Comparison of the catalytic activity of MOFs and zeolites in Knoevenagel condensation

The catalytic behavior of metal-organic-frameworks (MOFs) CuBTC and FeBTC was investigated in Knoevenagel condensation of cyclohexane carbaldehyde and benzaldehyde with active methylene compounds and compared with zeolites BEA and TS-1. High yields were achieved over the CuBTC catalyst in the Knoevenagel condensation involving malonitrile, especially at a relatively low reaction temperature (80 degrees C); no leaching of the active phase was evidenced. In contrast, zeolites were not active under such reaction conditions. We propose an activation of malonitrile on a pair of adjacent Cu ions to explain the high catalytic activity of CuBTC with respect to conventional catalysts. Compared with CuBTC, zeolites exhibited usually lower selectivities, which is ascribed to a high acid strength of their active sites promoting consecutive reactions.