Green Synthesis of Chalcones via Claisen–Schmidt Condensation Using a Standardised Hydroethanolic Acacia concinna Extract/ K₂CO₃ Catalytic System

Author

Kiran D. Gajhans, Kaluram N. Vidhate, Achut S. Munde, Rahul A. Waghmare


Abstract

 Chalcones (1,3-diaryl-2-propen-1-ones) are open-chain flavonoid precursors whose conjugated α,β-unsaturated ketone (enone) system underlies a wide range of reported bioactivities, including anticancer, antimalarial, anti-inflammatory, antimicrobial and neuroprotective effects. The standard laboratory route to chalcones is the Claisen–Schmidt condensation, a base- or acid-catalysed crossed aldol condensation between an aromatic aldehyde and an aryl methyl ketone followed by dehydration, conventionally carried out with strong bases (NaOH/KOH) in organic solvents. This study reports a standardised, bio-derived alternative in which a hydroethanolic extract of Acacia concinna (Shikakai), a saponin- and phenolic-rich botanical, is combined with the mild inorganic base K₂CO₃ as an aqueous-medium catalytic system for the Claisen–Schmidt synthesis of substituted chalcones 14(a–o) from acetophenones 13 and aromatic aldehydes 1(a–o), extending. A complete optimisation study was carried out, encompassing catalyst/extract loading, base loading, solvent, temperature, reaction time and catalyst reusability, together with a substrate-scope study across fifteen chalcone derivatives 14(a–o), a green-chemistry metrics framework (E-factor, atom economy and process mass intensity) for benchmarking against conventional and other reported green routes, and a full characterisation protocol comprising melting point, FTIR and ¹H/¹³C NMR spectroscopy and HRMS. The Shikakai/K₂CO₃ system provided a milder, aqueous and more sustainable alternative to conventional strong-base, organic-solvent protocols for chalcone synthesis, affording the fifteen chalcone derivatives 14(a–o) in 82–95% isolated yield under the optimised conditions (15 ml standardised extract, 15 mol% K₂CO₃, hydroethanolic medium, 60 °C, 60 min).



Keywords

Chalcones; Claisen–Schmidt condensation; Standardised hydroethanolic Acacia concinna extract; Potassium carbonate; Bio-inspired catalysis; Green chemistry metrics



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References


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