exp4w08

exp4w08 - Experiment 4: Isolation and Characterization of...

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Experiment 4: Isolation and Characterization of the Natural Product Caffeine (Solid-Liquid Extraction, Subli- mation) Mohrig, Chapter 12 In this experiment, the techniques of solid-liquid extraction and liquid-liquid extraction will be used to isolate caffeine from tea leaves. A new purification technique, sublimation , will be used to perform the final purification. The sublimation process is used by some color printers. Caffeine is a member of the class of natural products called alkaloids, which contain a ni- trogen atom. Other members of this class include morphine, mescaline, and strychnine. The biological activity of these compounds has led to their thorough investigation by many different disciplines. Caffeine possesses the oxidized skeleton of purine, a related compound which is a constituent of DNA (see above). Caffeine is found in many plants, with coffee and tea being the most familiar. A cup of coffee or tea provides a 25 to 100- mg “dose” of caffeine, which stimulates the central nervous system. Given the usual dosing method it should not surprising that caffeine is soluble in hot wa- ter. Caffeine is also soluble in dichloromethane, and can be isolated using a process called solid-liquid extraction . This isolation procedure assures that ionic species and non- organic materials remain in the aqueous layer and takes advantage of the swelling caused by water in the tea leaves. Simply extracting the tea leaves with dichloromethane directly would prove fairly ineffective. The sodium carbonate (Na 2 CO 3 ) added to the water dur- ing the “steeping” stage is to insure that the caffeine (a base) is not protonated by any of the organic acids in the tea. Thus, with the organic acids sequestered in the aqueous layer as their corresponding carboxylate salts, the caffeine will be free to dissolve in dichloro- methane while the carboxylate salts will not (see Experiment 3). The caffeine supplied by extraction is fairly pure. However, sublimation will further purify the material separating it from tannins, pigments, and other natural products of tea. Procedure
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This note was uploaded on 04/07/2008 for the course CHEM 6a taught by Professor Pettus during the Winter '07 term at UCSB.

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exp4w08 - Experiment 4: Isolation and Characterization of...

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