újrakristályosodása

Recrystallization is a purification technique used to obtain pure solid compounds from an impure sample. The fundamental principle behind recrystallization is that the solubility of a solid in a solvent typically increases with temperature. An impure solid is dissolved in a minimal amount of a hot solvent in which the desired compound is soluble, but impurities are either insoluble or highly soluble. As the solution cools, the solubility of the desired compound decreases, causing it to crystallize out of the solution in a purer form. Impurities that are more soluble remain in the solution, while those that are insoluble can be removed by hot filtration.

The choice of solvent is critical for successful recrystallization. An ideal solvent should dissolve the desired compound well when hot but poorly when cold. It should also not react with the compound being purified. Common solvents include water, ethanol, methanol, acetone, and ethyl acetate, or mixtures of solvents. After dissolving the impure solid in the hot solvent, the solution is allowed to cool slowly. Slow cooling promotes the formation of larger, purer crystals. Rapid cooling can trap impurities within the crystal lattice. Once crystallization is complete, the pure crystals are separated from the mother liquor (the remaining solution containing impurities) by filtration, usually using a Büchner funnel and vacuum filtration. The collected crystals are then typically washed with a small amount of cold, fresh solvent to remove any adhering mother liquor and dried.