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Measurements and modelling of antioxidants’ solubility in ionic liquids


E. Alevizou1 and E. Voutsas1

1National Technical University of Athens, Greece

Keywords: ionic liquids, modelling, COSMO-RS
property: solubility
material: cinnamic acid derivatives

Room temperature ionic liquids (ILs) have received increased interest as potential replacements for volatile organic solvents, essentially due to their negligible vapour pressures. Ionic liquids are typically salts composed of relatively large organic cations and inorganic or organic anions. Among their unique characteristics, the potential to tune their physical and chemical properties by varying different features of the ILs, has led them being described as “designer solvents” [1, 2].

Cinnamic acid derivatives (CADs) are natural plant antioxidants. They occur in fruits, vegetables, spices, and aromatic herbs, and they are of particular interest due to their potential chemical and biological properties, such as antioxidant, free radical scavenging, anti-inflammatory, antimicrobial, anticarcinogenic, etc. They are used as raw materials for the synthesis of molecules with industrial interest, such as drugs, cosmetics and flavors, and in the preparation of resins and pharmaceutical products [3].

A prerequisite for the synthesis and design of chemical and separation processes is the reliable knowledge of the phase equilibrium behaviour of the systems involved. This work focuses on the solid-liquid equilibrium, i.e. solubility of solids in the liquid phase, of two CADs: p-coumaric and caffeic acid. Solubilities of these compounds have been measured in six imidazolium based ILs, having different anions and alkyl substitutes at the cation. The influence of the different anion, the length of the alkyl groups incorporated into the cation, the polarity and the ability of the IL to develop hydrogen bonding, on the solubility of the CADs is studied. The solubility data were successfully correlated with the NRTL and UNIQUAC local composition models.  Finally, the COSMO-RS model, which is a statistical thermodynamics approach based on the results of quantum chemical-COSMO calculations, is used for the prediction of the solubilities of the studied mixtures.

References
  1. M.G. Freire, L.M.N.B.F. Santos, A.M. Fernandes, J.A.P. Coutinho, I.M. Marrucho, Fluid Phase Equil, 261, 449 (2007)

  2. K.N. Marsh, J.A. Boxall, R. Lichtenthaler, Fluid Phase Equil. 219, 93 (2004).

  3. F.L. Mota, A.J. Queimada, S.P. Pinho, and E.A. Macedo, Ind. Eng. Chem. Res. 47, 5182 (2008).

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