Friedel-Crafts acylation reactions using metal triflates in ionic liquid

Aromatic electrophilic substitution reactions such as benzoylation and acetylation catalysed by metal triflates have been conducted in an ionic liquid, [bmim][BF4] (bmim = 1-butyl-3-methylimidazolium). Cu(OTf)(2) (OTf = trifluoromethanesulfonate) was found to be the most efficient catalyst used, affording quantitative conversion of benzoyl chloride and anisole to methoxybenzophenone within 1 h and with an ortho/para product ratio (o/p) of 4/96. The same reaction performed in the molecular solvents CH3CN and CH2ClCH2Cl gave lower 1 h conversions of 64 and 73%, respectively, and a reduced o/p regioselectivity of 7/93 in both cases. The scope and limitations of the reaction and recyclability of the ionic liquid/catalyst system are presented.