A Comparative Study on Catalytic Activity of Solid Acid Catalysts towards Microwave Assisted Synthesis of Coumarin Derivatives

In the present endeavour, coumarin derivatives have been synthesized replacing the conventional catalyst with environment friendly solid acid catalysts. Two types of catalysts possessing similar elemental composition have been explored for their potential utility as solid acid catalyst. M (IV) Phosphotungstates which possess inherent acidity have been synthesized by sol-gel route, while in another case, acidity has been induced into M (IV) oxides, by process of anchoring and calcination, using 12-Tungstophosphoric acid (12-TPA) [M (IV) = Ti and Sn]. All the catalysts have been characterized for elemental analysis by ICP-AES, TGA, FTIR, SEM, EDX, XRD, surface area (by BET method) and surface acidity (by NH3-TPD method). The performance of these materials as solid acid catalysts has been explored by studying Pechmann condensation as a model reaction, wherein various phenols have been treated with methyl acetoacetate to give coumarins, under solvent free conditions using conventional and microwave heating. The synthesis conditions have been optimized by varying parameters such as reaction temperature, reaction time, catalyst amount and mole ratio of the reactants. The catalytic activity of synthesized materials has been compared and correlated with acid properties of the materials.