Page 108 - phytochemistry general program

Separation and isolation techniques have been tremendously developed in the last .1
few decades. In the field of phytochemistry and natural products chemistry,
efficient separation methods are key steps either for the search for new drugs or

for the preparation and analysis of already present drugs.

Several methods have been used for the separation of mixtures of components.
The following methods except chromatography have been used but are of limited

uses.

Sublimation

It is the transition of a substance directly from the solid to the gas phase without
passing through the intermediate liquid phase. Sublimation is sometimes used to
isolate compounds from the whole drug. Caffeine can be isolated from tea by
sublimation. Sublimation can be also used for the purification of materials present

in crude extracts.

Distillation .2

Distillation is a process of separating the component substances from a liquid
mixture by selective evaporation and condensation. Fractional distillation has been
used for the separation of the components of volatile mixtures such as volatile oils.
On a laboratory scale, it is not easy by this method to separate minor components
of a mixture in a pure state. Steam distillation is much used to isolate volatile oils

and hydrocyanic acid from plant materials.

Fractional liberation .3

Some groups of compounds lend themselves to fractional liberation from mixtures.
As an example, a mixture of alkaloid salts in aqueous solution, when treated with
aliquots of alkali, will give first the weakest base in the free state followed by base
liberation in an ascending order of basicity. If the mixture is shaken with an organic

solvent after each addition, then fractionated series of bases will be obtained.

Fractional crystallization .4

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