Recrystallization

Recrystallization purifies a solid compound by exploiting the temperature-dependent difference in solubility between the desired compound and its impurities...

Recrystallization purifies a solid compound by exploiting the temperature-dependent difference in solubility between the desired compound and its impurities within a carefully selected solvent or solvent pair: the crude solid is dissolved in a minimum volume of hot solvent in which it is highly soluble, and slow cooling induces selective crystallisation of the purified compound while impurities, present at lower concentration, remain dissolved in the mother liquor. Solvent selection for recrystallization requires a solvent in which the target compound is poorly soluble at low temperature but highly soluble at elevated temperature, with impurities remaining soluble across the full temperature range; recrystallization remains the preferred final purification and polymorph-control step for solid pharmaceutical intermediates and active ingredients precisely because it can achieve very high purity while simultaneously controlling the crystalline form of the isolated solid, a property of direct relevance to the compound's stability and dissolution behaviour.