Kamis, 02 Juni 2011

Extraction Theory and Practice

Extraction is a physical process by which a compound (solute) is transferred from one phase to another, usually from a liquid or a solid to another liquid. The solute is removed from one phase by adding to it an immiscible solvent in which the solute is more soluble. 

  • Liquid-liquid extraction  
Liquid-liquid extraction involves the distribution, or partitioning, of a solute between two immiscible liquid phases. In the organic laboratory, the most common process involves the extraction of an organic compound from one liquid phase to the other. The two liquid phases are usually, but not always, an aqueous solution and an organic solvent. A simple extraction is often used in the work-up of an organic reaction mixture (the isolation and purification of a reaction product is often called the "work-up" of the reaction mixture), but extraction can also be used to separate and purify organic compounds. Whatever extraction protocol is being  used, most extraction operations in the organic laboratory are carried out in  separatory funnels. [more
  • Choice of extraction solvent  
Although water is almost always one of the liquids in the liquid-liquid extraction process, the choice of organic solvent is quite wide. A good extraction solvent needs four essential features: (1) it has to be practically immiscible with water; (2) it has to have a different density to water; (3) it needs good stability and volatility so that it can easily be removed from the organic compound by evaporation; (4) the solute you want to extract has to dissolve easily in it.  Table 1. Some common extraction solvents [more
  • Solid-liquid extraction  
Solids can also be extracted using organic solvents. One very simple way of doing this is to place the solid in an Erlenmeyer flask, cover the solid with the organic solvent and allow the flask to stand with occasional swirling. The organic compound that you are interested in will be slowly leached out of the solid. The unwanted solid can then be removed from the organic solution containing your compound by simple filtration. This is, however, a fairly inefficient technique in terms of extracting all of the organic compound in question, although the efficiency of the extraction can be improved by using hot solvents [more 
  • Solution drying 
After completing the isolation or purification of an organic compound by some form of extraction, or after completing the work-up of your reaction mixture, you are left with an organic solution containing your required compound. Since the organic solution has been extracted or washed with aqueous solutions, it will contain some water. Although the amount of water can sometimes be reduced by washing the organic solution with saturated sodium chloride solution, the last traces of water have to be removed by treatment with a  drying agent. [more
  • Experimental procedure 
  • Picture of Laboratory equipment for extraction experimen 
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