RESEARCH FRONT CSIRO PUBLISHING Communication Aust. J. Chem. 2007, 60, 64–67 www.publish.csiro.au/journals/ajc Facile Synthesis of a Chiral Ionic Liquid Derived from 1-Phenylethylamine Syed A. Ashraf, A Yingpit Pornputtkul, A Leon A. P. Kane-Maguire, A and Gordon G. Wallace A,B A ARC Centre for Nanostructured Electromaterials, Intelligent Polymer Research Institute, University of Wollongong, Wollongong NSW 2522, Australia. B Corresponding author. Email: gwallace@uow.edu.au A simple route is described to enantiomerically pure ionic liquids derived from (+)- and (−)-1-phenylethylamine. These very low melting point (−42 ◦ C) ionic liquids, containing the bis(trifluoromethylsulfonylimide) anion, possess a wide electrochemical potential window between −2.0 and +2.0V (versus Ag|AgCl). They show chiral discrimination between the enantiomeric forms of Mosher’s salt, suggesting their potential as media for electrochemical asymmetric syntheses or chiral chromatography. Manuscript received: 17 October 2006. Final version: 19 December 2006. Room-temperature ionic liquids (ILs) have attracted much recent interest as novel solvents and electrolytes for chemical and electrochemical synthesis, catalysis, and battery applications because of their remarkable properties such as high ionic con- ductivity, wide electrochemical potential window, low volatility, good chemical and thermal stability, and ability to dissolve a wide range of organic and inorganic species. [1] These proper- ties have led them to being championed as ‘green solvents’ for a range of chemical processes. [2,3] The electrochemical stability of inherently conducting organic polymers can also be markedly enhanced in ionic liquids, with negligible degradation being reported [4–7] even after extensive electrochemical switching. There have been few reports to date of chiral ionic liquids, despite their potential applications in asymmetric synthesis and chiral separations. As detailed in an excellent recent review, [8] the source of the chirality in such electrolytes may reside either in the cationic moiety (e.g. chiral imidazolium, [9–11] N- methylephedrinium, [12] and substituted oxazolinium [12] cations) or the counter anion (e.g. camphor sulfonate [13] ). As part of a pro- gramme exploring electrochemical asymmetric synthesis as an alternative to the more conventional chemical routes to homochi- ral chemicals, we desired access to an inexpensive chiral ionic liquid that could be employed over a wide temperature range (<0 to >50 ◦ C), possessed a wide electrochemical potential window (covering at least the range −1.5 to +1.5 V versus Ag|AgCl) and good electrical conductivity, and could be prepared in high opti- cal purity, via a minimum number of steps, from readily available starting materials. We report here the facile synthesis of the two enantiomerically pure forms of a novel chiral ionic liquid, based on the 1-phenylethylammonium cation, that meet these criteria. The new ionic liquids (S)-(−)-N-ethyl-1-phenylethylammo- nium bis(trifluoromethylsulfonylimide) 2a and its enantiomer 2b were prepared via two simple steps from the readily avail- able optically active (S)-(−)- and (R)-(+)-1-phenylethylamine (PhEA; Scheme 1). Quaternization of the chiral amine precur- sors with ethyl bromide proceeded smoothly in DMF solvent Scheme 1. at 0–5 ◦ C to give the crystalline ammonium salts 1a and 1b in 53% yield. Their 1 H NMR spectra in D 2 O (see below) con- firmed mono-ethylation of the nitrogen centre, as did their positive ion electrospray mass spectra (ESMS; m/z 150 (M + )) and elemental analyses. A subsequent metathesis reaction between aqueous solutions of these bromide salts and lithium bis(trifluoromethylsulfonylimide) (LiTf 2 N) led to the formation of two liquid phases: The upper aqueous layer contained LiBr product while the lower, more dense (s.g. 1.45) layer was the desired ionic liquids [C 6 H 5 CH(Me)NH 2 Et](Tf 2 N) 2. The pres- ence of the highly hydrophobic Tf 2 N − anion in 2 is presumably responsible for their immiscibility in water, permitting this facile separation. The ionic liquids were washed with water to remove possible contamination with LiBr and dried by passing through a stream of dinitrogen gas while heating at 70 ◦ C (yield 75%). Scale-up to the synthesis of 100 g quantities of the enantiomeric ionic liquids 2a and 2b was readily achieved. The structure of the new, chiral ionic liquids 2a and 2b was confirmed from their 1 H NMR spectra, ESMS, and optical rota- tion/circular dichroism (CD) spectra. Their 1 H NMR spectra © CSIRO 2007 10.1071/CH06384 0004-9425/07/010064