Novel crowned cobalt (II) complex containing an ionic liquid: A green and efficient catalyst for the one-pot synthesis of chromene and xanthene derivatives starting from benzylic alcohols

Abstract

In this work, a new Schiff base attached to an ionic liquid and a crown ether and coordinated to cobalt (II) was synthesized and then characterized by Fourier transform IR, inductively coupled plasma, X-ray diffraction, and thermogravimetric analyses. This catalyst was used in the synthesis of xanthenes and chromenes. In these syntheses, an alcohol was used instead of an aldehyde or a ketone. In all the reactions, the catalyst containing the crown ether and the ionic liquid exhibited greater activity than the analogs without them. The presence of the crown ether ring and the ionic liquid increases the solubility of the catalyst in the aqueous phase and increases its contact surface as a Lewis acid with the reactive species, increasing the alcohol oxidation process and, as a result, the speed of the reaction. Another advantage of this method is the reuse of the catalyst for up to at least six runs, the short reaction time, the use of environmentally friendly green solvents, and the good to excellent yields of products.