Lecture Lab E - Isolation of Caffeine February 27, 2009...

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Isolation of Caffeine February 27, 2009 Extraction
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N N N N O O Alkaloid-Nitrogen containing compound isolated from plants
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Caffeine blocks adenosine in order to keep us from falling asleep. It may also be used to alleviate pain, migraine headaches, and asthma. Lethel in very high doses, such as what would be found in 80-100 cups of coffee drunk rapdidly. It is found naturally in many plants such as coffee and tea. Coffee can be decaffeinated by extracting the caffeine with dichloromethane. The caffeine obtained from decaffinating coffee is used to add to other products. Caffeine Dredges
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Cellulose Caffeine Chlorophyll Tannins boiling H 2 O Filter Cellulose Caffeine Chlorophyll Tannins Water Practical hint : Cover beaker with watch glass while boiling tea You need to use 4 tea bags which you obtain the exact mass of
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Extraction -Compounds partition between two layers based on relative solubilities RECALL: What are the forces that control solubility -Van der Waals Forces -Dipole-Dipole forces -Hydrogen bonding Like dissolves like-oil and water do not mix Reaction mixtures can be separated in this way Water-salts, ions Organic-most organic compounds
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Solubility of Caffeine Dichloromethane H 2 O Polar, organic solvent Hydrogen bond donor/acceptor Does not dissolve a lot of organics N N N N O O Polar, organic compound with H bond acceptor sites 2.2 g/100 mL 10.2 g/100 mL
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How much do we extract? Partition Coefficient er ilityinwat so aniclayer ilityinorg so K lub lub = PROBLEM: You have 1.0 grams of a compound dissolved in 100 mL of water. If the partition coefficient is 5, how much will you extract into 25 mL of dichloromethane? 100 1 25 5 x x - = X=.55 grams
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PROBLEM:If you are going to use 50 mL of dichloromethane, would you be better off with 1 50 mL extraction of 2 25 mL extractions? 100
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Lecture Lab E - Isolation of Caffeine February 27, 2009...

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