Brönsted acidic ionic liquid supported on rice husk ash (RHA–[pmim]HSO4): a highly efficient and reusable catalyst for the formylation of amines and alcohols

Abstract

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. The catalytic performance of this heterogeneous ionic liquid was probed for the N-formylation of a variety of amines using formic acid under solvent free conditions. It is also useful for the formylation of benzylic alcohols. The procedure gave the products in excellent yields in very short reaction times. Also this catalyst can be reused ten times without loss of its catalytic activity.