Method of purification of organic compound
1.
2.
3.
4.
5.
Sublimation
Crystallization
Distillation
Solvent Extraction(differential extraction)
Chromatography
1. Sublimation
The process of conversion of solid to vapour state directly by heating without passing
through liquid state is called sublimation.
Solid ⇌ Vapour
 For purification of solids
 For separation of sublimable volatile solids from not sublimable impurities
 E.g Camphor, naphthalene, Anthracene, Benzoic Acid, Phthalic anhydride,
Anthraquinone, Indigo, Iodine, HgCl2
2. Crystallisation
 Used for purification of solid organic compounds
 Based on difference of solubilities of the compound and impurities in a suitable
solvent.
 Impure compound dissolved in a solvent is sparingly soluble at low temp. , but
appreciably soluble at high temp.
 The process of separation of different compounds of a mixture by repeated
crystallization is called fractional crystallization.
 Fractional Crystallization
1. Used for separation of two or more soluble substances that have
different solubilites in the same solvent.
2. Most common solvent for crystallization are- Water, Alcohol, Ether,
Chloroform, Carbontetrachloride, acetone, benzene, Petroleum ether,
3. Sugar have common slat impurity so can be crystallized from hot
ethanol, as sugar dissolves in it but salt does not.
4. Fractional distillation can be used to separate a mixture of KClO3(less
soluble) and KCl (more Soluble).
3. Distillation
Imp method to separate
(i)
Volatile liquids from non-volatile impurities.
(ii)
Liquids having sufficient difference in boiling points
1. Simple Distillation
Used for purification of liquids that does not undergo decomposition at their boiling
points.
 “ The vaporization of a liquid by heating and subsequent condensation of vapours
by cooling is known as distillation”
 B.P. difference > 40° C can be purified by this method
 E.g Chloroform(B.P. 334K) & Aniline(B.P. 457K) ,, Ether(B.P. 308K) & Toluene(B.P.
384K) ,, Benzene(B.P. 353K) & Aniline(B.P. 475K)
2. Fractional Distillation


Used when B.P. difference less than 40° C
Vapours of liquid mixture passed through fractionating column before
condensation, which is fitted over mouth of the round bottom flask.
Some Important Points:
1. Liquids forming const. boiling mixture(azeotropic mix.) cannot be
separated
2. Used for crude oil separation in petroleum industry
3. Used for separation of acetone(B.P. 330K) & methyl alcohol(B.P. 338K)
4. Used for separation of benzene and toluene
3. Distillation under reduced pressure(Vacuum distillation)
 Used to purify liquids having very high B.P. which decompose at or below their
boiling points.
 Liquids made to boil below their boiling point by reducing pressure
 Pressure reduced by water pump or vacuum
Some Important points
1. Glycerine purified by this
2. H2O2 , Formaldehyde purified
3. Glycerol separated fromspent-Iye in soap Industry
4. Sugar cane juice is concentrated(saves lot of fuel)
4. Steam distillation
 Used for separation & purification of organic compounds
 Steam volatile
 Insoluble in water
 Posess high pressure (10-15 mm of Hg at 373K)
 Contains non-volatile impurities
 Based on Dalton’s law of partial pressure.
 E.g. Aniline, nitrobenzene, Bromobenzene, o-nitrophenol, o-hydroxy
bezaldehyde (Salicylaldehyde), o-hydroxy acetophenone, turpentine oil,
Essential oils.
4. Solvent Extraction(differential extraction)
 Organic compounds in aqueous medium
 Extracted by shaking with an organic solvent more soluble than in water
 Solvent should be immiscible with water & organic compound to be separated
should be highly soluble in it.
 Organic solvent & aqueous sol. Are immiscible with each other- so to form two
distinct layer- to be separated by funnel
 Organic solvent is distilled or evaporated to get organic compound
 E.g. Benzoic acid by using benzene,
 Ether is better Solvent in differential extraction due to
(I) It’s less polarity
(II) Least reactivity
(III) Higher Solubility of organic Compounds
5. Chromatography – Based on adsorption phenomenon. Common Adsorbent- Alumina