Menthol-based deep eutectic solvent for the separation of carbamazepine: reactive liquid-liquid extraction

Menthol-based deep eutectic liquid has been used for the reactive liquid-liquid extraction of the carbamazepine from its aqueous solution after it was synthesized by heating and mixing. Diethyl succinate was used as diluent, while deep eutectic liquid was the extractant. Several deep eutectic liquids containing menthol and carboxylic acids (acetic acid and formic acid) with different molar ratios (1/1 and 1/2) were composed. pH, density, viscosity, and refractive index values of the designed deep eutectic liquids were measured. Furthermore, Fourier transform infrared spectroscopy method was also applied into the deep eutectic liquids for characterization. Deep eutectic liquid increased the extraction performance of the diluent from 11 to 36% comparing to the untreated one. The proposed system (menthol/acetic acid with 1/1 of molar ratio) has extracted more than 90% of the target pharmaceutical compound from its aqueous solution in 30 min. The concentration of extractant in the diluent, initial carbamazepine content in aqueous media, and ionic intensity have influenced the reactive liquid-liquid extraction. Depending on the thermodynamics outcome, the transfer process of carbamazepine from aqueous phase into hydrophobic phase is an endothermic and spontaneous in nature. It has been also observed to be a separation process with a structure that tends to be irregular.