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Preparation of Second Generation Ionic Liquids by Efficient Solvent-Free Alkylation of N-Heterocycles with Chloroalkanes
Dipartimento di Scienza e Tecnologia del Farmaco, Università di Torino, Via Giuria 9, 10125 Torino, Italy
Laboratoire de Chimie Moléculaire et Environnement, Polytech’Savoie, Université de Savoie, 73376 Le Bourget du Lac Cedex, France
DSM Nutritional Products, Research and Development, NRD/CC, Building-214/071, P.O. Box 3255, CH 4002-Basel, Switzerland
* Author to whom correspondence should be addressed.
Received: 24 December 2007; in revised form: 23 January 2008 / Accepted: 23 January 2008 / Published: 25 January 2008
Abstract: Non-conventional techniques, such as microwave (MW) and power ultrasound(US) as well as combined MW/US irradiation, have been used to promote one-potsynthesis of second-generation ionic liquids (ILs), cutting down reaction times andimproving yields. However, the use of chloroalkanes in the alkylation of N-heterocyclesrequires more drastic conditions if results are to match those obtained with more reactivealkyl halides. The present paper describes a series of MW- or MW/US-promoted ILpreparations starting from chloroalkanes and classic heterocycles (1-methylimidazole,pyridine and 1-methylpyrrolidine). When reactions were carried out under conventionalheating in an oil bath they required longer reaction times and gave poorer yields. 1H-NMRanalysis and ion-exchange chromatography showed that the present solventless procedureafforded ILs of satisfactory purity. The observed high yields (usually 70-98% isolated),and short reaction times showed that a straightforward access to ILs can be also achievedwith the use of alkyl chlorides, resulting in a considerable reduction of costs.
Keywords: Ionic liquids; chloroalkanes; one-pot reaction; microwaves; ultrasound.
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Cravotto, G.; Gaudino, E.C.; Boffa, L.; Lévêque, J.-M.; Estager, J.; Bonrath, W. Preparation of Second Generation Ionic Liquids by Efficient Solvent-Free Alkylation of N-Heterocycles with Chloroalkanes. Molecules 2008, 13, 149-156.
Cravotto G, Gaudino EC, Boffa L, Lévêque J-M, Estager J, Bonrath W. Preparation of Second Generation Ionic Liquids by Efficient Solvent-Free Alkylation of N-Heterocycles with Chloroalkanes. Molecules. 2008; 13(1):149-156.
Cravotto, Giancarlo; Gaudino, Emanuela C.; Boffa, Luisa; Lévêque, Jean-Marc; Estager, Julien; Bonrath, Werner. 2008. "Preparation of Second Generation Ionic Liquids by Efficient Solvent-Free Alkylation of N-Heterocycles with Chloroalkanes." Molecules 13, no. 1: 149-156.