Solvent free synthesis of coumarins using environment friendly solid acid catalysts

Solid acid catalysts, ZrPW (Zirconium(IV) Phosphotungstate) and 12-TPA/ZrO2 [12-Tungstophosphoric acid (12-TPA) supported onto ZrO2] have been synthesized. The catalysts have been characterized for chemical stability, elemental analysis by ICP-AES, TGA, FTIR, SEM, EDX, XRD, surface area (BET) and surface acidity (NH3-TPD). The performance of these materials as solid acid catalysts has been explored by studying Pechmann condensation as a model reaction, wherein phenols have been treated with methyl acetoacetate to give coumarins, under solvent free conditions using conventional heating as well as microwave heating. Catalytic activity of both the solid acid catalysts have been compared and correlated with surface properties of the materials.

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► ZrPW(Zirconium(IV)Phosphotungstate) is used as solid acid catalyst for the first time.
► 12TPA/ZrO2 (12Tungstophosphoric acid supported onto ZrO2) is used for comparison.
► ZrPW, 12TPA/ZrO2 are solid acids possessing inherent and induced acidity respectively.
► ZrPW, 12TPA/ZrO2 have been explored as catalysts in solvent free coumarin synthesis.
► Coumarin synthesis has been performed under conventional and microwave heating.