Insights into the Mechanism of 2-Methylnaphthalene Friedel–Crafts Acetylation Catalyzed by AlCl3: A Combined Experimental and Theoretical Study

The Friedel–Crafts acetylation of 2-methylnaphthalene (2-MN) represents a powerful approach for synthesizing 2-methyl-6-acetylnaphthalene (2,6-MAN). The identification of catalytically active species in Friedel–Crafts acylation has recently attracted considerable attention. In this study, we performed an experimental and computational investigation of the AlCl3-catalyzed Friedel–Crafts acetylation of 2-MN in nitrobenzene and dichloromethane solvents. The yield of the acetylation can be significantly affected by the solvent and the addition method. Following the substitution mechanism, the stepwise deprotonation pathway is preferred in both solvents, which is mediated by the donor–acceptor complex as the catalytically active species. The calculations with the explicit solvent led to the same conclusions. This study provides important understanding of the AlCl3-catalyzed Friedel–Crafts acetylation reaction, with potential applications to other Lewis acid-catalyzed acylation reactions.