Effects of constituent ions of a phosphonium-based ionic liquid on molecular organization of H₂O as probed by 1-propanol: tetrabutylphosphonium and trifluoroacetate ions

Abstract

Aqueous solutions of tetrabutylphosphonium trifluoroacetate, [P4444]CF3COO, exhibit a liquid-liquid phase transition with a lower critical solution temperature. Herein, we characterized the constituent ions, [P4444](+) and CF3COO(-), in terms of their effects on the molecular organization of H2O on the basis of 1-propanol probing methodology devised by Koga et al. The resulting characterization of the hydrophobicity/hydrophilicity is displayed on a two-dimensional map together with previous results, for a total of four cations and nine anions of typical ionic liquid (IL) constituents. The results indicate that [P4444](+) is the most significant amphiphile with strong hydrophobic and equally strong hydrophilic contributions among the group of constituent cations of ILs studied so far. The hydration number for [P4444](+) was evaluated to be nH = 72, which is three times larger than that of a typical imidazolium-based cation, [C4mim](+). Self-aggregation of [P4444](+) was found to occur in an aqueous solution of [P4444]CF3COO above 0.0080 mole fraction of the IL.

Temperature-Responsive Ionic Liquids: Fundamental Behaviors and Catalytic Applications

“…To further clarify the factors which facilicate the LCST-type phase separation of ILs with water, ILs with diverse hydrophobicity, combining phosphonium or ammonium cations with several anions, were prepared. , The LCST value of IL–water mixtures was found to increase with increasing hydrophilicity of the component ions. This indicated that the LCST-type IL–water mixture could be suitable for evaluating the hydrophilicity of target ions by determining the CST value after addition of corresponding ionic species .…”

The effect of 2,2,2-trifluoroethanol on water studied by using third derivatives of Gibbs energy, G

“…[41][42][43] Indeed, the recent report using the 1P-probing methodology found that trifluoroacetate, CF3COO -, ions are more hydrophobic than acetate, CH3COOions. 44 In order to quantify the relative hydrophobicity on the map, we evaluate the unitless distance of each plot from the origin, D defined as, 12…”

Thermoresponsive Ionic Liquid/Water Mixtures: From Nanostructuring to Phase Separation

“…For LCST, in particular, several experimental studies and simulations (see Section 4 below) emphasised the role of anions, focusing on their ability to form hydrogen bonds, which, in turn, could represent the source of the entropy that drives the LCST transition. The role of cations has been much less investigated, but two studies, in particular, provide useful insight on this aspect [ 125 , 126 ]. reference [ 125 ], for instance, applies a 2D hydrophobicity index (instead of the single hydrophobicity parameter HI of reference [ 71 , 120 ]) to quantify independently both the hydrophobicity and the hydrophilicity aspects of solutes.…”

“…The role of cations has been much less investigated, but two studies, in particular, provide useful insight on this aspect [ 125 , 126 ]. reference [ 125 ], for instance, applies a 2D hydrophobicity index (instead of the single hydrophobicity parameter HI of reference [ 71 , 120 ]) to quantify independently both the hydrophobicity and the hydrophilicity aspects of solutes. The two indices are defined in terms of suitable derivatives of thermodynamic functions [ 127 ].…”