The "kinetic capture" of an acylium ion from live aluminum chloride promoted Friedel-Crafts acylation reactions.

AlCl(3) promoted Friedel-Crafts acylation between 4-tert-butylbenzoyl chloride and mesitylene was investigated. The donor-acceptor complex was observed as the major species. Kinetic investigation demonstrated that the reaction was first-order on the donor-acceptor complex and zero-order on ArH, suggesting that the donor-acceptor complex was not the true reactive species. However, the acylium ion was almost invisible with a fairly low concentration under live reaction conditions. It was approved as the true reactive species through kinetic data ("kinetic capture") in the AlCl(3) promoted Friedel-Crafts acylation reaction.