Greener synthesis of new ammonium ionic liquids and their potential as extracting agents Daniel Kogelnig * , Anja Stojanovic, Markus Galanski, Michael Groessl, Franz Jirsa, Regina Krachler, Bernhard K. Keppler University of Vienna, Institute of Inorganic Chemistry, Waehringer Strasse 42, 1090 Vienna, Austria Received 24 January 2008; revised 19 February 2008; accepted 22 February 2008 Available online 29 February 2008 Abstract New hydrophobic ionic liquids were synthesized from tricaprylmethylammonium chloride (Aliquat 336 Ó ) and selected Bronsted acids by a sustainable, simple and cost-saving deprotonation-metathesis route. Prepared ionic liquids were evaluated as potential extracting agents for cadmium from different aqueous solutions. High efficiency and selectivity were reached for the extraction of cadmium from a natural river matrix with tricaprylmethylammonium thiosalicylate, [A336][TS], a thiol-containing task specific ionic liquid. Ó 2008 Elsevier Ltd. All rights reserved. The synthesis of ionic liquids (ILs), their characteriza- tion, and possible applications have been developing pro- gressively, as the properties of this class of organic salts with melting points below the boiling point of water have gained intensive attention in nearly all fields of chemistry. Furthermore, through the incorporation of functional groups, the synthesis of task specific ILs (TSILs) has been a focus of research, leading to tailor-made substances for desired applications. 1 A widespread research field is the use of ILs as well as TSILs incorporating disulfide-, thioether-, urea- or hydroxybenzylamine groups as extracting agents for met- als. 2–7 Most of ILs or TSILs for extracting applications described in the literature are based on imidazolium-, pipe- ridinium-, pyrrolidinium- and pyridinium cations and fluo- rine containing anions, whereas diverse functional groups are generally appended to the cation. 3–7 In contrast, the newly synthesized ILs described here are based on a hydro- phobic, long chain tetraalkylammonium cation with ali- phatic and aromatic carboxylate anions. Furthermore, tricaprylmethylammonium thiosalicylate, [A336][TS], pos- sesses a thiol-containing anion. New ammonium ILs were prepared by stirring equimo- lar amounts of Aliquat 336 Ó as a precursor and selected Bronsted acids in a sodium hydroxide solution. Deproto- nation of the acid followed by anion metathesis led to the desired ionic liquids (Scheme 1). Aliquat 336 Ó is actually an ionic liquid itself and is regarded as a 2:1 mixture of methyl trioctylammonium- and methyl tridecylammonium chloride with a proposed mean molar weight of 432 g/mol. 8 We investigated the structure of the Aliquat 336 Ó -cation and positive ion mode electrospray ioniza- tion-mass spectrometry (ESI-MS) disclosed peaks that could be assigned to methyl tricapryl cations containing either octyl- or decylchains or mixtures of them. However, one peak could clearly be assigned to an existing methyl 0040-4039/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2008.02.138 * Corresponding author. Tel.: +43 1 4277 52626; fax: +43 1 4277 52620. E-mail address: daniel.kogelnig@univie.ac.at (D. Kogelnig). Scheme 1. Synthesis of tricaprylmethylammonium based ionic liquids. Available online at www.sciencedirect.com Tetrahedron Letters 49 (2008) 2782–2785