Microwave assisted synthesis of fine chemicals in solvent-free conditions over mesoporous zirconium phosphate

Abstract

Synthesis of various industrially important fine chemicals under microwave irradiation (MWI) in solvent-free conditions over mesoporous zirconium phosphate (m-ZrP) is reported. m-ZrP is synthesized by MWI in basic medium using a precursor solution of zirconium carbonate complex as zirconium source and CTAB as a pore-directing agent. MWI time and MWI power were found to have significant influence on the textural properties of synthesized m-ZrP. Microscopic analyses of the synthesized m-ZrP indicate the presence of worm like pores with spherical morphology. DRIFT analysis of pyridine adsorbed m-ZrP and NH3-TPD measurements indicate the presence of appreciable amount of Brönsted acid sites. Synthesized m-ZrP exhibits high catalytic activity towards Claisen–Schmidt condensation reaction in solvent-free conditions under microwave irradiation. The m-ZrP showed high activity towards other acid catalyzed reactions such as Friedel–Craft benzylation, Pechmann condensation and carbonyl group protection reaction, and also for the synthesis of benzo-xanthenes in solvent-free conditions under MWI. The catalytic activity of m-ZrP is substantially higher than that of conventional layered ZrP. The synthesized catalysts are re-usable for at least five times after regeneration, without losing their catalytic activity significantly.