New Menthol-Based Hydrophobic Deep Eutectic Solvents as a Tool for Lactic Acid Extraction

In recent years, deep eutectic solvents (DESs) have attracted a lot of attention as a substitute for the current toxic organic solvents and can be applied in many chemical processes such as extraction and synthesis. The development of new deep eutectic solvents for use in the isolation of valuable biologically active substances with significant benefits for health, the environment, and others is being investigated with increasing scientific interest. Deep eutectic solvents were prepared using menthol as a hydrogen bond donor and different tertiary amines as hydrogen bond acceptors by varying the ratio of the two constituents. The DESs obtained were analyzed using densitometry, viscosimetry, IR, TGA, and DSC. The potential of the DESs for extraction and re-extraction was evaluated with a water solution of lactic acid. All the DESs obtained are suitable for the extraction of lactic acid. Deep eutectic solvents based on menthol and dioctyl amine (M/DOA 2:1), trioctyl amine (M/TOA 2:1), tridodecyl amine (M/TDDA 1:2), and trihexyl amine (M/THA 2:1) show highest results.