Novel hydrophobic acetanilide-based deep eutectic solvents. Preparation, properties, their applications in liquid–liquid extraction

Novel hydrophobic deep eutectic solvents (DESs) based on tetrabutylammonium bromide (TBAB) as a hydrogen bond acceptor and acetanilide (ACN) as a hydrogen bond donor were prepared at different TBAB:ACN molar ratios. In order to screening of molar ratios of the DES formation, TBAB and acetanilide with 1:0.12, 1:0.25, 1:0.35, 1:0.5, 1:0.75, 1:1, 1:1.25, 1:1.33, 1:1.5, 1:2, 1:2.5, 1:3, 1:4, 1:5 and 1:8 molar ratios were investigated and their stability and thermal behaviors were studied. It was found that among all the investigated mixtures five molar ratios 1:1, 1:1.25, 1:1.33, 1:1.5 and 1:2 gave stable liquids at room temperature and the DESs with molar ratios 1:1, 1:1.33 and 1:2 were selected and their physicochemical properties, thermal behaviors and applications in liquid–liquid extractions were investigated. Thermal behavior of the prepared DESs was investigated by the DSC method. The Wilson, NRTL and regular solution activity coefficient models were used for the correlation of the solid–liquid equilibria phase diagram data of the investigated systems. In order to study the chemical structure and occurrence the hydrogen bond formation between the DES constituents, the FT-IR, 1H NMR and 1C NMR analysis were carried out. The physical properties including melting point, density, speed of sound, refractive index and electrical conductivity of the prepared DESs were investigated at different temperatures. Although TBAB is soluble and acetanilide is slightly soluble in water, the prepared TBAB:ACN DESs are hydrophobic and insoluble in water, indicate the high stability in aqueous samples and they can be used for liquid–liquid extraction in aqueous samples. The prepared DESs were successfully used for efficient extraction of congo red and methyl orange from aqueous solutions. The effects of amount of DES, concentration and type of dye, sample/solvent weight ratio and HBA/HBD molar ratio on the extraction efficiency were investigated.