Dissolution for Recrystallization by Adding Small Amounts of Water to Increase Solubility in a Water-Miscible Organic Solvent
It is well known that small amounts of water have a marked influence on the solubility of many solutes when mixed into less polar organic liquids. An example is the difference in dissolving power between well dried acetonitrile and acetonitrile that has picked up just the moisture it gets standing near a steam bath for a few minutes. Years ago, Dr. Renuka Misra, an extraordinary natural products chemist then working at the University of Toronto, demonstrated this to me when I was having trouble doing a particular recrystallization.
Removing Water from a Solvent Mixture with a Miscible Polar Solvent to Causing Crystallization by Distilling an Azeotropic Composition
Another way to access the solubilizing power of water is with water azeotropes. Co-solvents that form azeotropic mixtures with water can be used to recrystallize polar materials by first dissolving them in the co-solvent assisted with some water and then distilling the azeotropic composition to remove the water as its azeotrope leaving the solute in the less polar, pure organic solvent from which it can crystallize or precipitate, often in excellent yield.
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