It is quite well known that acetonitrile and any hydrocarbon liquid upon mixing together will separate into two layers. It is very much more poorly recognized that the polarity of the acetonitrile can be tweaked by the addition of either water (5-20%) or ethylene glycol (5-40%) or a more finely refined tertiary combination of these while not disturbing the separability of the two phases, which remain essentially immiscible. Furthermore, because all of the hydrocarbon solvents have lower densities than any of acetonitrile, ethylene glycol, or water, the hydrocarbon liquid phase will consistently be the top-most layer.
How can this be practically useful? Using a small amount of an appropriately designed immiscible polar liquid phase in this way, a mixture in a hydrocarbon solution can be freed from polar impurities by multiple extractions.
This could be much more efficient, not to mention simpler and faster, than crystallizing a product from a mixture that still contains such polar impurities.
The research upon which this suggestion is based is Leshchev S.M.; Rumyantsev, I. Yu. Zh. Prikl. Khim 1992, 65(6), 1332-6 identified in CA 118: 88569f.
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