Abstract
Acid treatment of montmorillonite enhanced the acidity and also nanoporosity of the virgin clay. Montmorillonite clay was treated with p-TSA and HCl under microwave irradiation (MWI) and modified materials were characterized by BET, TPD-NH3 and FT-IR techniques. The activities of clays were studied for important condensation reactions such as the crossed aldol condensation and amide synthesis without solvent under MWI. Under conventional heating, maximum conversion was observed in 300 minutes while the same conversion was achieved in just 30 minutes under MWI. The activities of p-TSA treated clay were compared with HCl treated clays. The p-TSA treated clay showed surprisingly higher activity compared to other catalysts. The activity was attributed to the dealumination of structural Al and its migration to the interlayer region of the clay. The removal of Al made the material more nanoporous due to which accessibility to the acidic sites was better than the unmodified clay. Enhanced activity was due to higher amounts of interlayer aluminium in the p-TSA treated compared to HCl-treated ones. p-TSA treated clays retained their activity even after three subsequent runs in both the modes of heating. The catalyst used in the reaction rejuvenated by a simple procedure could be used for catalyzing the reaction again.
Keywords: Aldol condensation, dealumination, microwave irradiation, montmorillonite, solvent free reactions.
Graphical Abstract
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