Novel chiral ionic liquids: physicochemical properties and investigation of the internal rotameric behaviour in the neat system

Abstract

Optically active S-alkyl-N,N'-bis((S)-1-phenylethyl)thiouronium salts, abbreviated as (S)-[C(n)petu]Y (where Y is an anion; n = 1, 2, 3, 4, 6, 8, 10, 12 or 16), have been prepared and studied by a broad spectrum of analyses. This consists of density, viscosity, and conductivity determination, followed by a discussion of relevant correlations. Unusual trends depending on the S-alkyl chain length were documented for (S)-[C(n)petu][NTf2] series (where [NTf2](-) = bis{(trifluoromethyl)sulfonyl}amide), including the viscosity decreasing with increasing chain length, and the conductivity showing a maximum between the S-butyl and the S-hexyl derivative. In addition, a hindered rotamerism of the thiouronium cation in dmso-d6 solution was recognised by (1)H and (13)C NMR techniques. Thorough analysis of NMR spectra confirmed that the main contribution comes from rotation about the partial double C-S bond. For the first time, a neat thiouronium ionic liquid system has been subjected to quantitative analysis of hindered rotamerism by dynamic NMR coalescence studies, with estimated activation energy for rotation of 63.9 ± 0.4 kJ mol(-1). Finally, the application of (S)-[C(n)petu]Y salts as chiral discriminating agents for carboxylates by (1)H NMR spectroscopy was further investigated, demonstrating the influence of the S-alkyl chain length on chiral recognition; (S)-[C2petu][NTf2] ionic liquid with the mandelate anion gave the best results.

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

“…[18,19] Many examples such as cation variation by ether,[20,21] amide, nitrile,[22] alcohol, or alkene functionalization of the side chain but also chirality[23] have appeared in the literature. Amongst the several possibilities, fluorination has also been examined.…”

“…[7] Beside mixing, the interesting features of ILs can also be altered by their functionalization. [18,19] Many examples such as cation variation by ether, [20,21] amide, nitrile, [22] alcohol, or alkene functionalization of the side chain but also chirality [23] have appeared in the literature. Amongst the severalp ossibili-We present heret he possibility of formingt riphilic 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:p olar,l ipophilic, and fluorous ones.…”

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

“…For instance, the recently published pure shift experiments, 19,20 or J-resolved 21 , RES-TOCSY 22,10c and 1 H homonuclear decoupling experiment (HOMODEC) 23,24 techniques can be used for ee determinations in cases where the baseline resolution is insufficient for integration in the 1 H NMR spectra (see supporting information). In addition we inspected the possible enantiomeric resolution of three carboxylic acids (7,11,12) by using HSQC (2.0 mmol solution). Only in the case of 11 could resolution (6.15 Hz,0.049 ppm) be detected (see supporting information).…”

“…The enantiomeric resolution of neutral guests by ionic chiral solvating agents has rarely been studied, and when the guest is a carboxylic acid, it has usually been converted to the anion. [10][11][12][13] Mosher's acid was used as a test compound as it enables detection by both 1 H and 19 F NMR spectroscopy. In order to carry out a systematic study, the best performing chiral solvating agent was used in the resolution of seven different carboxylate salts, to establish its applicability in resolving both aromatic and non-aromatic racemic carboxylic acids.…”

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

“…47 These extraordinary and interesting features of RTILs conrm that the use of these RTILs in extensive selection of applications, particularly liquid range at high as well as low temperature can be utilized. Air exibility alterations were made by using known densities of resources.…”