abstract
This work reports on the systematic investigation of the influence of the cation alkyl side-chain length of 1-alkyl-3-methylimidazolium chloride ionic liquids ([C(n)C(l)im]Cl, with n = 1-14), as well as the substitution of the most acidic hydrogen in the imidazolium core by a methyl group, in the formation of aqueous biphasic systems. Ternary phase diagrams, tie-lines, tie-line slopes, tie-line lengths, and critical points for the several systems (ionic liquid + water + K3PO4) were determined and reported at 298 K and atmospheric pressure. It is shown that the increase of the cation alkyl chain length enhances the formation of aqueous biphasic systems if alkyl chain lengths until the hexyl are considered. The results for longer alkyl side chains show, nevertheless, that the phenomenon is more complex than previously admitted and that the capacity of the ionic liquid to self-aggregate also governs its ability to phase separate. The effect of the alkyl side-chain length on the phase-forming ability of the studied systems was quantitatively evaluated based on their salting-out coefficients derived from a Setschenow-type behavior. The aptitude of each ionic liquid for liquid-liquid demixing as a function of the cation alkyl side-chain length clearly follows three different patterns. The results obtained for the trisubstituted cation indicate that the hydrogen-bonding interactions between the ionic liquid cation and water are not a relevant issue in the formation of aqueous two-phase systems. In general, for the [C(n)C(l)im]Cl series, a multifaceted ratio between entropic contributions and the ability of each ionic liquid to self-aggregate in aqueous media control the phase behavior.
keywords
MUTUAL SOLUBILITIES; PHASE-SEPARATION; 2-PHASE SYSTEMS; SALTING-OUT; 1-BUTYL-3-METHYLIMIDAZOLIUM BROMIDE; POLY(ETHYLENE GLYCOL); 298.15 K; WATER; EXTRACTION; TEMPERATURE
subject category
Chemistry
authors
Freire, MG; Neves, CMSS; Lopes, JNC; Marrucho, IM; Coutinho, JAP; Rebelo, LPN
our authors
Catarina Maia Seco Seiça Neves
Assistant Researcher
Isabel Maria Delgado Jana Marrucho Ferreira
Full professor
Mara Guadalupe Freire Martins
Coordinating ResearcherGroups
G4 - Renewable Materials and Circular Economy
G5 - Biomimetic, Biological and Living Materials
Projects
acknowledgements
This work was financed by national funding from FCT, Fundacao para a Ciencia e a Tecnologia, through the Projects PTDC/QUI-QUI/121520/2010 and Pest-C/CTM/LA0011/2011. The authors also acknowledge FCT for the postdoctoral and doctoral Grants SFRH/BPD/41781/2007 and SFRH/BD/70641/2010 of M.G.F. and C.M.S.S.N., respectively.