Agro-Waste Sourced Catalyst as an Eco-Friendly and Sustainable Approach for Knoevenagel Condensation Reaction

Background: The present work describes an eco-friendly and sustainable approach for the Knoevenagel condensation of an aromatic aldehyde with ethyl cyanoacetate, and salicylaldehyde with Meldrum acid for the synthesis of ethyl benzylidenecyanoacetate and 3-carboxy coumarin (2-oxo-2H-1-benzopyran) derivatives, respectively. The reaction was performed under green catalytic media-Water Extract of Watermelon Fruit Peel Ash (WEWFPA), which is an eco-friendly protocol derived from the agro-waste feedstock. Various protocols have been reported for the synthesis of Knoevenagel condensation reaction using a hazardous catalyst or/and solvents found toxic to the environment, requiring longer reaction time, giving poor yield, and requiring purification of the final product. The method at hand provides several added advantages like: being a completely green method, economic, inexpensive catalyst, and the final product isolated is in pure form with good yield. Objective: The objective of the study was to develop a green methodology for the synthesis of ethyl benzylidenecyanoacetate and 3-carboxy coumarin derivatives. Results: The agro-waste based catalyst developed in the present study avoids the use of external inorganic/ organic bases and additives. Knoevenagel condensation of ethyl benzylidenecyanoacetate and 3-carboxy coumarin derivatives is carried out under room temperature using microwave irradiation, which is a solvent-free synthesis, requiring less time and giving better yield. Methods: We have demonstrated that WEWFPA can be employed as a green homogenous agrowaste for the synthesis of ethyl benzylidenecyanoacetate and 3-carboxy coumarin derivatives under rt stirring and microwave irradiation in a very economical way. The developed method is found to be simple and robust, non-hazardous and solvent-free to obtain the target product. Conclusion: In conclusion, we have established an efficient, simple, agro-waste based catalytic approach for the synthesis of ethylbenzylidenecyanoacetate and 3-carboxy coumarin derivatives employing WEWFPA as an efficient catalyst under rt stirring and microwave synthesis. The method is a green, economical and eco-friendly approach for the synthesis of Knoevenagel condensation products. The advantages of the present approach are that the reaction is a solvent-free synthesis, requiring no external metal catalyst, chemical base free, short reaction time and excellent yield of product. The catalyst is agro-waste derived, which is abundant in nature, thus making the present approach a greener one.