Chiral ionic liquid crystals based on thiourea

Chiral ionic liquid crystals based on the S-methyl-N,N′-α-methylarylthiouronium cation have been prepared and studied.

Enantioseparation by Capillary Electrophoresis Using Ionic Liquids as Chiral Selectors

Capillary electrophoresis (CE) is one of the most widely employed analytical techniques to achieve enantiomeric separations. In spite of the fact that there are many chiral selectors commercially available to perform enantioseparations by CE, one of the most relevant topics in this field is the search for new selectors capable of providing high enantiomeric resolutions. Chiral ionic liquids (CILs) have interesting characteristics conferring them a high potential in chiral separations although only some of them are commercially available. The aim of this article is to review all the works published on the use of CILs as chiral selectors in the development of enantioselective methodologies by CE, covering the period from 2006 (when the first research work on this topic was published) to 2017. The use of CILs as sole chiral selectors, as chiral selectors in dual systems or as chiral ligands will be considered. This review also provides detailed analytical information on the experimental conditions used to carry out enantioseparations in different fields as well as on the separation mechanism involved.

Chiral protic imidazolium salts with a (-)-menthol fragment in the cation: synthesis, properties and use in the Diels-Alder reaction

New chiral protic imidazolium salts containing a (1R,2S,5R)-(-)-menthol substituent in the cation and four different anions (chloride, hexafluorophosphate, trifluoromethanesulfonate and bis(trifluoromethylsulfonyl)imide) were efficiently prepared and extensively characterized. Detailed NMR analysis was performed, and a comparison of the chemical shifts of the protons and carbons of the imidazolium cation as a function of the combined anion was discussed. The specific rotation, solubility in commonly used solvents, thermal properties including phase transition temperatures, and thermal stability were also determined. Three of the synthesized tertiary salts (Cl, PF6 or OTf anion) were crystalline solids; 1-H-3-[(1R,2S,5R)-(-)-menthoxymethyl]-imidazolium bis(trifluoromethylsulfonyl)imide, (-)[H-Ment-Im][NTf2] was a liquid at room temperature. The chiral protic salts were used in a Diels-Alder reaction as a test reaction, and the results were compared with those from aprotic chiral ionic liquids having the same chiral substituent in the cation (1R,2S,5R)-(-)-menthol with a bis(trifluoromethylsulfonyl)imide anion. Both protic and aprotic chiral salts, used in a Diels-Alder reaction, were pure (-)-enantiomers, which was determined by NMR with Δ-TRISPHAT tetrabutylammonium salt as a chiral shift reagent. Protic salts offered distinctly higher endo/exo ratios than aprotic ones, but an enantiomeric excess was not obtained. The stereoselectivity reached the same high level even after the fourth recycle of (-)[H-Ment-Im][NTf2] in the reaction of ethyl-vinyl ketone with cyclopentadiene at temperature of -35 °C.

1-(+)-Dehydroabietylimidazolium Salts as Enantiomer Discriminators for NMR Spectroscopy

Nine new (+)-dehydroabietylimidazolium salts were synthesised and studied as chiral solvating agents for several different racemic aromatic and non-aromatic carboxylate salts. These cationic chiral solvating agents resolve racemic ionic analytes better than non-ionic ones. Bis(dehydroabietylimidazolium) bis(trifluoromethanesulfonimide) gave the best discrimination for the enantiomers of carboxylate salts. Its resolution behaviour was studied by an NMR titration experiment, which indicated 1 : 1 complexation with the racemic analyte. The dehydroabietylimidazolium salts were also useful in enantiomeric excess (ee) determinations, and for the recognition of chirality of racemic aromatic and non-aromatic α-substituted carboxylic acids.

Arrangements of enantiopure and racemic ionic liquids at the liquid/air interface: the role of chirality on self-assembly and layering

This paper reports on the self-assembly ability at the interface IL/air for some couples of enantiopure and racemic chiral ILs.

Triphilic Ionic-Liquid Mixtures: Fluorinated and Non-fluorinated Aprotic Ionic-Liquid Mixtures

We present here the possibility of forming triphilic mixtures from alkyl- and fluoroalkylimidazolium ionic liquids, thus, macroscopically homogeneous mixtures for which instead of the often observed two domains-polar and nonpolar-three stable microphases are present: polar, lipophilic, and fluorous ones. The fluorinated side chains of the cations indeed self-associate and form domains that are segregated from those of the polar and alkyl domains. To enable miscibility, despite the generally preferred macroscopic separation between fluorous and alkyl moieties, the importance of strong hydrogen bonding is shown. As the long-range structure in the alkyl and fluoroalkyl domains is dependent on the composition of the liquid, we propose that the heterogeneous, triphilic structure can be easily tuned by the molar ratio of the components. We believe that further development may allow the design of switchable, smart liquids that change their properties in a predictable way according to their composition or even their environment.

Esterification of carboxylic acids with alkyl halides using imidazolium based dicationic ionic liquids containing bis-trifluoromethane sulfonimide anions at room temperature

Task-specific RTILs of symmetrical N-methylimidazolium rings linked to an oligo (ethylene glycol) chain (cationic part) and bis-trifluoromethane sulfonimide (anionic part) were synthesized, and the physicochemical properties with catalytic activity were determined.