Summarizing the Effect of Acidity and Water Content of Deep Eutectic Solvent-like Mixtures—A Review

Deep eutectic solvent-like (DES-like) mixtures re-emerged in green chemistry nineteen years ago and yet have led to a large number of publications covering different research areas and different application industries. DES-like mixtures are considered a special class of green solvents because of their unique properties, such as high solubilization ability, remarkable biocompatibility, low production cost, low volatility, relatively simple synthesis methods, and considerable stability. Several studies have been published that analyze the effect of acidity/alkalinity and water content in DES-like mixtures on their physicochemical properties and behavior. This work summarizes the characterization of green solvents and, subsequently, the influence of various factors on the resulting pH values of green solvent systems. Part of this work describes the influence of water content in DES-like mixtures on their physical and chemical properties. The acidity/alkalinity effect is very important for green solvent applications, and it has the main impact on chemical reactions. As the temperature increases, the pH of DES-like mixtures decreases linearly. The type of hydrogen bond donors has been shown to have an important effect on the acidity of DES-like mixtures. The water content also affects their properties (polarity, solubilization capacity of DES-like mixtures).