Experiment (4) Extraction PDF

Experiment (4) Extraction Purpose: Extraction is one of the important methods for separating and purifying organic substances. Theory: - Extraction is one of the important methods for separating and purifying organic substa...

Experiment (4) Extraction Purpose: Extraction is one of the important methods for separating and purifying organic substances. Theory: - Extraction is one of the important methods for separating and purifying organic substances. It is used on a large scale in extraction organic compounds from their sources, which are known as natural products (seeds and leafs of plants). - It depends on the difference of the organic substance solubility in two different immiscible solutions, like water and chloroform. - To clarification, we assume that we have substance (x) dissolved in solvent (a). for the purpose of extraction, we are looking for another solvent (b) that has the ability to dissolve substance (x) and at the same time does not mix with solvent (a). - The solute is distributed between two unmixed liquid layers according to the distributive law. the upper layer is for the liquid of the lower density and the lower layer for the liquid of the higher density. - The extraction process takes place more than once to ensure that all substance (x) withdrawn from solvent (a), and this is known as multiple extraction. - The ratio of the concentrations of solute in the two solvents is known as the distribution or partition coefficient KD. CA KD = CB - An extracting solvent should be immiscible, have a favorable KD, doesn't react with the other solvents, have a low boiling point and be easily separated from solute. - The method is used sometimes to remove an water is usually one of the solvents used in this process, and the other solvent is an non-polar organic liquid, or slightly polar. Ether is one of the important organic solvents used extensively as an extracting solvent. It is slightly soluble in water and its efficiency in use can be improved considerably by the addition of a small amount of an ionizable salt like NaCl or K2CO3, to the water layer. This leads to an increase in the polar property of this solution that results in a decrease in the solubility of the non-polar compound.  - Among the low-boiling organic solvents used in this experiment are pentane, hexane, tetra chloromethane, chloroform, benzene, and toluene. Procedure: 1- Take 0.05g of iodine and 1.5g of potassium iodide, mix the materials together in a beaker and add 50ml water 2- put the mixture in a separatory funnel, and add 7.5ml of chloroform. 3- close the funnel hole with a stopper, shake the mixture well for 10 minutes with open the valve during shaking. 4- open the stopper for a while in order to release the excess pressure and put the funnel on a metal ring for about 10 minutes for complete separation of the two layers. 5- Note the dissolution of iodine in the organic layer through the color change of the organic layer. 6- Separate the lower layer (chloroform) slowly until the aqueous layer is about to enter the hole of the stopcock. 7- The extraction can be done either in one batch or in several batches using different volumes of the organic solvent chloroform and then calculating the E% extraction by titrating the aqueous layer in each case using sodium thiosulfate. Fig. (1): Two extractions when the organic layer is on the bottom. Fig. (2): Progress of the extraction of methyl red (the colored compound) from the acidic aqueous layer (bottom) into the organic layer (top). Fig. (3): Two extractions when the organic layer is on the top.