pH-dependent partitioning in room temperature ionic liquids provides a link to traditional solvent extraction behavior

Room Temperature Ionic Liquids (RTILs) are emerging as novel solvent replacements for Volatile Organic Compounds (VOCs) traditionally used in liquid/liquid separations, however, the basic science involved with fully characterizing these systems (physical properties, solubilities, partitioning of solutes, water miscibilities, etc.) may be artificially holding back utilization of these green solvents. By demonstrating the compatibility of RTILs with fundamental principles used in solvent extraction (SX), separation scientists may use the considerable expertise developed in SX techniques for novel separations with RTILs. Here, using a simple indicator dye, thymol blue, the following are demonstrated: (a) reversible pH-dependent liquid/liquid partitioning, (b) the use of CO2(g) and NH3(g) to activate the 'proton switching' of phase preference, (c) that structural variation within the RTIL ions may be utilized to fine-tune partitioning behavior, and (d) solid/liquid separations are possible with low melting ionic liquids.