Preparation of second generation ionic liquids by efficient solvent-free alkylation of N-heterocycles with chloroalkanes

Molecules. 2008 Jan 25;13(1):149-56. doi: 10.3390/molecules13010149.

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-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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alkylation
  • Chlorine Compounds / chemistry*
  • Heterocyclic Compounds / chemistry*
  • Ionic Liquids / chemical synthesis*
  • Microwaves
  • Solvents / chemistry*
  • Ultrasonics

Substances

  • Chlorine Compounds
  • Heterocyclic Compounds
  • Ionic Liquids
  • Solvents