Solvent free selective acylation of phenol by HF–modified saponite catalysts

The preparation and characterization of hydrofluoric acid (HF)–modified saponite catalysts and their application in the selective synthesis of 4–hydroxyacetophenone through acylation reaction is reported. This method is solvent–free and would be effectively scaled up for the selective preparation of the para–isomer product. The prepared 4–hydroxyacetophenone was characterized by ¹H and ¹³C NMR, FT–IR, and UV–Visible spectroscopic techniques. The experimental conditions were milder than in conventional methods and gave excellent yields using low amounts of acid–treated catalysts, which were found to be superior to other catalysts for this particular reaction. The catalysts were found to be environmentally benign, cost-effective, and recyclable over three cycles without appreciable loss in activity. The reaction seemed to be controlled by the Lewis acidity and the porosity of treated saponite, and thus this work opens a new strategy for the use of clay minerals as catalysts in Fine Chemistry reactions.