Application of activated bentonite impregnated with PdO as green catalyst for acylation reaction of aromatic compounds

Friedel-Crafts acylation reaction is a well-known reaction to synthesize acetophenone derivatives, which have a broad spectrum of bioactivity. However, Friedel-Crafts acylation mostly used acetyl chloride as a reagent with Lewis acid as a homogeneous catalyst, which is a nonenvironmental friendly process. In this work, a simple and efficient Friedel-Crafts acylation reaction is reported using the activated bentonite impregnated with PdO (PdOAB) as the heterogeneous catalyst. The PdOAB catalyst material was prepared through a two-steps reaction, i.e., an acid activation of natural bentonite and impregnation of palladium(II) nitrate under alkaline conditions. The optimum condition of the acetophenone synthesis was evaluated using the catalyst material by varying the catalyst mass and reaction time. The acetophenone derivatives with R = -H, -Cl, -CH3, -OCH3, -OH, and -NH2 at the para position were successfully synthesized from its corresponding aromatic compounds with glacial acetic acid in 86.6%, 7.9%, 91.7%, 86.6%, 82.7%, and 78.9% yield, respectively. From the experimental results, we proposed that the catalysis mechanism was mainly facilitated by the acid sites of the PdOAB catalyst material. The PdOAB catalyst material did not significantly lose its catalytic activity after four-cycle processes. Therefore, a green method for acetophenone synthesis was established because the byproduct is water, and the catalyst material can be recovered.