14. Hot Filtration & Recrystallization

General Remarks

The movie explains hot filtration and recrystallization of 4-methoxy-2-nitroacetanilide yielded in the following reaction which is carried out in "Organic Chemistry Experiment".

These are purification methods for crystalline compounds containing a small amount of impurities.
Insoluble impurities are removed by a filter paper by hot filtration.
Soluble impurities in the solution after the filtration are removed by recrystallization.
Even if the solubility of impurities is comparable with that of the sample, the impurities are not incorporated in the crystals but left dissolved in the solution when the crystals grow slowly
Do not shake or quickly cool the sample solution. Otherwise, small crystals with low purity forms.

Add a specified amount of distilled water to the sample. The sample should not be completely dissolved at this time.
Gently heat the mixture on an electric heater.
Heat distilled water in another beaker on the electric heater, too.
Stir the mixture and add a minimum amount of the heated distilled water to completely dissolve the sample.

Prepare the apparatuses for vacuum filtration.
Add the heated distilled water a few times through the Buchner funnel with the filter paper into the receiving beaker in the filtration chamber. Discard the heated water in the beaker.
Filtrate the heated sample solution expeditiously before the apparatuses cool down.