A number of ionic liquids have been used as co-solvents for the N-alkyl-3,4-dihyroisoquinoliunium catalyzed epoxidation of alkenes. Water miscible ionic liquids gave systems with similar reactivities to the conventional acetonitrile based systems. Attempts to produce an aqueous/ionic liquid biphasic system that could be used to recycle the catalyst failed due to a lack of phase transfer between the aqueous and ionic liquid phases. (c) 2007 Elsevier B.V. All rights reserved.