Preparation of second generation ionic liquids by efficient solvent-free alkylation of N-heterocycles with chloroalkanes.
Non-conventional techniques, such as microwave (MW) and power ultrasound (US) as well as combined MW/US irradiation, have been used to promote one-pot synthesis of second-generation ionic liquids (ILs), cutting down reaction times and improving yields. However, the use of chloroalkanes in the alkylation of N-heterocycles requires more drastic conditions if results are to match those obtained with more reactive alkyl halides. The present paper describes a series of MW- or MW/US-promoted IL preparations starting from chloroalkanes and classic heterocycles (1-methylimidazole, pyridine and 1-methylpyrrolidine). When reactions were carried out under conventional heating in an oil bath they required longer reaction times and gave poorer yields. (1)H-NMR analysis and ion-exchange chromatography showed that the present solventless procedure afforded 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 achieved with the use of alkyl chlorides, resulting in a considerable reduction of costs.
Cravotto
Giancarlo
G
Dipartimento di Scienza e Tecnologia del Farmaco, Università di Torino, Via Giuria 9, 10125 Torino, Italy. giancarlo.cravotto@unito.it
Gaudino
Emanuela Calcio
EC
Boffa
Luisa
L
Lévêque
Jean-Marc
JM
Estager
Julien
J
Bonrath
Werner
W
D000478:Alkylation; D017606:Chlorine Compounds / Q000737:chemistry*; D006571:Heterocyclic Compounds / Q000737:chemistry*; D052578:Ionic Liquids / Q000138:chemical synthesis*; D008872:Microwaves; D012997:Solvents / Q000737:chemistry*; D014465:Ultrasonics
D017606:Chlorine Compounds; D006571:Heterocyclic Compounds; D052578:Ionic Liquids; D012997:Solvents