Fly ash supported scandium triflate as an active recyclable solid acid catalyst for Friedel-Crafts acylation reaction

Coal generated fly ash is converted into an efficient solid Lewis acid catalyst by loading scandium triflate on thermally and chemically activated fly ash. The activation of fly ash increased the surface silanol groups responsible for loading of scandium triflate species on fly ash surface. The physico-chemical properties of prepared fly ash supported scandium triflate (FST) catalyst were examined by XRD, FTIR, TEM and TGA analysis. The proposed model structure of FST shows that the triflate species withdraws the electron density from the scandium resulting in generating electron deficient Lewis acid sites on fly ash surface as confirmed by NH3 adsorbed FT-IR spectrum of FST catalyst. The catalyst showed higher activity for solvent free single pot Friedel-Crafts acylation of 2-methoxynaphthalene (2-MN) using acetic anhydride as an acylating agent achieving conversion up to 84% and selectivity of the desired product, 2-acetyle-6-methoxynaphthalene (6-AMN) up to 73%. 6-AMN is a precursor for anti-inflammatory drug, (S)-(+)-6-mathoxy-α-methyl-2-naphthaleneacetic acid, known as Naproxen. The stability of the catalyst was confirmed by hot filtration test. The catalyst could be easily regenerated and reused giving similar conversion up to three reaction cycles under similar experimental conditions. The work reports an alternative pathway for utilization of waste fly ash by using it in developing novel and cost effective, recyclable catalyst system for industrially important acylation reactions.