Phosphomolybdic acid dispersed in the micropores of sulfate treated Zr-pillared clay as efficient heterogeneous catalyst for the synthesis of β-aminocarbonyl compounds in aqueous media

Abstract

Zr-pillared clay (Zr-P) was synthesized by insertion of zirconium oxyhydroxy clusters into clay interlayer and subsequent thermal activation. The Zr-P materials were treated with sulfuric acid to graft sulfate ions onto the zirconia nanopolliars. The sulfate grafted Zr-Pillared clay (SZr-P) was used as support for phosphomolybdic acid (PMA/SZr-P). The synthesized materials were characterized by XRD, IR, UV–Vis, SEM and sorptometric techniques. The expansion of the clay lattice as a result of pillaring was confirmed from X-ray diffraction study. The interlayer space was found to be retained in the PMA/SZr-P material. All pillared clay materials show Type-I sorption isotherm typical of microporous materials. The IR spectra of the pillared clay materials show the presence of acidic and non-acidic hydroxyl groups. The structural integrity of the phosphomolybdic acid in the clay matrix was ascertained from the IR and UV-Vis spectroscopy. The PMA/SZr-P material was used as an efficient catalyst for the one pot synthesis of β-aminocarbonyl compounds by Mannich reaction in aqueous media. The multicomponent condensation of aryl aldehyde, amines and ketones using PMA/SZr-P material afforded a variety of β-aminocarbonyl compounds in excellent yield and purity under ambient conditions. The protocol developed in this investigation using the PMA/SZr-P material was found to be advantageous in terms of simple experimentation, preclusion of toxic solvents, recyclable catalyst and high yield and purity of the products.