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Catalysis by an ionic liquid: efficient conjugate addition of thiols to electron deficient alkenes catalyzed by molten tetrabutylammonium bromide under solvent-free conditions

Brindaban C. Ranu*, Suvendu S. Dey and Alakananda Hajra

*Department of Organic Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Calcutta 700032, India, Email: ocbcriacs.res.in

B. C. Ranu, S. S. Dey, A. Hajra, Tetrahedron, 2003, 59, 2325-2331.

DOI: 10.1016/S0040-4020(03)00289-8


Abstract

Tetrabutylammonium bromide is an inexpensive ionic liquid, which efficiently catalyzes the conjugate addition of thiols to α,β-unsaturated nitriles, carboxylic esters, ketones and aldehydes as well as nitro olefins.

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Details

The document discusses a study on the efficient conjugate addition of thiols to electron-deficient alkenes catalyzed by molten tetrabutylammonium bromide (TBAB) under solvent-free conditions. This method is significant for carbon–carbon bond formation in organic synthesis, particularly for producing compounds with promising biological activities. The use of TBAB, an inexpensive and readily available ionic liquid, offers a green and cost-effective alternative to conventional room temperature ionic liquids, which are often expensive and potentially toxic.

The experimental procedure involves mixing the alkene and thiol with molten TBAB at 100–105°C and stirring for 1–2 hours. The reaction mixture is then extracted with ether, and the crude product is purified by column chromatography. The TBAB can be recycled without loss of efficiency. The study found that both aromatic and aliphatic thiols react with various conjugated alkenes, including a,b-unsaturated nitriles, carboxylic esters, ketones, aldehydes, and nitro olefins, yielding high-purity products.

The research highlights the advantages of using molten TBAB, such as high yields, simplicity, cost efficiency, and environmental benefits by avoiding toxic catalysts and solvents. The study concludes that this methodology has significant potential for further applications in organic synthesis.


Key Words

thiol, alkene, tetrabutylammonium bromide, conjugate addition, solvent-free reaction, ionic liquids


ID: J72-Y2003-500