Terpene-based hydrophobic (D)ESs: A systematic review of physiochemical properties

A new class of green solvents, called (deep) eutectic solvents has expanded substantially since Abbott's 2003 study. This expansion has culminated in a subclass known as hydrophobic (deep) eutectic solvents, which has sparked extensive research into their application in industry, particularly extraction technologies. Although a solvent's characteristics play a major role in its adoption in industry, it is now well known that the components used to prepare these kinds of solvents affect their properties. Furthermore, the components used can precisely adjust (or fine-tune) their characteristics for various industrial applications, including the extraction of various substances. Despite the growing number of papers on the application of (deep) eutectic solvents, including review articles, a comprehensive summary of their physicochemical features in relation to their chemical composition is either lacking or inconsistently documented. In this study review, we have collected and presented literature data on the physiochemical properties of hydrophobic terpene-based, particularly menthol-based and thymol-based (deep) eutectic solvents. Moreover, the literature data is presented in tables, and all identified inconsistencies in the properties are discussed and highlighted.