Room temperature ionic liquids miscibility

Xiong, H.Y., Chen, T., Zhang, X.H., and Wang, S.R, Electrochemical property and analysis application of biosensors in miscible nonaqueous media-room temperature ionic liquid, Electrochem. Commun., 9,1648-1654,2007. 

More recently, two-phase solvent systems, sometimes with temperature-dependent mutual miscibility of the two components, have gained interest as reaction media [149-156]. Having different solubilities for educts, products, reagents, and catalysts, biphasic solvent combinations can facilitate the separation of products from reaction mixtures. Since perfluorohydrocarbons [149-154] and room temperature ionic liquids [155, 156] are immiscible with many common organic solvents, they are particularly suitable for the formation of such biphasic solvent systems see also Section 5.5.13. 

Typically, the reaction is performed in a liquid-liquid biphasic system where the substrates and products (upper phase) are not miscible with the catalyst/ionic liquid solution (lower phase). The SiH-functional polydimethylsiloxane and the olefin are placed in the reaction vessel and heated up to 90 °C. Then the precious metal catalyst (20 ppm) and the ionic liquid (1 %) are added. After complete SiH conversion, the reaction mixture is cooled to room temperature and the products are removed from the reaction mixture by either simple decantation or filtration (in case of non-room-temperature ionic liquids). The recovered catalyst/ionic liquid solution can be reused several times without any significant change in catalytic activity. A treatment or workup of the ionic liquid-catalyst solution after each reaction cycle is not necessary. The metal content of the products was analyzed by ICP-OES (Inductively coupled plasma optical emission spectroscopy) and the chemical identity of the organomodified polydimethylsiloxane was verified by NMR spectroscopy. 

Room temperature ionic liquids are receiving much attention as environmentally benign solvents. They display negligible vapor pressure, high ionic conductivity, and limited miscibility with water and common organic solvents [119]. The chemistry of ionic liquids is a rapidly expanding field. 

In order to look at the effect of water on the structure of both hydrophobic and hydrophilic room-temperature ionic liquids, SFG measurements were taken at water partial pressures of 5 X 10 Torr and 20 Torr. Results showed that ionic liquid behaviour at the surface differed depending on whether the ionic liquid was hydrophobic or hydrophilic. For hydrophobic ionic liquids, the imidazolium ring reorients towards the surface normal upon addition of water, while for hydrophilic ionic liquids, the ring remains flat on the surface. The process was found to be reversible, with the tilting of the cation attributed to the interaction of water with C(2)—H. Moreover, for water-miscible ionic liquids, water molecules were said to be... 

It was John Wilkes who realized that room-temperature molten salts would only experience a widespread interest and uptake if they were stable under environmental conditions. Wilkes group published details of the first such liquid in 1992 using the BF]j" and the PFj anions, the latter showing a miscibility gap with water. Thus these liquids could, in principle, be made water free. (Today we know that ionic liquids containing BFJ and PF are subject to decomposition in the presence of water.) Electrochemical studies showed that even these early ionic liquids had wide electrochemical windows of about 4 V with cathodic limits of-2 to -2.5 V. vs. NHE. This cathodic limit should, from the thermodynamic point of view, be wide enough to electrodeposit many reactive elements. 

For the purpose of developing ionic liquids which molecularly dissolve biopolymers, we designed ether-containing N, IV -dialkyl imidazolium derivatives 26,27 [120]. These compounds are obtained as solid after tfeeze drying. They eventually become liquid at room temperature in air, probably due to absorption of water from the atmosphere. These ionic liquids were miscible with water. The content of water in these ionic liquids was 2.6 wt% for 26 and 2.5 wt% for 27, as determined by Karl Fischer s method. To compare the solvent properties of these ionic liquids with conventional ionic liquids, compound 25 was saturated with water (water content, 2.5 wt%) and used as a reference. 

---