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Aqueous Biphasic Systems with Ionic Liquids
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In general terms, it can be observed that, for all the studied ILs, the miscibility of both
phases increases with temperature. Note that all the studied ILs are known as
“hydrophobic”, but the water solubility results indicate that they are substantially
“hygroscopic”. The mole fraction solubility of ILs in water ranges from 10 -3 to 10 -4 and the
water in ILs is in the order of 10 -1 . Thus, while the water-rich phase can be considered
almost as a pure phase with the dissolved IL at infinite dilution, the IL-rich phase cannot
be considered as a near pure IL phase. The results obtained for all the studied ILs show a
large difference in the mole fraction solubilities of water in ILs, ranging from 0.168 for the
[C4C1mim][Tf2N] to 0.485 for [C1mim][Tf2N]. Comparing the anions it is possible to
establish that their hydrophobicity increases from [PF6] - to [Tf2N] - both in the IL and water
rich-phases, as shown in Figure 7.
x water
Figure 7. Anion influence in the water, a), and ILs, b), mutual solubilities: , [C3mim][PF6]; ,
[C3mpy][PF6]; , [C3mim][Tf2N] 35 ; , [C3mpy][Tf2N] 41 ; , [C4mim][PF6]; , [C4mim][Tf2N] 35 .
Figure 8 shows the results for the cation family influence in the solubility of water in ILs.
16
0.45
0.40
0.35
0.30
0.25
0.20
285 290 295 300 305 310 315 320
x IL
0.0020
a) b)
T / K
0.0016
0.0012
0.0008
0.0004
0.0000
285 290 295 300 305 310 315 320
T / K