| The Knoevenagel condensation reaction is one of the most important condensation reactions that can be used in different areas such as cosmetics, perfumes, pharmaceuticals, calcium antagonists and polymers [1]. Usually, it is carried out in organic solvents. Bases such as ammonia, primary or secondary amines, and their salts can catalyze a Knoevenagel reaction [2--3]. Several heterogeneous catalysts such as aluminum oxide [4], alkali-containing MCM-41 [5], and zeolites [6] can also be used to catalyze this reaction. Recently, with the development of the green chemistry concept, which seeks to reduce negative environmental impact [8], the Knoevenagel condensation reaction was rewritten under greener conditions. It was found that deep eutectic solvents (DES), a mixture of two or three cheap and safe solid components that are capable of associating with each other through hydrogen bond interactions [19], are a good option to catalyze this type of reaction. DES is inexpensive, safe, and easy to recycle. This type of reaction conditions gave a high yield under a smooth process in a short time [28]. By using a deep eutectic solvent (choline chloride/urea) as a catalyst and solvent, different factors that could affect the Knoevenagel condensation reaction, such as the effect of substituted groups in active methylene compounds on the yield of the products, can be studied.;1. Tietze, L. F.; Rackelmann, N. Domino Reactions in the Synthesis of Heterocyclic Natural Products and Analogs. Pure and Applied Chemistry 2004, 76, 1967--1983.;2. Jones, G. 2011. The Knoevenagel Condensation. Organic Reactions 2011, 15, 204--599.;3. Tietze, L. F. Domino Reactions in Organic Synthesis. Chem. Rev. 1996, 96, 115--136.;4. Texier-Boullet, F.; Foucaud, A. Knoevenagel Condensation Catalysed by Aluminium Oxide. Tetrahedron Lett. 1982, 23, 4927--4928.;5. Rao, Y.; Subba, V.; De Vos, D.E.; Jacobs, P. A. 1,5,7-Triazabicyclo[4.4.0]dec-5-ene Immobilized in MCM-41: A Strongly Basic Porous Catalyst. Angew. Chem. Int. Ed. Engl. 1997, 36, 2661--2663.;6. Reddy, T. I.; Varma, R. S.. Rare-earth (RE) Exchanged NaY Zeolite Promoted Knoevenagel Condensation. Tetrahedron Letters 1997, 38, 1721--1724.;8. Anastas, P. T.; Warner, J. C. Green Chemistry: Theory and Practice, Oxford University Press: New York, 1998, p.30.;19. Abbott, A. P.; Capper, G.; Davies, D. L.; Rasheed, R. K.; Tambyrajah, V. Novel Solvent Properties of Choline Chloride/Urea Mixtures. Chem. Commun., 2003, 1, 70--71.;28. Liu, S.; Ni,Y.; Wei, W.; Qiu, F.; Xu, S.; Ying, A. Choline Chloride and Urea Based Eutectic Solvents: Effective Catalytic Systems for the Knoevenagel Condensation Reactions of Substituted Acetonitriles. J. Chem. Res. 2014, 38, 186--188. |
