Brønsted acidic ionic liquid supported on rice husk ash (RHA-[pmim]HSO4): A highly efficient and reusable catalyst for the synthesis of 1-(benzothiazolylamino)phenylmethyl-2-naphthols

In this work, rice husk ash (RHA), as a natural source of amorphous silica, was used as a support for the immobilization of 1-methyl-3-(trimethoxysilylpropyl)-imidazolium hydrogen sulfate. The immobilized acidic ionic liquid was characterized with a variety of techniques, including infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and pH analysis. This reagent showed excellent catalytic activity for the preparation of 1-(benzothiazolylamino)phenylmethyl-2-naphthols from the one-pot condensation of an aldehyde, 2-aminobenzothiazole and 2-naphthol, at 100 °C under solvent-free conditions. The procedure gave the products in excellent yields in very short reaction times with high TOF. Also, this catalyst can be reused six times without loss of its catalytic activity.