Water-Organic Solvent Mixtures for Crystallization or Recrystallization

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. 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.
For example suppose you want to recrystallize a compound that dissolves in acetonitrile so long as some water is added. Acetonitrile/water have an azeotrope with bp. 70.6 C; five degrees less than acetonitrile itself. Slowly distilling this water/acetonitrile solution will remove this azeotrope leading the pot solution itself towards pure acetonitrile. The compound will start to crystallize at some point in the distillation.