Extraction of organic compounds

Introduction :

The process of removing a substance from its aqueous solution by shaking with a suitable organic solvent is termed as Extraction. If the organic compounds are removed from aqueous solution, this process is called as Extraction of organic compounds.

Extraction of Organic Compounds with a Solvent

When an organic substance is present as solution in water, it can be recovered from the solution by the following steps:

1. The aqueous solution is shaken with an immiscible organic solvent in which solute is more soluble
2. The solvent layer is separated by means of a separating funnel.
3. The organic substance is then recovered from it by distilling off the solvent.

Procedure: The aqueous solution is placed in a separating funnel. A small quantity of the organic solvent, say ether or chloroform, is then added to it. The organic solvent being immiscible with water will form a separate layer. The mouth of the funnel is closed with a stopper or palm of the hand and shaken gently. The solute being more soluble in the organic solvent transferred to it. The solvent layer is then separated by opening the tap and running out the lower layer. The organic substance dissolved in it is finally recovered by distilling off the solvent. It is always better to extract 2 or 3 times with smaller quantities of the solvent than once with the bulk of the solvent provided.

Extraction of Organic Compounds with Soxhlet

When an organic substance is to be recovered from a solid, it is extracted by means of an organic solvent in which the impurities are insoluble. In actual practice the extraction from solids is often tedious and requires thorough contact and heating with the solvent. This is done on special apparatus. The soxhlet extractor.
Procedure: the powdered material is placed into the thimble made of stout filter paper. The flask containing a suitable solvent is heated on a water bath or sand bath. As the solvent boils, its vapors rise through the side tube up into the water condenser. The condensed liquid drop on the solid in the thimble dissolves the organic substances and filters out. As the level of liquid rises, the solution flows back into the boiling flask. The solvent is once again vaporized, leaving behind the extracted substance in the flask. In this way a continuous stream of pure solvent drops on the solid material, extracts the soluble substances and returns to the flask. At the end of the operation the solvent in the boiling flask is distilled off, leaving the organic substance behind.