Crystal Growth by Liquid Diffusion
Substances that are very soluble in one solvent and insoluble in a second solvent may be good candidates for crystal growth by vapor diffusion, two solvent evaporation or liquid diffusion. The two solvents must be miscible (soluble in each other in all proportions). For liquid diffusion, the two solvents should have different densities.
- Make and filter a saturated solution of the substance. Carefully layer the solution and the poor solvent in a long, thin tube. (NMR tubes or glass tubing with one end closed, for example.) This layering may also work in a beaker or round-bottom flask, but it is easier to observe the crystal growth in the thin tubes. The liquid with the greater density should be on the bottom and the less dense liquid added so as not to cause mixing at the interface. - Some possible "good solvent/poor solvent" pairs are: aromatics/alkanes (Toluene/hexane, for example.), aromatics/ alcohols, and THF/hexane. (Caution: tetrahydrofuran tends to disorder in crystals.)
Thanks to Dan Smith, Goshen College, for useful discussions.