Sublimation

Method of Separation of Organic Compound – Sublimation

Process of conversion of material from solid state to gaseous state without undergoing into liquid state is called sublimation.

This process generally used in separation of sublimable compounds from non sublimable impurities. In this process, organic compound with non sublimable impurities is heated. After some time sublimable organic compound starts vaporizing, thus, it settles down in the conical flask. Whereas, the non sublimable impurities remains at the bottom of the flask. For example, some sublimable compounds are iodine, ammonium chloride, naphthalene, camphor, etc.

Crystallization

Crystallization is very common method of purification of organic compound. Impure compound is dissolved in solvent, in which it is more soluble. Concentrate the solution by continuous heating, until the solution reaches to its saturation point. Leave solution to cool down completely. When solution is completely cooled, small crystals of substance appears in the solution. However, even after the formation of crystal some amount of solution is left, known as mother liquor. Crystals are separated. It is interesting to know that, if compound is highly soluble in one solvent and less soluble in another, then crystallization can be done by mixing both the solvents. However, impurities that impart color to solution are removed by adsorbing over an activated charcoal. Make sure that crystallization is repetitive, if compounds have comparable solubility.

Distillation

Methods of Purification of Organic Compounds – Distillation

Process of distillation is used to separate liquids having difference in boiling point. For this, take a mixture of liquids in round bottom flask and heat this mixture. Liquid with lower boiling point vaporise first. These vapors are cooled in the condenser and is collected in flask. Later, vapors of higher boiling point rises, cools and collects down in the flask. This method is also known as simple distillation. Chloroform and aniline is separated by simple distillation. Now think of the situation where there is very less difference boiling point of two liquids. In such situation fractional distillation is carried out by adding fractional column in distillation flask. In this distillation vapors of both liquid rises in fractional column, but vapors of liquid with high boiling point face obstruction, condenses and fall off in the flask. Meanwhile, vapors of low boiling point rises up, moves to condenser, cools down and gets collected in the flask. In this way both liquids get separated. Another type of distillation is steam distillation. This technique is used to separate steam volatile substances from those which do not mix with water. For example, Aniline and water are separated by this method.

Differential Extraction

Organic compounds like benzene, ether do not mix with water but mix with other organic compounds. Thus, these are helpful in extraction of organic compound from its aqueous solution, by using method of differential extraction. Take aqueous solution of organic compound in separating funnel. Now, add a solvent in which organic compound is more soluble in comparison to water. Shake the funnel vigorously, so that, organic compound mix with solvent and allow the mixture to settle, until two distinct layers appears in the funnel. These layers contain solvent with organic compound and water. Separate it using separating funnel. Collected organic compound in the solvent can be separated by the process of distillation.

Chromatography

Chromatography is technique used for separation, isolation, purification and identification of constituents of mixture. In this technique, two phases are included, stationary phase and mobile phase. Mixture to be separated is dissolved in moving phase, then it is allowed to move slowly over stationary phase. The component of mixture gradually gets separated from each other. Chromatography is of two types adsorption chromatography and partition chromatography.

• Adsorption chromatography:
  A chromatography in which different compounds are adsorbed on adsorbent at different degrees in called adsorption chromatography. Some well known adsorbent are silica gel, alumina, etc. Mobile phase is allowed to move on stationary phase. Two types of adsorption chromatography are column chromatography and thin layer chromatography.
• Partition chromatography:
  A chromatography based on continuous differential partitioning of components of mixture between stationary and mobile phase. For example, paper chromatography is type of partition chromatography. The solution of mixture is spotted at the base of the chromatography paper. This strip of paper is then placed in the solvent which acts as a mobile phase. Solvent then rises up through the strip, thereby retaining different components. Strips containing these components is called chromatogram. Spots are generated at different heights from initial spot on the chromatogram. Spots which are generated due to colorless compounds are observed in ultraviolet rays or by spraying specific reagent.
  In upcoming blogs, we will discuss in detail about chromatography.

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Keywords: Sublimation, Distillation, Fractional distillation, Steam distillation, Crystallization, Differential extraction, Chromatography, Chromatogram

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