Elsevier

Catalysis Communications

Volume 12, Issue 15, 15 September 2011, Pages 1496-1502
Catalysis Communications

Short Communication
A new silica based substituted piperidine derivative catalyzed expeditious room temperature synthesis of homo and hetero bis-Knoevenagel condensation products

https://doi.org/10.1016/j.catcom.2011.05.033Get rights and content

Abstract

A new silica based piperidine derivative has been designed, synthesized and characterized by solid state carbon 13 CP MAS NMR, BET surface area analysis, IR, TGA studies, elemental analysis and pH experiment. This has been efficiently utilized as a recyclable catalyst for both homo and hetero bis-Knoevenagel condensation products in aqueous-ethanol. This is the first report of the synthesis of hetero bis-Knoevenagel condensation products by our designed catalyst.

Graphical abstract

Research Highlights

► Synthesis and characterization of heterogeneous silica based piperidine catalyst. ► Utilization for the synthesis of bis-homo and bis-hetero Knoevenagel products. ► Recyclability of the solid catalyst at least upto eight cycles. ► Sequential addition of the active methylene compounds afforded bis-hetero products.

Introduction

The increasing demands of environmental legislation promote the chemical industries to minimize waste production in chemical manufacture [1]. The use of heterogeneous catalyst, in particular organosilane [2] having a covalently anchored organic spacer to create organic–inorganic hybrid catalysts, have greatly developed in different areas of organic synthesis due to their environmental compatibility combined with good yield and selectivities. In fact, the last decade has witnessed a growing interest in the building up of organic–inorganic hybrid catalysts using several types of supports and immobilization strategies [3], [4], [5], [6], [7], [8]. Our present work is directed to immobilize 1-(2-chloroethyl)piperidine onto the silica support and to apply it towards the synthesis of homo and hetero-bis-Knoevenagel condensation products. Interestingly, 1-(2-chloroethyl)piperidine chemistry may provide straightforward possibilities for catalyst design, together with a simple immobilization procedure compared to other less-functionalized organocatalysts.

In our present study, we report the formation of hetero-Knoevenagel-dicondensation as well as homo-dicondensation products. This is the first report of the synthesis of hetero-Knoevenagel-dicondensation products. Here lies the novel application of our catalyst towards such synthesis. In addition, the synthesis of homo-bis-Knoevenagel condensation products is very rare. It is mainly for this reason that we took up the idea of synthesizing bis-homo and the challenge of preparing hetero-Knoevenagel-dicondensation products. The non-formation of bis-hetero product with most of the earlier reported catalysts is due to the enhanced reactivity of active methylene compounds towards the benzene-dicarboxaldehydes. The same active methylene compound attacks at both aldehyde functionalities simultaneously thereby resulting in the formation of homo-dicondensation products. Our strategy was to decrease the reactivity of active methylene compounds, so that, after addition of one of the active methylene compounds, the mono-Knoevenagel-condensation intermediate could be isolated. Then, adding the other active methylene compound, it would be possible to prepare hetero-dicondensation product. The subsequent discussion describes the unique property of our catalyst over previously reported basic catalysts in isolating the mono-Knoevenagel-condensation intermediate.

Section snippets

Results and discussion

Scheme 1: On the basis of the high advantages of heterogeneous solid catalysts, we designed the synthesis of the following new silica based basic catalyst containing substituted piperidine as basic unit (Scheme 1).

Conclusion

In conclusion, we have shown that our designed and synthesized silica based substituted piperidine (4) prepared from commercially available and cheap starting materials, catalyzed very efficiently the formation of both the bis-homo and hetero-Knoevenagel condensation products at room temperature. The catalyst shows high thermal stability and was recovered and reused without any noticeable loss of activity. Mild reaction condition, simplicity of procedure, general applicability, high yields

Acknowledgements

One of the authors (SR) thanks the Council of Scientific and Industrial Research, New Delhi for his fellowship (JRF). We thank the CAS Instrumentation Facility, Department of Chemistry, University of Calcutta for spectral data. We also acknowledge grant received from UGC funded major project, F. no. 37-398/2009 (SR) dated 11-01-2010. Moreover, NMR Research Centre, IISc, Bangalore-560012 is gratefully acknowledged for the solid state carbon-13 CP-MAS NMR spectrum.

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