The synthesis of coumarin derivatives using choline chloride/zinc chloride as a deep eutectic solvent

In this work, choline chloride/zinc chloride was employed as a deep eutectic solvent (DES) in the green synthesis of coumarin derivatives using Knoevenagel condensation. Coumarins are important organic structures with useful application in various fields. The procedure consisted of the reaction between salicylaldehyde derivatives and active methylene compounds (dimethyl malonate, ethyl cyano acetate and ethyl 3-oxo-3-phenylpropanoate) to produce various coumarin derivatives. The general procedure is easy because of simple preparation and isolation of desired products. Moreover, the method is environmental friendly because of avoiding use of toxic solvents or hazardous catalysts. In the presented method, only 10 % of choline chloride/zinc chloride was employed as a non-toxic and biologically degradable media. All reactions have been completed under mild conditions with high yields (61-96 %). The employed DES plays both roles of solvent and catalyst in this reaction. Moreover, it has been reused four times in this procedure without important decreasing in the yield of reaction.