Microwave-accelerated Eco-friendly Performance of the Knoevenagel
Condensation Reaction with Various Active Methylene Derivat-ives
evaluation of Electrochemical Properties
Authors: Badiger Krishnappa B. , Kamanna Kantharaju 
Published: March 2023

Background:
The present work describes sustainable Knoevenagel condensation reac-tion of aryl/ heterocyclic aldehyde with various active methylene derivatives such as malono-nitrile, dimedone, ethyl cyanoacetate, ethyl acetoacetate, barbituric acid, and thiobarbituric acid is reported. The protocol was developed using water extract of mango peel ash (WEMPA), an agro-waste that emerged as a greener solvent media and in combination with microwave irradiation gave high-yield product isolation. The method noticed added advantages for the reaction faster reaction rate, inexpensive extract media, simple work-up, and not required chromatographic puri-fication. The present method synthesized various Knoevenagel condensation derivatives benzyli-dinemalononitrile, ethyl benzylidenecyanoacetate, ethyl benzylideneacetoacetate, benzalbarbituric acid, benzylidene-2-thiobarbituric acid, and 5,5-dimethylcyclohexane-1,3-diones were character-ized by FT-IR, 1H- & 13C-NMR, and mass spectrometry. Further, selected derivatives were inves-tigated for their electrochemical studies using cyclic voltammetry, and showed comparable oxida-tion and reduction potential properties.

Objective:
The objective of this work is to develop a green methodology synthesis of various active methylene derivatives via Knoevenagel condensation to give the product of benzylidine-malononitrile, ethyl benzylidenecyanoacetate, ethyl benzylideneacetoacetate, benzalbarbituric acid, benzylidene-2-thiobarbituric acid and 5,5-dimethylcyclohexane-1,3-diones.

Methods:
We have demonstrated WEMPA as a greener homogenous agro-waste catalytic medi-um for the economic synthesis of Knoevenagel condensation products. The developed method was found robust, non-toxic and solvent-free with a simple work-up to give the target product. The selected derivatives were investigated for their electrochemical studies using the cyclic volt-ammetry method.

Results:
The agro-waste-based catalyst developed avoids the use of the external organic or inor-ganic base for the Knoevenagel condensation reaction under microwave irradiation. The de-scribed method found faster, eco-friendly, simple filtration and recrystallization excellent yield, and purity of the Knoevenagel product. Further, the selected compounds (8a-8d, 9a- 9d, 10a-10d, 11a,-11c, 12a, 12b, and 13a-13c) were subjected to electrochemical behavior studies and showed good oxidation and reduction properties.

Conclusion:
In summary, we have established an efficient, simple, inexpensive agro-waste based catalytic approach for the synthesis of benzylidinemalononitrile, ethyl benzylidenecyanoacetate, ethyl benzylideneacetoacetate, benzalbarbituric acid, benzylidene-2-thiobarbituric acid and 5,5-dimethylcyclohexane-1,3-diones derivatives under microwave irradiation described. The catalyst is agro-waste derived, which is abundant in nature and recyclable without loss of activity after the four-run of the reaction, thus making the present approach a greener one. The advantages of the approach are inexpensive, chemical base free, requiring no external metal catalyst, short reaction time, and simple work-up isolated excellent yields of the product. For the first time, herein, we reported the electrochemical behavior of the products prepared, and showed good oxidation and reduction properties, and these molecules will emerge as good antioxidant agents.

other:
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