A Facile Deep Eutectic Solvent (DES) Mediated Green Approach for the Synthesis of Fluorescein and Phenolphthalein Dyes

Abstract Owing to the giant significance of organic dyes in both analytical as well as supramolecular chemistry, here, we report an efficient and green methodology for the preparation of indicator dyes, namely fluorescein and phenolphthalein. This particular method involves an inexpensive, reusable, and biodegradable deep eutectic solvent (DES) of choline chloride (ChCl) and zinc chloride (ZnCl 2 ) in a ratio of 1 : 2, to furnish the corresponding dyes with an appropriate stoichiometry of the easily accessible starting materials. Strikingly, in this procedure, DES played a two‐fold role both as a catalyst as well as solvent and was efficiently recycled for four successive runs with no substantial cascading in the yields of the anticipated products. This simple yet efficient environmentally realistic protocol, to our best knowledge, is the first method, whereby DES has been employed in the successful preparation of any dye molecule to date. Hopefully, this novel procedure for dye(s) synthesis will be of much importance not only from the researchers perspective, but it will also provide a new way for both undergraduate and postgraduate level experiments.