Ionic liquids as recyclable reaction media for the tetrahydropyranylation of alcohols

A comparative study of the catalysed tetrahydropyranylation of 1-phenyletha nol by p-toluenesulphonic acid (TsOH), pyridinium p-toluenesulphonate (PPTS ) and triphenylphosphine hydrobromide (TPP.HBr) using 3,4-dihydro-2H-pyran in dichloromethane or in the ionic liquids 1-n-butyl-3-methylimidazolium te trafluoroborate ([bmim][BF4]) or 1-n-butyl-3-methylimidazolium hexafluoroph osphate ([bmim][PF6]) showed that the reaction occurs readily in [bmim][PF6 ] for PPTS or TPP.HBr by a non-reversible process. These reaction media wer e recycled on 22 occasions without loss of activity and their scope of appl ication to other alcohols was also studied. (C) 2001 Elsevier Science Ltd. All rights reserved.