Propylsulfonic acid grafted on mesoporous siliceous FDU-5 material: A high TOF catalyst for the synthesis of coumarins via Pechmann condensation

Coumarins and their synthetic derivatives are extensively used as base chemicals in diverse industrial applications in the fields of pharmaceutics, cosmetics, and agrochemicals, among others. Due to the growing number of applications, the need for new methods of coumarins synthesis has gained importance worldwide. In this sense, the use of propylsulfonic acid supported in FDU-5 (FDU-5-Pr-SO3H) as a catalyst for the synthesis of coumarins via Pechmann condensation in solvent free medium was investigated. FDU-5-Pr-SO3H was synthesized by co-condensation of MPTES and TEOS. FDU-5-Pr-SO3H was used as catalyst for the synthesis of 7-hydroxy-4-methylcoumarin and reaction conditions were optimized. The optimization process involved the study of the influence of the catalyst load, Resorcinol:EAA molar ratio, reaction temperature and reaction time. The optimal conditions were: catalyst load of 1.65 mol %, reactants molar ratio of 1:1.5, temperature 130 degrees C and 60 min of reaction time. Under these conditions, the FDU-5-Pr-SO3H material showed excellent yield (96.5%) and turn over frequency (59 h(-1)). Finally, the synthetized material was assessed as a catalyst with other phenolic compounds with ethyl acetoacetate and with ethyl benzoylacetate. The obtained products were isolated and identified by comparison of their spectral data with those reported in literature; from these results can be concluded that the catalyst is active with a wide range of phenolic substrates.