Organic Chemistry – Some Basic Principles and Techniques - Methods of Purification of Organic Compounds

Sublimation: This method is used to separate sublimable compounds from non-sublimable impurities. It involves the direct transition of a solid to a vapor state on heating. Common examples include $Camphor$, $Naphthalene$, and $Anthracene$.

Crystallization: This is based on the difference in the solubilities of the organic compound and its impurities in a suitable solvent. The impure compound is dissolved in a solvent in which it is sparingly soluble at room temperature but appreciably soluble at higher temperatures.

Simple Distillation: Used to separate liquids which have sufficiently different boiling points (difference > $30K$ to $50K$) and which do not decompose on boiling. For example, a mixture of $Chloroform$ (b.p. $334 K$) and $Aniline$ (b.p. $457 K$).

Fractional Distillation: If the boiling points of two liquids are close to each other, a fractionating column is used. Vapors of the liquid with the lower boiling point pass through the column first. Examples include separation of different fractions of $Crude Oil$.

Distillation under Reduced Pressure (Vacuum Distillation): This method is used for liquids that have high boiling points or those which decompose at or below their boiling points. By reducing the external pressure, the liquid boils at a lower temperature. For example, $Glycerol$ is purified this way.

Steam Distillation: Used to separate substances which are steam volatile and immiscible with water. The liquid boils when the sum of vapor pressures of water ($p_1$) and the organic liquid ($p_2$) equals atmospheric pressure ($P$). Example: $Aniline$ is separated from an $Aniline-Water$ mixture.

Differential Extraction: When an organic compound is present in an aqueous medium, it is separated by shaking it with an organic solvent in which it is more soluble than in water. The organic solvent should be immiscible with water.

Chromatography: A technique used to separate components of a mixture based on their differential movement through a stationary phase under the influence of a mobile phase. Types include Adsorption Chromatography ($TLC$, Column Chromatography) and Partition Chromatography (Paper Chromatography).