Ephedrinium‐based protic chiral ionic liquids for enantiomeric recognition

Abstract

We report the synthesis of a series of novel structurally related protic chiral ionic liquids (PCILs) derived from ephedrines. Enantiopure norephedrine, ephedrine, and methylephedrine were neutralized by use of fluorinated acids, bis(trifluoromethanesulfonyl)imide, and bis(pentafluoroethanesulfonyl)imide to afford six PCILs with protonated primary, secondary, and tertiary amines. The goal of this study is to investigate the influence of structure on both chiral recognition abilities and physicochemical properties of these closely related PCILs. The newly synthesized PCILs were characterized by use of nuclear magnetic resonance (NMR), thermal gravimetric analysis, differential scanning calorimetry, circular dichroism (CD), mass spectrometry, and elemental analysis. The PCILs were thermally stable up to 220°C and had glass transition temperatures between -60 and -30°C. Both enantiomers of the PCILs retained chirality throughout the synthesis as demonstrated by use of CD measurements. More interestingly, these ephedrinium PCILs displayed strong chiral recognition capabilities as evidenced by peak splitting of the chemical shift of the trifluoro group of potassium Mosher's salt by use of (19)F-NMR. In addition, these PCILs demonstrated enantiomeric recognition capabilities toward a range of structurally diverse analytes using steady-state fluorescence spectroscopy.

Synthesis and Characterization of a Glycine‐L‐Histidine‐Based Chiral Ionic Liquid and Enantioselectivity Evaluation by Fluorescence Spectroscopy

“…Other highly fluorescent ephedrinium and amino acid based ILs were described by Warner and coworkers. [20,40,41] In these studies, the ephedrinium and amino acid based ILs were used as solvents and selectors in fluorescence spectroscopic chiral recognition investigations. Recently, fluorescence spectroscopy was reported in enantiomeric recognition by a nicotine based CILs.…”

Group of Uniform Materials Based on Organic Salts (GUMBOS): A Review of Their Solid State Properties and Applications

“…In fact, the literature on development of novel methodologies based on use of ionic liquids (ILs), a group of uniform materials based on organic salts (GUMBOS), and nanoGUMBOS is increasing at an ever-expanding rate. For example, numerous studies from the literature can be cited for utility of such materials in diverse areas such as antibiotics [13][14][15], cancer therapy [16][17][18][19][20][21][22][23][24], hydrogels [25,26], cellular imaging [27,28], chirality [29][30][31][32][33], dye-sensitized solar cells (DSSCs) [34][35][36], extractions [37][38][39], gel electrophoresis [40,41], detection of reactive oxygen species [42], liquid crystals [43], mass spectrometry [44], nanomaterials [45][46][47][48][49][50][51][52], optoelectronics [53][54][55][56], sensors [57]…”

Synthesis of Tertiary and Quaternary Amine Derivatives from Wood Resin as Chiral NMR Solvating Agents

“…With 4 being readily soluble in CDCl 3 , unlike its potassium or sodium salt, this modification obviates the use of solubilizing additives such as crown ethers [16]. We also report a modification of the RES-TOCSY 2D-NMR technique to enhance enantiomeric discrimination when the resolution of multiplets is insufficient for ee determination.…”