A commonly used method of separating a mixture of organic compounds is known as liquid-liquid extraction. Most reactions of organic compounds require extraction at some stage of product purification. In this experiment you will use extraction techniques to separate a mixture of an organic acid, a base, and a neutral compound. Organic acids and bases can be separated from each other and from neutral compounds by extraction using aqueous solutions of different pH values. Most organic carboxylic acids are insoluble or slightly soluble in water, but these compounds are highly soluble in dilute aqueous sodium hydroxide because the acid is deprotonated by the base producing the sodium carboxylate salt.The carboxylic acid can be selectively isolated by dissolving the mixture in an organic solvent that is immiscible with water, and then extracting the solution with sodium hydroxide.
The basic aqueous solution containing the carboxylate salt is acidified, causing the sodium carboxylate salt to convert back to the carboxylic acid, which is not water soluble. The acid will precipitate from the solution, as shown here.Organic bases (e.g.
, amines) that are insoluble in water can be separated by extraction with hydrochloric acid. Addition of HCl to the amine produces the corresponding ammonium salt, which is soluble in water but not in organic solvents.The amine can be recovered from the aqueous solution by treatment with a base, converting the ammonium salt back to the amine. The amine is not water-soluble and will precipitate, as shown here.
Using your understanding of these properties, separation of a mixture containing a carboxylic acid, an amine, and a neutral compound can be carried out via sequential acid and base extractions. Some of the most challenging and time consuming laboratory procedures involve separation mixtures and purifying the components. Several common separation techniques are described.These are1) Filtration 2) Crystallization 3) Distillation 4) Extraction 5) ChromatographyAll these methods depend on the physical properties of the substances in the mixture and no chemical changes occur. Filtration: separates the components of a mixture on the bases of difference in particle size. It is used most often to separate a liquid (smaller particles) from a solid (larger particles).
Crystallization: is the process of purification of compounds in which pure solid substances are obtained or isolated from impure solution. Crystals obtained can be recrystallised again thus increasing the degree of its purity. Distillation: separates components through difference in volatility the tendency of a substance to become a gas.Furthermore extraction is also based on difference in solubility. Therefore such a process can be used to separate organic substances from inorganic impurities simply by shaking on aqueous solution or suspension with suitable immiscible solvents such as benzene, dietheylether etc.
To bring the separation process to an end, the combined organic phase is dried and the solvent is evaporated.There is sometimes the addition of electrolyte such as ammonium sulphate to the aqueous phase which helps to ensure that the organic layer separates clearly and also increases the extent of extraction into the layer. All these methods depend on the physical properties of the substances in the mixture and no chemical changes occur In choosing a suitable solvent, we need to find one in which the material to be extracted is readily soluble whereas the substance from which it is being extracted is not. The same consideration is applied not withstanding the fact that it is the substance being purified or one of its contaminants, that is taken into a new phase
