Ordered mesoporous γ-Al2O3 as highly efficient and recyclable catalyst for the Knoevenagel reaction at room temperature

Coumarins are important class of organic compounds and intensively used in agricultural and pharmaceutical industries. We have developed a strategy for the synthesis of coumarin derivatives quantitatively via Knoevenagel condensation reaction of an ortho-hydroxyaryl aldehyde and an activated methylene compounds in the presence of ordered mesoporous gamma-Al2O3 as a heterogeneous catalyst. The catalyst has been thoroughly characterized through powder X-ray diffraction, N-2 sorption analysis, FTIR spectroscopy, TG/DTA, NH3-TPD and CO2-TPD (temperature programmed desorption) analysis. The material possesses periodicity in mesopores and both surface acidic and basic sites having strengths of 1.47 and 1.11 mmol g(-1), respectively, which is highly favorable for carrying out the Knoevenagel condensation reaction for the synthesis of a wide range of condensation product (yields similar to 98%) under very mild conditions. This amphoteric catalyst exhibits good surface Lewis acidity/basicity and high recyclability up to sixth reaction cycles without any significant loss in the product yield.