Solvent-Free Friedel-Crafts Acylation of Fluorobenzene Catalyzed by Trifluoromethanesulfonic Acid and Rare Earth Triflates

Abstract

Solvent-free Friedel-Crafts acylation of fluorobenzene with benzoyl chloride was investigated over the trifluoro- methanesulfonic acid (TfOH) and rare earth triflate (Re(OTf)3) composite catalyst. The results showed that the presence of Re(OTf)3 leads to the decrease in a half amount of TfOH catalyst, and there is a synergistic effect between TfOH and Re(OTf)3 in this composite catalyst. For the solvent-free acylation of fluorobenzene with benzoyl chloride, the catalytic activities of 11 kinds of rare earth elements Re(OTf)3 were tested, and it was found that among all Re(OTf)3 compounds La(OTf)3 exhibits the best catalytic performance and it can be repeatedly used. After the acylation of fluorobenzene with benzoyl chloride over the La(OTf)3 and TfOH catalyst at 140 ℃ for 4 h, the selectivity and yield to para-product fluorobenzophenone reach up to 99% and 87%, respectively. For the acylation of different benzene derivatives with benzoyl chloride over the TfOH and Re(OTf)3 catalyst, the promoting catalysis of different elements Re(OTf)3 is different, for instance, for the acylation of dimethylbenzene, Ce(OTf)3 exhibits the best catalytic performance among the tested Re(OTf)3 promoters. Keywords Trifluoromethanesulfonic acid and rare earth triflate; Fuorobenzene; Benzoyl chloride; Friedel-Crafts acylation; Composite catalyst system.