Preparation and Characterization of a Heterogeneous Catalyst from Water Hyacinth (Eichhornia crassipes): Catalytic Application in the Synthesis of bis(indolyl)methanes and bis(pyrrolyl) methanes Under Solvent Free Condition

Background: Heterogeneous catalysts are the leading areas of research interest mainly due to the facilities of recovery and reusability. Water hyacinth (Eichhornia crassipes) is a renewable aquatic plant and is considered a hazard for other useful aquatic crops. In the search of a sustainable and eco-friendly process, a novel heterogeneous catalyst has been prepared from this plant for the use in the synthesis of bis(indolyl)methanes and bis(pyrrolyl)methanes. These compounds are important building blocks for the preparation of pharmaceutically significant porphyrins and related compounds such as dipyrrins, calixpyrroles, chlorins, corroles, etc. Methods: Water hyacinth, which is available in plenty in Northeast of India at no cost, is used to prepare the heterogeneous catalyst. The catalyst has been fully characterized by AAS, FESEM, BET, TGA analysis, FT IR spectroscopy, XRF, powder XRD, EDX and TEM. The efficacy of the catalyst in the synthesis of bis(indolyl)methane and bis(pyrrolyl)methanes under microwave irradiation in solvent free condition has been examined. Results: The catalyst has good thermal stability and exhibits high catalytic activity. It consists of a mixture of carbonates, oxides and chlorides of varieties of elements such as C, Si, Mg, P, S, K, Ca, Na, etc. The catalyst has proved highly effective in as many as 20 sets of reactions leading to the formation of bis(indolyl)methanes and bis(pyrrolyl)methanes. The catalyst can be reused. Conclusion: The study provides a novel application of water hyacinth (Eichhornia crassipes) which is hitherto considered an aquatic hazard for other crops. It brings into light a novel heterogeneous solid base catalyst which is cost effective, environmentally safe and recyclable, and can be used in catalytic amount in solvent free organic transformations.