Behavior of quaternary ammonium salts and terpenoids-based deep eutectic solvents in aqueous phase

Abstract

Numerous articles have been presented on efficient liquid–liquid extraction procedures from aqueous samples using deep eutectic solvents based on quaternary ammonium salts or natural terpenoids as hydrogen bond acceptors and fatty acids as hydrogen bond donors. However, precursors of these solvents are soluble in the aqueous phase and the composition of the solvents can be changed in the presence of water. In this research the stability and composition of deep eutectic solvents based on quaternary ammonium salts (tetrabutylammonium bromide and tetraoctylammonium bromide), terpenoids (menthol and thymol) and fatty acids (hexanoic, heptanoic, octanoic, nonanoic and decanoic acids) in aqueous phase were systematically investigated. It was shown that all studied two-component solvents are transformed into three-component solvents in the presence of water. Effects of hydrogen bond acceptors and donors type on formation of three-component solvents were investigated and discussed. It was established that, the ratio of aqueous and organic phases plays a key-role for stability of the solvents based on tetrabutylammonium bromide. The solvents based on terpenoids and tetraoctylammonium bromide remain stable in the wide range of phases ratios. In addition to the study of stability, changes in the physicochemical and extraction properties of ternary eutectic solvents in comparison with two-component solvents have been shown.