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

Magdalena B. Foreiter*, H. Q. Nimal Gunaratne, Peter Nockemann, Kenneth R. Seddon, Geetha Srinivasan

*Corresponding author for this work

Research output: Contribution to journalArticle

16 Citations (Scopus)

Abstract

Optically active S-alkyl-N, N'-bis((S)-1-phenylethyl) thiouronium salts, abbreviated as (S)-[Cnpetu] 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)-[Cnpetu][ 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-d(6) solution was recognised by H-1 and C-13 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 1H NMR spectroscopy was further investigated, demonstrating the influence of the S-alkyl chain length on chiral recognition; (S)-[C(2)petu][NTf2] ionic liquid with the mandelate anion gave the best results.

Original languageEnglish
Pages (from-to)1208-1226
Number of pages19
JournalPhysical Chemistry Chemical Physics
Volume16
Issue number3
Early online date28 Oct 2013
DOIs
Publication statusPublished - 21 Jan 2014

Keywords

  • NUCLEAR-MAGNETIC-RESONANCE
  • ISOTHIOURONIUM SALTS
  • PHYSICAL-PROPERTIES
  • CRYSTAL-STRUCTURE
  • TRIAZOLIUM SALTS
  • MOLTEN-SALTS
  • TEMPERATURE
  • SPECTROSCOPY
  • BOND
  • ORGANOCATALYSIS

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