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Knoevenagel condensation reaction catalysed by Al-MOFs with CAU-1 and CAU-10-type structures

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Abstract

The metal–organic frameworks (MOFs) CAU-1-NH2 ([Al4(OH)2(OCH3)4(p-BDC-NH2)3], (p-BDC-NH2)2− = 2-aminoterephthalate) and CAU-10-NH2 ([Al(OH)(m-BDC-NH2)], (m-BDC-NH2)2− = 5-aminoisophthalate) which possess two different pore sizes were studied for their catalytic activity as heterogeneous solid base catalysts in the Knoevenagel condensation reaction between benzaldehyde and malononitrile under mild reaction conditions (40 °C, 7 h, ethanol). For comparison, isoreticular MOFs containing a smaller amount of –NH2 groups (CAU-1-NH2/H) or no –NH2 groups (CAU-10-H) were synthesized. A two-step synthesis route including the synthesis of CAU-1-NH2 and its use as crystal seeds was developed to obtain the mixed-linker CAU-1-NH2/H compound. Only for CAU-1-NH2, up to 100% selectivity towards the desired Knoevenagel condensation product is observed. Hence, the catalytic activity of CAU-1-NH2 was tested between various benzaldehydes containing different substituents with malononitrile. By employing benzaldehyde and malononitrile as the starting materials, it is found that the mixed-linker MOF CAU-1-NH2/H catalyses the formation of the acetal (benzaldehyde diethyl acetal), while both CAU-10 materials lead to mixtures of the two products. Furthermore, the catalyst stability was also examined through reusability and leaching experiments and it is observed that the catalyst can be reused with no significant drop in its activity.

Graphical abstract: Knoevenagel condensation reaction catalysed by Al-MOFs with CAU-1 and CAU-10-type structures

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Publication details

The article was received on 02 Jan 2017, accepted on 25 Jan 2017, published on 02 Feb 2017 and first published online on 02 Feb 2017


Article type: Paper
DOI: 10.1039/C6CE02664H
Citation: CrystEngComm, 2017, Advance Article
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    Knoevenagel condensation reaction catalysed by Al-MOFs with CAU-1 and CAU-10-type structures

    A. Dhakshinamoorthy, N. Heidenreich, D. Lenzen and N. Stock, CrystEngComm, 2017, Advance Article , DOI: 10.1039/C6CE02664H

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