The first unequivocal evidence of the reacting electrophile in aromatic acylation reactions

The acylation of aromatic compounds with aroyl triflates can be performed in organic solvents (1,2-dichloroethane) without Friedel-Crafts catalysts. These reaction conditions allow kinetic investigations of the reaction in homogeneous solution. From rate measurements evidence is given that in all cases the aroyl triflates 1, 6, and 11 dissociate primarily into the corresponding acylium ions which subsequently react with the aromatic compounds. The rate-determining step, either the dissociation of the aroyl triflates or the reaction of the acylium ions with the aromatic, can be assigned definitely from the experimental data. From the kinetic measurements in the presence of an excess of base unequivocal evidence of acylium ions as the reacting electrophiles in all cases investigated is given.