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.