2ExtractionA method of separate an organic compound from a mixture of compounds.It is a process that selectively dissolves one or more of the mixture compounds into an appropriate solvent.Extraction processes include removal of soluble compounds from a solid matrix, then transfer the compounds from one liquid solvent to another liquid solvent.
4Principle of Extraction Extraction is a particularly effective means of separating organic compounds if one compound in the mixture can be chemically converted to an ionic form.The ionic form is soluble in an aqueous layer( polar layer) and can be extracted into it.Other non-ionized organic compounds in the mixture will remain dissolved in the non-polar solvent layer.Separation of the two layers results in the separation of the dissolved compounds.
5Principle of Extraction Example:The addition of sodium carbonate to the tea and coffee in the extraction process of caffeine.the tannins are acidic and sodium carbonate is a base, so when sodium carbonate is added to the tea water mixture, the acids are converted to their sodium salts which are highly soluble in water.ArO¯ Na⁺ + HCO3 ¯ → ArOH Na2CO3tannins tannins saltssoluble in water soluble in water andand chloroform insoluble in chloroform
6Principle of Extraction Caffeine is an alkaloid, an organic base. Sodium carbonate also a base, and it is added in the first extraction to make sure that the caffeine remains in the free base form (to prevent it from reacting with any acids that may be present).
7solvent Solvent selection: (Likes dissolve likes) Solvents differ in their extraction capabilities depending on their own and the solute’s chemical structureProperties of solventImmiscible or poorly miscible with the main solution. e.g. water/ether or water/ chloroformThe target compound dissolves well in the solvent.have low boiling point (reasonably volatile).
8Distribution coefficient distribution coefficient (partition coefficient) K:the ratio of the concentration of a single solute in two immiscible solvents.Partition functions with larger values result in more efficient extractions.Concentration in extractantConcentration in source solution
9Distribution coefficient Example:a solute that has a solubility of 8g /100mL of ether, and 2g /100mL of water.
10Extraction of Caffeine from Tea Leaves or coffee. The major components of tea leavesCellulose − the major structural material of all plant cells. Since cellulose is virtually insoluble in water it presents no problems in the isolation procedure.Caffeine − one of the major water soluble substances present in tea leaves. Caffeine comprises as much as 5% by weight of the leaf material in tea plants.Tannins − high molecular weight, water soluble compounds that are responsible for the color of tea.Flavonoid Pigments − water soluble colored compounds that are widely distributed in plant life
11caffeineCaffeine belongs to a group of compounds known as alkaloids. Alkaloids are a group of compounds that are found primarily in plants and contain basic nitrogen atom(s).
12caffeineThe major sources for caffeine are the seeds of the coffee plant , cola nuts, and Tea leaves.Caffeine acts as a stimulant. It stimulates the heart, respiration, the central nervous system, and is a vasodilator (relaxes the blood vessels) as well as a diuretic (increases urination).
13Extraction of Caffeine from Tea Leaves Procedure 1-Place 30 g of the tea leaves or tea bags in a 1000 ml beaker. Add 300 ml of distilled water and 5 g of sodium carbonate and stir the contents of the beaker with a glass rod.Or place 20g of coffee in 500ml beaker. Add 200ml distalled water and 5g sodium carbonate.Boil the beaker over direct flame or hot plate for 20 minutes.Cool the solution at room temperature.
14Extraction of Caffeine from Tea Leaves Procedure Ensure separating funnel valve shut. Using an ordinary funnel, pour the solution into the separating funnel.Extract the caffeine with four successive 25 ml portions of chloroform. Do not shake the separating funnel vigorously.Remove the lower layer from the separating funnel into 250 ml beaker through an ordinary funnel lined with filter paper and a drying reagent such as anhydrous sodium sulphate.Evaporate the combined chloroform extract to obtain a crud product .With a spatula, remove the solid left behind and mass it. This solid is principally caffeine.
15Extraction of Caffeine from Tea Leaves Procedure