Sublimation - Purification of Organic compounds

Sublimation

Certain solid substances like Naphthalene or camphor when heated pass directly from solid to the vapour state without melting. The vapours when cooled give back the solid substance. This process is known as sublimation.

1.       Cotton        2.       Inverted funnel

3.       Perforated   4.       Mixture

asbestos sheet      5.       Sublimate

This process is very helpful in separating a volatile solid from a non-volatile solid. The powdered substance is taken in a China dish and covered with a perforated filter paper and an inverted funnel. The dish is carefully heated on a sand bath.

The vapours passing through the holes in the paper condense on the inner sides of the funnel. The non-volatile impurities remain in the dish.

Need for purification of organic compounds

The organic compounds obtained from natural sources are not pure. They contain a number of other compounds which occur with them. Similarly, the organic compounds prepared in the laboratory are also not pure. They are found to contain other products formed during the reaction. In order to investigate the structure and properties of an organic compound, it should be in the purest form. Hence purification of organic compounds become essential.

Various methods used for purification and separation of organic compounds are:

i)      Crystallisation

ii)   Fractional Crystallisation 

iii) Sublimation

iv) Distillation 

v)   Extraction with solvents

vi) Chromatography