Synthesis and evaluation of l-phenylalanine ester-based chiral ionic liquids for GC stationary phase ability

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Several l-phenylalanine alkyl ester-based cations formed ionic liquids after coupling with bis-(perfluoroethylsulfonyl) imide ([(C2F5SO2)2N]) and bis-(trifluoromethanesulfonyl) amide ([(CF3SO2)2N]). The relationship between the structure of l-phenylalanine alkyl ester cations and perfluorinated anions and properties of subsequently synthesized chiral ionic liquids was investigated. The ionic liquids were obtained in good yields and were liquid at room temperature. The ionic liquids having a methyl and ethyl substituent on the cation unit exhibited the highest thermal decomposition temperatures that ranged from 280 °C to 296 °C among the synthesized ionic liquids. These ionic liquids displayed the lowest glass transition temperatures of between − 45 °C to − 51 °C. The introduction of a different alkyl substituents on the cation caused the melting point and viscosity of the ionic liquids to vary slightly. Ionic liquids based on the [(C2F5SO2)2N] anion presented higher melting points than those based on the [(CF3SO2)2N] anion, for each corresponding cation. The neat chiral ionic liquids showed different fluorescence spectral behavior when excited at the same wavelength. Steady-state fluorescence spectroscopic measurements revealed the chiral discrimination of l-Phenylalanine ethyl ester bis-(perfluoroethylsulfonyl) imide for pure enantiomers of 2,2,2-trifluoroanthryl ethanol.


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