Evaluation of sodium acetate trihydrate–urea DES as a benign reaction media for the Biginelli reaction. Unexpected synthesis of methylenebis(3-hydroxy-5,5-dimethylcyclohex-2-enones), hexahydroxanthene-1,8-diones and hexahydroacridine-1,8-diones†
In this work, the low melting mixture sodium acetate trihydrate–urea was synthesized and the eutectic composition was determined and characterized using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The physical properties of the deep eutectic solvent (DES) such as viscosity, electrical conductivity, density, pH and refractive index were measured and analyzed as a function of temperature. To explore the use of this DES as a reaction media, the Biginelli one-pot reaction for the preparation of polyhydroquinoxaline derivatives was studied and unexpectedly methylenebis(3-hydroxy-5,5-dimethylcyclohex-2-enones) and hexahydroxanthene-1,8-diones were obtained when the reaction was performed at 60 °C, and hexahydroacridine-1,8-diones when the reaction was conducted at 100 °C. Our results showed that the nature of the obtained products can be tuned by increasing the temperature of the reaction.