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Re-crystallization

Re-crystallization

Re-crystallization

Re-crystallization

It is a technique used in chemistry to purify a compound by dissolving the smaller crystals and impurities present into it in a suitable solvent. But there is one important thing to be considered is that there should be a difference in the solubility of product and impurity in the selected solvent for re-crystallization. The selection of solvent is based on the property that organic compound should be dissolved in hot solvent but not in cold. Once it gets dissolved filter it immediately with preheated funnel, now insoluble impurities are separated out but soluble impurities are still in filtrate. So now cool it down so that organic compound crystals out, this is because it is not soluble in cold solvent and now by filtration or decantation pure crystals can be separated out by soluble impurities. This is how via re-crystallization soluble and insoluble both kinds of impurities can be removed from synthesized organic compounds.

This is how purification takes place by the re-crystallization process.

Application:

  • To purify the sample or remove impurities.
  • Separation and isolation of compounds.
  • Synthesis of pure pharmaceutical drugs, co-crystals.
  • To separate chiral isomers.

Disadvantage:

  • If the solubility of impurity and solute is the same then difficult to use this technique.
  • Sometimes precipitate get dissolved in a solvent with impurity.
  • Variable temperature has variable effects
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