueous Biphasic Systems Composed of Phosphonium-Based Ionic Liquids and Potassium Phosphate
Although
aqueous biphasic systems (ABS) composed of phosphonium-based ionic
liquids (ILs) have demonstrated superior performance as viable media
for biocompatible extraction processes, the formation of ABS with
tetrabutylphosphonium trifluoroacetate ([P<sub>4444</sub>]ÂCF<sub>3</sub>COO) and tributyloctylphosphonium bromide ([P<sub>4448</sub>]ÂBr)
were seldom investigated. To evaluate the hydrophilicity of [P<sub>4444</sub>]ÂCF<sub>3</sub>COO and [P<sub>4448</sub>]ÂBr, the solubility
curves for the mixture of the ILs and water were determined. The influence
of temperature on the phase behavior for the [P<sub>4448</sub>]ÂBr
+ K<sub>3</sub>PO<sub>4</sub> + H<sub>2</sub>O and [P<sub>4444</sub>] CF<sub>3</sub>COO + K<sub>3</sub>PO<sub>4</sub> + H<sub>2</sub>O systems were also obtained. Results show that both [P<sub>4448</sub>]Br + H<sub>2</sub>O and [P<sub>4444</sub>]ÂCF<sub>3</sub>COO + H<sub>2</sub>O binary systems undergo lower critical solution temperature-type
phase transition, and the ABS composed of [P<sub>4444</sub>]ÂCF<sub>3</sub>COO and [P<sub>4448</sub>]Br can be formed with K<sub>3</sub>PO<sub>4</sub> at a wide range of temperatures. Moreover, the ABS
are highly temperature dependent, and biphasic region expands with
an increase in temperature. On the other hand, the capability of the
ILs to induce ABS follows the tread [P<sub>4448</sub>]Br > [P<sub>4444</sub>]ÂCF<sub>3</sub>COO. This suggests that the lower cation
hydrophilicity of ILs results in greater biphasic area in the ABS
formed by phosphonium-based ILs