Using Solid Liquid Extraction Of Caffeine From Tea Leaves

867 WordsJul 13, 20164 Pages
The purpose of this experiment was to use solid-liquid extraction to isolate a crude sample of caffeine from tea leaves and then subsequently purify the isolated sample via sublimation. The two solvents used in the extraction were water and dichloromethane. In addition to caffeine, tea leaves also contain other compounds that must be dealt with including cellulose, proteins/pigments, tannins, and saponins. Cellulose is not soluble in water as a result of its high molecular weight and thereby does not dissolve in water during the boiling process. Proteins and pigments are highly soluble in water and thereby do not present any problems since caffeine is being extracted into the organic layer. Tannins are soluble in the organic layer and can become problems when trying to isolate just caffeine. To deal with Tannins, we add weakly basic CaCO3 during the boiling process so that the ester bonds in Tannins are cleaved thereby producing their corresponding calcium salts, which become water-soluble. Saponins cause increased solubility of organic molecules in the aqueous layer and are dealt with by salting out the aqueous layer so that it becomes more polar leading to decreased organic solubility in it. Moreover, saponins can cause emulsions to form because of their membrane like properties and this can be dealt with via centrifugation prior to each extraction. Following extraction of caffeine in dichloromethane, the organic solvent can be evaporated so that a crude sample of caffeine
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