Microwave Accelerated Synthesis of 2-Oxo-2H-Chromene-3-Carboxylic Acid Using WELFSA

Background: Agro-waste derived extracts such as Water Extract of Banana (WEB), Water Extract of Rice Straw Ash (WERSA), and Water Extract of Papaya Bark Ash (WEPBA) have been recently demonstrated to be green method syntheses of some important bioorganic molecules. Such a green method terminated the use of the expensive, pollution-causing, hazardous, and toxic materials during the reaction. Coumarin-3-carboxylic acid represents a class of naturally/synthetic occurring compound with a wide range of pharmacological applications. In this paper, we demonstrated a novel and easy Knoevenagel condensation product by the reaction of salicylaldehyde (1) and Meldrum’s acid (2) catalyzed by Water Extract of Lemon Fruit Shell Ash (WELFSA) as a greener method under microwave irradiation. The reaction was completed in 2-6 min giving a final product isolation by simple workup in excellent yield with column chromatography free pure form. The product was characterized by FT-IR, 1H-, 13C-NMR and mass spectrometry techniques. Methods: Agro-waste extract as a greener reagent was used for the synthesis of 2-oxo-2H-chromene- 3-carboxylic acid under microwave irradiation method. Results: Knoevenagel condensation of salicylaldehyde (1) and Meldrum’s acid (2) was conducted catalyzed by WELFSA acting as a natural base. Firstly, the catalyst was capable to extract acidic proton from Meldrum’s acid followed by nucleophilic substitution on salicylaldehyde carbonyl group. Further, the elimination of water and acetone took place and by ring closure, resulted in a target product coumarin-3-carboxylic acid. Conclusion: We have demonstrated agro-waste extract to be an alternative green catalyst for the condensation of substituted salicylaldehyde and Meldrum’s acid. The method has advantages of being solvent-free, non-polluting, non-toxic, using cheaper catalyst, simple reaction condition and environment-friendly. The final product isolated was chromatographically pure and did not require further purification. The catalyst derived is natural and inexpensive, available in a large amount of agro-waste generated in kitchens. The method is a suitable example of a green chemistry protocol.