We have performed a systematic study of liquid‐liquid phase equilibria in aqueous and non‐aqueous solutions of tetraalkylammonium salts up to about 500 K, covering a large number of hydrogen‐bonding, dipolar aprotic and non‐polar solvents. There appear to be two different types of liquid‐liquid phase equilibria resulting from long‐range Coulombic and from short‐range specific forces, respectively. These may be denoted as Coulombic and solvophobic unmixing. Coulombic unmixing is observed in solutions of 1:1‐electrolytes in solvents of low dielectric constant, as is exemplified for solutions in hydrocarbons and long‐chain alcohols. It appears to be closely related to a general instability of ionic fluids at low reduced temperatures. Increase of the dielectric constant results in complete miscibility, as is demonstrated for salts dissolved in short‐chain alcohols and some common dipolar aprotic solvents. Solvophobic unmixing occurs if salts with large cations and anions are dissolved in water. A phenomenological analysis shows that this phase separation results from those thermodynamic pecularities which are usually attributed to the hydrophobic nature of the cations. Some cation‐anion association appears also to play a role. Similar immiscibilities have been observed with other hydrogen‐bonding solvents of high cohesive energy density, namely glycerol, ethylene glycol, 1,3‐propanediol, formamide and monoethanolamine, suggesting the existence of a more general solvophobic unmixing effect.

No abstract

No abstract

No abstract

No abstract