Quantitative Study by Raman Spectroscopy of the Stability of 1-Methyl-3-Butylimidazolium Chloride/AlCl3/EthylAlCl2 Mixed Molten Salts in Presence of an Aliphatic Hydrocarbon

The major application of acidic 1-methyl-3butylimidazolium chloride (MBIC) EthylAlCl2 (EADC) and MBIC-AlCl3-EADC mixtures is their use as solvent for catalytic reactions such as the dimerization of olefins catalyzed by nickel complexes (Difasol process) (1-3). These ionic liquids indeed proved to be particularly effective for a two-phases catalysis process since the products are not soluble in the molten phase and can be extracted by an aliphatic hydrocarbon phase. However, the main diff iculty is to suppress or limit catalyst leaching in the organic phase and to avoid the loss of the ethylaluminum necessary for the alkylation of the nickel catalyst. A thorough quantitative investigation of the behavior of the molten salt phase as well as the organic phase has then been undertaken by Raman spectroscopy. Since the mixed mixture, containing EADC together with AlCl3, is the one used in the industrial process it has received most of our attention. If the structure of MBIC-AlCl3 and MBIC-EADC mixtures is well known (4-5), new Raman spectra confirm that the MBIC-AlCl3-EADC mixtures exhibit an additional mixed (EADC-AlCl3)Cl species which seems to play an important role in the catalytic process. The formation of such species is not quantitative and is related through an equili brium: