Re-crystallization is a nice way of purifying a product, but choosing a suitable solvent, if you can't rely on the literature, seems like a lot of trial-and-error.

  • Are there any general rules on which kind of solvents could be used for re-crystallization?
  • Which criteria should one use when trying to recrystallize a compound for which no literature on usable conditions are available?
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    $\begingroup$ I would argue that we should say it is more of an art than just brute force, but sometimes the distinction between the two is very arbitrary. $\endgroup$ – Chris Apr 26 '12 at 17:53

Generally speaking, the best solvent will be dependent on the impurity that you are trying to remove.

The solvent must dissolve both the desired compound and the impurity at a high temperature, but only the desired compound at lower temperatures. The solubility product of the impurity, as well as the common ion effect should both be taken into consideration.

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    $\begingroup$ At the worst, one might have to resort to a mix of solvents; if you can find a pair of mutually miscible solvents where your impure solid is soluble in one and insoluble in the other, then this might be the way to go. Of course you have the risk of oiling out... $\endgroup$ – user95 Apr 26 '12 at 6:12

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