Special designed menthol-based deep eutectic liquid for the removal of herbicide 2,4-dichlorophenoxyacetic acid through reactive liquid–liquid extraction

Abstract

Reactive liquid–liquid extraction (RLLE) was applied for the removal of 2,4-dichlorophenoxyacetic acid (2,4-D) from its aqueous solution. Deep eutectic liquids (DELs) was used as extractant in a conventional solvent (diethyl succinate-DES) through RLLE. Various menthol-based DELs were prepared. Menthol was used as hydrogen bond acceptor, whilst formic acid and acetic acid were hydrogen bond donor for the DEL preparations. The best 2,4-D removal was achieved by menthol/formic acid (1/2, molar ratio) combination. The menthol-based DEL increased the extraction performance of DES by almost 2–3 times. More than 90% of 2,4-D were extracted by the recommended method with the designed solvent. Thermodynamics study has been also executed. Thermodynamics of the 2,4-D transfer from aqueous phase to hydrophobic phase has been found to be spontenous and endothermic process, which is incentived by entropy. Moreover, Fourier transformed infrared-attenuated total reflectance was used for the characterization reasons of the prepared DELs. Additionally, physical properties such as pH, density, viscosity and refractive index of the products were also measured. The last but not the least, viscosity and acidity of the extraction medium were found to be effective parameters.