Aqueous biphasic system formation using 1-alkyl-3-ethylimidazolium bromide ionic liquids as new extractants

• The new class of 1-alkyl-3-ethylimidazolium bromide ionic liquids was synthesized.
• The building of aqueous biphasic system (ABS) was studied.
• IL with ethyl group in the imidazolium N-3 position better form ABS compared to IL containing methyl substituent.
• Longer alkyl chain in the imidazolium N-1 position better forms ABS due to increasing ionic liquid hydrophobicity and poorer affinity for water.
• Extraction of selected organic dyes was performed to demonstrate application of studied ionic liquids as novel extractants.

In this work three 1-alkyl-3-ethylimidazolium bromide ionic liquids (alkyl = ethyl, hexyl and octyl) were synthesized applying both, conventional and microwave assisted synthetic paths. The phase diagrams for aqueous solutions of 1-alkyl-3-ethylimidazolium bromide ionic liquids as novel extractants combined with phosphate-based salts are reported and discussed in terms of aqueous biphasic system (ABS) formation. Merchuk equation was applied in order to correlate the experimental binodal data. The liquid–liquid equilibrium data (tie-line compositions and tie-line length) were also experimentally determined by a gravimetric method. The influence of the alkyl chain length on ABS formation ability was investigated. It was found that ability to form ABS increases with the increase of the alkyl chain length on the imidazolium cation. Also, it was found that ionic liquids with ethyl group in the N-3 position better form ABS compared to those with methyl substituent. This was discussed in terms of increasing ionic liquid hydrophobicity and poor affinity for water. In order to better understand the impact of the alkyl side chain of the imidazolium ion and the efficiency of ABS formation, computer simulations were performed using investigated ionic liquids with the ethyl group in the position N-3 of the cation and different alkyl substituents in the position N-1. Also, extraction of selected organic dyes was performed to demonstrate application of studied ionic liquids as novel extractants.

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