Recrystallization is a technique that use to purify solid compounds. Recrystallization is based on the principles of solubility: compounds (solutes) tend to be more soluble in hot liquids (solvents) than they are in cold liquids. If a saturated hot solution is allowed to cool, the solute is no longer soluble in the solvent and forms crystals of pure compound. Impurities are excluded from the growing crystals and the pure solid crystals can be separated from the dissolved impurities by filtration. The products from many synthetic preparations are seldom pure and the technique of recrystallization, which involves dissolving the impure material in a hot solvent and then cooling the solution to produce crystals, is routinely used to purify covalent organic and inorganic solids.

1. Submitted by,
Name: Sayyed Atik Nisar
Class: B.Pharmacy final year
Seat No: GBP800467
Project Guide:
Mr. Ansari Altamash
Assistant Professor
YBCCP, Aurangabad
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2021-2022

2. Introduction to Recrystallization
Types of impurities, which are removed by the
recrystallization process
Need Of Recrystallisation
Solvent For Recrystallization
General Procedure for Recrystallization
Common Problems Encountered in
Recrystallization.
Other Recrystallization Techniques
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3. Recrystallization is a technique that use to purify
solid compounds.
Recrystallization is based on the principles of
solubility: compounds (solutes) tend to be more
soluble in hot liquids (solvents) than they are in cold
liquids.
If a saturated hot solution is allowed to cool, the
solute is no longer soluble in the solvent and forms
crystals of pure compound. Impurities are excluded
from the growing crystals and the pure solid crystals
can be separated from the dissolved impurities by
filtration.
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4. 1. Insoluble material: anti-bumping granules,
pieces of filter paper, traces of drying agents, grit,
hair and other materials which may have been
present in the starting chemicals.
2. Small quantities of unreacted starting chemicals
and/or by-products from side reactions or other
isomers
3. Very small amounts of coloured by-products
resulting from oxidation or polymerization of the
chemicals used.
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5. Solid Compounds synthesized in the organic
laboratory usually needs to be purified before final
confirmation tests are performed
One of the most commonly used technique to purify
a sample is recrystallization followed by vaccume
filtration
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6. The Solute Particles are generally insoluble in cold solvent but
soluble in the hot solvent.
The solvent should be volatile enough to be removed by
evaporation.
The solvent Should not react with the substance to be purified.
Solubility of organic Compounds is a function of the polarities
pf both the solvent and solute; Like Dissolve Like; Polar solvent
dissolve polar solutes; non-polar solvents dissolve non-polar
solutes
Compounds with functional groups that can form hydrogen
bonds(-OH, -NH, -COOH, -CONH) will be more soluble in
hydroxyl(polar) solvents such as Methanol and water.
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7. Should dissolve all of the compound when the
solvent is hot(boiling).
Should dissolve none of the compound when the
solvent is at room temperature.
Should have al lower boiling point than the the
meliting point of the compound.
Should have different solubilities for the compound
and the impurities.
Shoud be cheap, non-toxic, non-reactive and non-
smelly.
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9. 1. Select a suitable solvent
2. Dissolve the impure solid in minimum amount of
warm solvent
3. When the impure solid has completely dissolved,
filter the heated solution. Evaporate a portion of
the solvent to bring it to the point of saturation.
4. Cool the saturated Solution to reduce solubility.
Crystallization sets in.
5. Isolate the solid by filtration, then Dry the Crystals.
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11. Crystals do not form when the solution is cooled.
 The compound forms an oil instead of a solid.
The crystals dissolve when they are rinsed with
solvent during filtration
The recovered product is not of high purity.
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12. A. Mixed Solvent
Recrystallization
Sometimes no single solvent
possesses the desired solubility
properties: soluble in hot
solvent and insoluble in cold
solvent.
In this case, a mixed solvent
system may be used.A mixed
solvent consists of two
miscible solvents, one in
which the substance is soluble,
and the other in which the
substance is insoluble.
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13. B. Removal of Colored and Solid Impurities
If the sample is contaminated with impurities that are
colored or impurities that remain solid when the
compound is dissolved in hot solvent, the two
methods below are used to separate them from the
desired compound.
1. Removal of colored impurities by addition of
Norite .
2. Removal of solid impurities from hot solvent by
hot filtration
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