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.
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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.