Solid Acid Catalysts for Coumarin Synthesis by the Pechmann Reaction: MOFs versus Zeolites

The catalytic behavior of metalorganic frameworks Cu-benzene-1,3,5-tricarboxylate (CuBTC) and Fe-benzene-1,3,5-tricarboxylate (FeBTC) was investigated in the Pechmann condensation of different phenols (resorcinol, pyrogallol, and naphthol) with ethyl acetoacetate and compared with large-pore zeolites beta (BEA) and ultrastableY (USY). Zeolites BEA and USY exhibited high activity in transformations of the most active substrates (resorcinol and pyrogallol) but a low conversion of naphthol was observed. Almost total transformation of naphthol (9498% conversion) to the target product was achieved within 24h of the reaction time over CuBTC and FeBTC. We assume that the regularity in the arrangement of active sites within the framework of CuBTC, which results in the existence of 2 active centers in close proximity, is of critical importance to the transformation of naphthol in the Pechmann reaction that leads to coumarin.