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Coumarin syntheses via Pechmann condensation in Lewis acidic chloroaluminate ionic liquid

Mahesh K. Potdar, Swapnil S. Mohile and Manikrao M. Salunkhe*

*Department of Chemistry, The Institute of Science, 15 Madam Cama Road, Mumbai 400 032, India, Email: mmsalunkhehotmail.com

M. K. Potdar, S. S. Mohile, M. M. Salunkhe, Tetrahedron Lett., 2001, 42, 9285-9287.

DOI: 10.1016/S0040-4039(01)02041-X


Abstract

The ionic liquid 1-butyl-3-methylimidazolium chloroaluminate ([bmim]Cl•2AlCl3) plays the dual role of solvent and Lewis acid catalyst in the Pechmann condensation of phenols with ethyl acetoacetate leading to coumarin derivatives. The reaction time is reduced drastically even at ambient conditions.

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Details

The document discusses the synthesis of coumarin derivatives via Pechmann condensation using a Lewis acidic chloroaluminate ionic liquid, specifically 1-butyl-3-methylimidazolium chloroaluminate ([bmim]Cl·2AlCl3). This method serves as an environmentally friendly alternative to conventional acid catalysts, significantly reducing reaction time even at ambient conditions. The ionic liquid acts both as a solvent and a Lewis acid catalyst, providing an efficient route to coumarin synthesis. Coumarins are valuable in various applications, including anticoagulants, food and cosmetic additives, insecticides, optical brighteners, and dyes. Traditional methods for synthesizing coumarins, such as the Pechmann reaction, often require excess amounts of acid catalysts, leading to environmental pollution. The use of chloroaluminate ionic liquids addresses these issues by minimizing waste and avoiding volatile organic compound emissions. The study found that the acidic ionic liquid with an AlCl3 mole fraction of 0.67 yielded the best results. The method was effective for various phenols, with electron-donating groups enhancing reactivity. The research highlights the potential of ionic liquids as green solvents in organic synthesis, with ongoing investigations into other condensation reactions.


Key Words

Pechmann Condensation, Ionic Liquids


ID: J72-Y2001-500