Dialkylimidazolium hexafluorophosphate

Domarfska, U., Marciniak, A., and Bogel-Lukasik, R., Phase equilibria (SLE, LLE) of N, N-dialkylimidazolium hexafluorophosphate or chloride, in Ionic Liquids lllA Fundamentals, Progress, Challenges, and Opportunities Properties and Structure, R.D. Rogers and K.R. Seddon (Eds), Washington, D.C., 2005 ACS, NY, 2003. 

The use of quaternary phosphonium salts and 1,3-dialkylimidazolium hexafluorophosphates in green organic synthesis 07COC107. 

Keglevich G, Grun A, Hermecz I, Odinets L (2011) Quaternary phosphonium salt and 1, 3-dialkylimidazolium hexafluorophosphate ionic liquids as green chemical tools in organic syntheses. CurrOrg Chem 15 3824-3848... 

Reichert, W.M., Holbrey, J.D., Swatloski, R.P., Gutowski, K.E., Visser, A.E., Nieuwenhuyzen, M., Seddon, K.R. and Rogers, R.D., Solid-state analysis of low-melting 1,3-dialkylimidazolium hexafluorophosphate salts (ionic liquids) by combined x-ray crystallographic and computational analyses, Cryst. Growth Des. 7 (6), 1106-1114 (2007). 

The Heck reaction is a C-C coupling reaction where an unsaturated hydrocarbon or arene halide/triflate/sulfonate reacts with an alkene in presence of a base and Pd(0) catalyst so as to form a substituted alkene. Kaufmann et al. showed that the Heck reaction carried out in presence of ILs such as tetra-alkyl ammonium and phosphonium salts without the phosphine ligands, resulted in high yields of product. They attributed the activity to the stabilizing effect of ammonium and phosphonium salts on Pd(0) species. Carmichael et al. used ionic liquids containing either A,A -dialkylimidazolium and A-alkylpyridinium cations with anions such as halide, hexafluorophosphate or tetrafiuoroborate to carry out reactions of aryl halide and benzoic anhydride with ethyl and butyl acrylates in presence of Pd catalyst. An example of iodobenzene reacting with ethyl acrylate to give trans-et vy cinnamate is shown in Scheme 14. 

Domariska, U. and Mazurowska, L., Solubility of 1,3-dialkylimidazolium chloride or hexafluorophosphate or methylsulfonate in organic solvents. Effect of the anions on solubility. Fluid Phase Equilib., 221, 73, 2004. 

Ionic liquids have recently appeared as clean alternatives to classical organic solvents for a wide variety of biochemical processes due to their unique properties [22-26]. Ionic liquids are organic salts which are liquid close to room temperature. They normally consist of an organic cation (e.g. dialkylimidazolium, tetraalkylam-momium) and a polyatomic inorganic cation (e.g. hexafluorophosphate, tetrafluoroborate, bis(trifluoromethylsulphonyl)imide) (Fig. 8.2). 

All 1,3-dialkylimidazolium ILs reported to date are hygroscopic, and their miscibility with water is largely controlled by the nature of the anion. While those salts containing the nitrate, chloride and perchlorate anions are usually miscible with water in all proportions, those associated with hexafluorophosphate and bis(tri-fluoromethane) sulfonylamidate anions are almost completely immiscible with water [93]. Interestingly, the miscibility with water of those containing the tetraf lu-oroborate anion is temperature dependent (Fig. 3.5-7) [36]. It is also known that an increase of the N-alkyl chain lengths increases the hydrophobicity for a series of 1-alkyl-3-methylimidazolium hexafluorophosphate ILs [94] The miscibility of water with ILs can be increased by the addition of short-chain alcohols [95] or diminished by the addihon of salts (salting-out effect) [96]. 

The real breakthrough in the use of ionic liquids as solvents came in 1992, when Wilkes and Zaworotko studied the formation of dialkylimidazolium salts associated with water-stable anions. This led to the discovery of the ionic liquids [emim][BF4] 5 (Figure 2.2) and [emim][N03], with melting points of 15°C and 38" C, respectively. These ionic liquids are hygroscopic, but they are not degraded in the presence of moisture. Shortly afterward, the synthesis of the corresponding hexafluorophosphate derivative 6 was described. Today, most ionic liquids are based on imidazolium derivatives associated with non-covalent anions. 

Dialkylimidazolium-based tetrafluoroborate and hexafluorophosphate were the most studied ILs because of their facile preparation and purification process. It was well known that these anions would be degraded when contacted with moisture or exposed to microwaves, heat, and so on. Although the two anions all could produce F in the process of degradation, there was still a difference in the final products. 

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