Dialkylimidazolium chloroaluminate

Despite all the advantages of this process, one main limitation is the continuous catalyst carry-over by the products, with the need to deactivate it and to dispose of wastes. One way to optimize catalyst consumption and waste disposal was to operate the reaction in a biphasic system. The first difficulty was to choose a good solvent. N,N -Dialkylimidazolium chloroaluminate ionic liquids proved to be the best candidates. These can easily be prepared on an industrial scale, are liquid at the reaction temperature, and are very poorly miscible with the products. They play the roles both of the catalyst solvent and of the co-catalyst, and their Lewis acidities can be adjusted to obtain the best performances. The solubility of butene in these solvents is high enough to stabilize the active nickel species (Table 5.3-3), the nickel... 

Monophasic systems in which the ionic liquid acts as both the solvent and the catalyst, e.g. dialkylimidazolium chloroaluminates as Friedel-Crafts catalysts (see later). 

Wilkes, J. S., Levlsky, J. A, Wilson, R. A, and Hussey, C. L. [1982). Dialkylimidazolium chloroaluminate melts a new class of room-temperature ionic liquids for electrochemistry, spectroscopy and synthesis. Inorg. Chem., 21[3), pp. 1263-1264. 

J. S. Wilkes, M. J. Zaworotko, Dialkylimidazolium chloroaluminate melts A new class of room-temperature ionic hquids for electrochemistry, spectroscopy, and synthesis. 7. Chem. Soc., Chem. Comm. 1992, 965. Z. Xie, R. Bau, C. A. Reed, Free [Fe(tpp)] cation A new concept in the search for the least coordinating anion. Angew. Chem. Int. Ed. 1994, 33, 2433. 

Dimerization of re-butenes in an ionic liquid serves as basis for the new Di-fasol process for manufacturing isooctene with conversion between 70% and 80% and a very high selectivity to 90-95% of octenes. The continuous two-phase process uses the industrial Dimersol nickel catalyst dissolved in a chloroaluminate ionic liquid obtained in reaction of AICI3 and dialkylimidazolium chlorides. The ionic catalyst is retained in the IL phase that can be easily separated from the less dense organic phase of products and unreacted butenes. An important feature of the process that it works efficiently even with feeds of low butene content which makes it suitable to integrate with existing Dimersol plants. The process has been successfully operated in a pilot plant (282,285). 

Boon, J.A., Carlin, R.T., Elias, A.M. and V lkes, J.S., Dialkylimidazolium-sodium chloroaluminate ternary salt system - phase-diagram and crystal-structure, J. Chem. Crystallogr. 25 (2), 57-62 (1995). 

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