The effect of the cation alkyl chain branching on mutual solubilities with water and toxicities


The design of ionic liquids has been focused on the cation-anion combinations but other more subtle approaches can be used. In this work the effect of the branching of the cation alkyl chain on the design of ionic liquids (ILs) is evaluated. The mutual solubilities with water and toxicities of a series of bis(trifluoromethylsulfonyl)-based ILs, combined with imidazolium, pyridinium, pyrrolidinium, and piperidinium cations with linear or branched alkyl chains, are reported. The mutual solubility measurements were carried out in the temperature range from (288.15 to 323.15) K. From the obtained experimental data, the thermodynamic properties of the solution (in the water-rich phase) were determined and discussed. The COnductor like Screening MOdel for Real Solvents (COSMO-RS) was used to predict the liquid-liquid equilibrium. Furthermore, molecular dynamic simulations were also carried out aiming to get a deeper understanding of these fluids at the molecular level. The results show that the increase in the number of atoms at the cation ring (from five to six) leads to a decrease in the mutual solubilities with water while increasing their toxicity, and as expected from the well-established relationship between toxicities and hydrophobicities of ILs. The branching of the alkyl chain was observed to decrease the water solubility in ILs, while increasing the ILs solubility in water. The inability of COSMO-RS to correctly predict the effect of branching alkyl chains toward water solubility on them was confirmed using molecular dynamic simulations to be due to the formation of nano-segregated structures of the ILs that are not taken into account by the COSMO-RS model. In addition, the impact of branched alkyl chains on the toxicity is shown to be not trivial and to depend on the aromatic nature of the ILs.



subject category

Chemistry; Physics


Kurnia, KA; Sintra, TE; Neves, CMSS; Shimizu, K; Lopes, JNC; Goncalves, F; Ventura, SPM; Freire, MG; Santos, LMNBF; Coutinho, JAP

our authors


This work was financed by national funding from Fundacao para a Ciencia e a Tecnologia (FCT, Portugal), European Union, QREN, FEDER and COMPETE by the projects PEST-C/CTM/LA0011/2013, PEST-C/EQB/LA0020/2013, PEST-OE/QUI/UI0100/2013, PTDC/AAC-AMB/119172/2010 and FCT-ANR/CTM-NAN/0135/2012 (including a post-doctoral grant of K. S.). The authors also thank FCT for the doctoral and post-doctoral grants SFRH/BD/70641/2010, SFRH/BPD/79263/2011, SFRH/BD/85871/2012, SFRH/BPD/88101/2012 of C. M. S. S. Neves, S. P. M. Ventura, T. E. Sintra, and K. A. Kurnia, respectively. M. G. Freire acknowledges the European Research Council (ERC) for the Grant ERC-2013-StG-337753.

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