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Organic Chemistry

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Distillation and Differential Extraction

Distillation: Distillation is the method of separation of volatile liquid from the non-volatile liquid which has a difference in boiling point. The liquid mixtures are taken in a round bottom flask and are heated. The vapour has a lower boiling point is collected in a receiver. Distillation  process  involves two steps:

  1. Vaporization
  2. Condensation

Some of the important distillation types are discussed below:

  1. Simple Distillation: It is applied for volatile liquid which boils without decomposition at atmospheric pressure and contains non-volatile impurities. This method can be used for separating liquids having sufficient difference in their boiling points.

Example: Hexane and Toluene, Benzene and aniline, ether and toluene etc.

  1. Steam Distillation: This is the process of co-distillation with water. This method is used for the purification and separation of the organic solid or liquid compounds which are not mixable with water, volatile in steam, contain non-volatile impurities, the high vapour pressure at the boiling temperature of the water. Steam distillation is analogous to vacuum distillation.

Example: Mixture of ortho and para isomers

  1. Fractional Distillation: Compounds whose boiling point has no significant difference in boiling point are purified through this technique. The vapour of such liquid is formed within the same temperature range and are condensed simultaneously. The liquid forming azeotropic mixture cannot be separated by this method. It is used mainly for the distillation of petroleum, coal tar, and crude alcohol. 

Example: Water and alcohol, Benzene and toluene

  1. Differential Extraction: The organic compound present in an aqueous medium is separated by shaking it with an organic compound which is more soluble than in water is called differential extraction. They are shaken until two layers of two compounds are formed and is separated by separator funnel.

 

Example: Benzoic acid can be extracted from water solution using benzene.

 

  1. Chromatography: Chromatography is the technique of testing the purity of compounds. There are two phases in this technique: Stationary phase and mobile phase. The mixture of compounds is made stationary phase while the moving phase is called the mobile phase.
  • Adsorption Chromatography: When a mobile phase is allowed to move over a stationary phase ) adsorbent) the components of the mixture are moved by the varying distance over the stationary phase.
  • Column Chromatography: Separation of the mixture over a column of adsorbent
  • Thin layer Chromatography: A thin layer of adsorbent is spread over a glass plate of suitable size, and the mixture is applied as a spot about 2 cm above one end of the TLC plate

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