5A Isolation of Caffeine from Tea or Coffee

5A Isolation of Caffeine from Tea or Coffee - 5A Isolation...

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5A Isolation of Caffeine from Tea or Coffee Author: Holly Polk Instructor: Oleksandr Zhurakovskyi Organic Chemistry Lab 243A, Section 010 Date Work Performed: February 26 , 2009 Date Submitted: March 5, 2009 Abstract In this lab, caffeine is extracted from the structural components of tea leaves and purified by the process of sublimation. The total weight of recovered caffeine was 57mg, when Lipton claims that there is 55mg of caffeine in their tea bags, so there was a very high percent recovery of 103% from the caffeine. Since that number is not probable, there were most likely impurities from earlier steps in the experiment. The acquired melting point from the recovered caffeine was 227-230°C, which was comparable to the known literature value of 227-228°C.
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Introduction The objective of this lab is to isolate caffeine from tea leaves (or coffee) through a sequence of extractions and purify it by the means of sublimation (a process by which a solid is evaporated into a gas). Caffeine is a member of the class of compounds organic chemists call alkaloids which are nitrogen containing basic compounds that are found in plants. This experiment uses several techniques: separation, extraction, anhydrous drying, evaporation, and sublimation (Padias, 40, 41). Extraction and sublimation are two of the most important techniques in this lab. Because tea leaves are very complex, a sequence of extractions must be performed. Tea leaves contain: cellulose, tannins, pigments/chlorophylls , and caffeine . Although there is a complex mixture of compounds, they may be separated based on their solubility and acidity/basicity. Since caffeine is more soluble in dichloromethane (140 mg/ml) than it is in water (22 mg/ml), it readily dissolves in the dichloromethane. Since caffeine will be isolated with dichloromethane (a moderately polar solvent), it can be assumed that tannins have the highest polarity followed by pigments/chlorophylls, caffeine, then cellulose (these polarities were designated by the number of present carbonyl groups and overall dipole-dipole interaction). To aid in organic layer separation, potassium carbonate (to convert carboxylic acid to become water soluble) and dichloromethane are added to the collected liquid (heated tea) before centrifuging. The organic layer is then collected (on the bottom rather than the top due to dichloromethane density) and combined with anhydrous sodium sulfate to remove excess water without drying out the sample. This “dried” sample is then evaporated (to remove the dichloromethane and leave the collected crude caffeine). Then, the crude caffeine is prepared to be further purified by the means of a sublimation
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5A Isolation of Caffeine from Tea or Coffee - 5A Isolation...

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