Synergistic Solvation Effects: Enhanced Compound Solubility Using Binary Solvent Mixtures

We explain the concept of solubility synergistic solvation (also known as parabolic solubility), wherein a binary solvent mixture exhibits a higher solubility than either of the component solvents alone. In cases where a compound has poor solubility in pure solvents, a binary solvent mixture may be used to enhance its solubility; however, the obvious challenge is how to identify such solvent pairs efficiently and economically as the number of all possible binary solvent combinations is prohibitively large. After analyzing 33 879 pieces of compound solubility data that were collected from solvent mixtures, we conclude that synergistic solvation may be more common than generally appreciated, the magnitude of which oftentimes is significant enough to make the use of binary mixtures more advantageous than pure solvents. For charged solutes, we confirmed that adding a small amount of water to organic solvents would often improve their solubility substantially. As for noncharged solutes, we identified four “privileged solvent pairs” that are strongly synergistic. In this report, four case studies are discussed which illustrate how synergistic effects have been used to support chemical process development in different ways.