Acid treatment of halloysite nanoclay: Eco-friendly heterogeneous catalyst for the synthesis of pyrrole derivatives

Halloysite is a two-layered aluminosilicate with a tube structure. The external surface and the internal of halloysite nanotubes (HNTs) are composed of silicon-oxygen tetrahedron and alumina oxygen octahedrons, respectively. The reaction of the acid with both the outer and inner surfaces of the nanotubes causes the AlO₆ octahedral layers to dissolve and dealumination occurred. The acid treatment of halloysite has been used as a traditional chemical activation method for improving the performance of its catalytic activity. In continues to our research and due to the importance of pyrrole scaffold, herein, an efficient synthesis of pyrrole derivatives was carried out in the presence of a catalytic amount of acid treatment HNTs as a nanocatalyst in ethanol at room temperature in high yields. The solid nanocatalyst can be recovered easily and reused without any significant loss of the catalytic activity.