The Friedel-Crafts acylation of substituted benzenes proceeds smoothly by using a catalytic amount of a lanthanide trifluoromethanesulfonate [Ln(OTf),], which is easily recovered from the reaction mixture and reused without a decrease in catalytic activity.

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Lithium perchlorate is found to accelerate Ln(OTQ3-catalysed Friedel-Crafts acylation; the catalytic system, Ln(OTf)3-LiC104, is easily recovered from the reaction mixture by simple extraction and can be reused without decrease in its catalytic activity.

Rare earth metal trifluoromethanesulfonates (rare earth metal triflates, RE(OTf)3) were found to be efficient catalysts for Friedel-Crafts acylation and alkylation. In the presence of a catalytic amount of RE(OTf)3, acylation of aromatic compounds having electron-donating substituents such as anisole, thioanisole, and mesitylene with acid anhydrides proceeded smoothly to afford the corresponding aromatic ketones in high yields. Although RE(OTf)3 alone is not effective for acylation of less reactive aromatics such as toluene, the combination of RE(OTf)3 and lithium perchlorate (LiClO4) enhanced the catalytic activity dramatically. Friedel-Crafts acylation reactions using rare earth metal perfluoroalkanesulfonates were also successfully performed in supercritical carbon dioxide (scCO2). Moreover, in the presence of a catalytic amount of RE(OTf)3, aromatic compounds reacted with benzyl chloride smoothly to afford the corresponding alkylation products in high yields. In these reactions, RE(OTf)3 could be easily recovered after the reactions were completed and could be reused without loss of activity.