Extraction of Caffeine from Tea Part I 1, Schemes and Mind Maps of Chemistry

Download Extraction of Caffeine from Tea Part I 1 and more Schemes and Mind Maps Chemistry in PDF only on Docsity! Org Chem I Experiment 5 - Extraction of Caffeine from Tea Part I 1 Tea and coffee have been popular beverages for centuries, primarily because they contain the stimulant caffeine. It stimulates respiration, the heart, and the central nervous system, and is a diuretic (promotes urination). It can cause nervousness and insomnia and, like many drugs, can be addictive, making it difficult to reduce the daily dose. A regular coffee drinker who consumes just four cups per day can experience headache, insomnia, and even nausea upon with drawl from the drug. On the other hand, it helps people to pay attention and can sharpen moderately complex mental skills as well as prolong the ability to exercise. Caffeine may be the most widely used and abused drug in the United States. During the course of the day an average person may unwittingly consume up to a gram of this substance. The caffeine content of some common foods and drugs is given in table below. Caffeine Content of Common Foods and Drugs Espresso 120 mg per 2 oz Coffee, regular, brewed 103 mg per cup Instant coffee 57 mg per cup Coffee, decaffeinated 2 to 4 mg per cup Tea 30 to 75 mg per cup Cocoa 5 to 40 mg per cup Milk Chocolate 6 mg per oz Baking Chocolate 35 mg per oz Coca-Cola, Classic 46 mg per 12 oz Jolt Cola 72 mg per 12 oz Anacin, Bromo-Seltzer, Midol 32mg per pill Excedrin, Extra Strength 65 mg per pill Dexatrim, Dietac, Vivarin 200 mg per pill Dristan 16 mg per pill No-Doz 100mg per pill Caffeine belongs to a large class of compounds known as alkaloids. These are of plant origin, contain basic nitrogen, often have a bitter taste and complex structure, and usually have physiological activity. Their names usually end in “ine”; many are quite familiar by name if not chemical structure-nicotine, cocaine, morphine, strychnine. Tea leaves contain tannins, which are acidic, as well as a number of colored compounds and a small amount of undecomposed chlorophyll (soluble in dichloromethane). To ensure that the acidic substances remain water soluble and that the caffeine will be present as the free base, sodium carbonate is added to the extraction medium. The solubility of caffeine in water is 2.2 mg/mL at 25°C, 180 mg/mL at 80°C, and 670 mg/mL at 100°C. It is quite soluble in dichloromethane, the solvent used in this experiment to extract the caffeine from water. “This Caffeine Extraction lab is Tea-riffic!” Merrit DeBartolo, Fall 2002 N C C C N C N CH N O CH3 CH3 O H3C Caffeine Org Chem I Experiment 5 - Extraction of Caffeine from Tea Part I 2 Caffeine can be extracted easily from tea bags. The procedure one would use to make a cup of tea - simply “steeping” the tea with very hot water for a few minutes - extracts most of the caffeine. Since caffeine is white, slightly bitter, odorless, crystalline solid, it is obvious that water extracts more than just caffeine. When the brown aqueous solution is subsequently extracted with dichloromethane, primarily caffeine dissolves in the organic solvent. Evaporation of the solvent leaves crude caffeine, which on sublimation yields a relatively pure product. When the concentrated tea solution is extracted with dichloromethane, emulsion can form very easily. There are substances in tea that cause small droplets of the organic layer to remain suspended in the aqueous layer. This emulsion formation results from vigorous shaking. Insoluble Cellular Material Tea (caffeine) Aqueous Na2CO3 Tannin and organic salts CH2Cl2 Caffeine Non-polar molecules N N N N O CH3 CH3 O H3C Caffeine Brewing and filtration Liquid/liquid extraction Evaporate CH2Cl2 Org Chem I Experiment 5 - Extraction of Caffeine from Tea Part I 5 D. Sublimation of Caffeine Sublimation is a fast and easy way to purify caffeine. Set up the apparatus depicted below. Use the rest of your crude caffeine left over from part C. If you do not have much substance, combine yours with your hood-mate. Place the dry caffeine powder at the bottom of the flask. Fill the test tube with crushed ice. The bottom of the test tube should rest about 1 cm from the bottom of the filter flask. The test tube and flask should be clean and dry. Sublime the crude caffeine at atmospheric pressure by placing the flask directly on a pre- heated hot plate. Caffeine melts at 238°C and sublimes at 178°C. Collect your sublimed caffeine. Put this in a labeled vial and hand it in for analysis. Surfing the Web-------------------------------------------------------------------------------------- http://domin.dom.edu/faculty/jbfriesen/chem253lab/caflab/caflab.htm Several photos of the Dominican University “extraction of caffeine from tea” by those brave souls who have gone before you. http://ull.chemistry.uakron.edu/organic_lab/cola/ The extraction of caffeine from 10 mL of cola syrup (Experiment 4) is very clearly demonstrated in 14 color photos. Org Chem I Experiment 5 - Extraction of Caffeine from Tea Part I 6 Checklist for completing the "Prelab" section: (refer to Laboratory Syllabus for complete directions) ____ Title and date ____ Purpose. Refer to procedure Physical constants. Create a table of physical constants, solubility, and safety data for: ____ caffeine ____ dichoromethane (methylene chloride) ____ methanol ____ sodium carbonate ____ References Structures and equations. (none) ___ Flowchart. Refer to "Procedure" ___ Calculations. If you assume that one teabag makes one cup of tea, about how much caffeine would you expect to extract in this experiment? (Refer to the table on the 1st page.) Show your calculations. ____ Define the following terms as they apply to HPLC: 1) peak, 2) retention time, 3) adsorbent, 4) eluant ____ Safety Question: Dichloromethane is considered to be a volatile respiratory irritant. What two precautions may you take to keep dichloromethane vapors out of your lungs? Tea, although an Oriental, Is a gentleman at least; Cocoa is a cad and coward, Cocoa is a vulgar beast. G. K. Chesterton, The Song of Right and Wrong Org Chem I Experiment 5 - Extraction of Caffeine from Tea Part I 7 Experimental Observations and Data: Hand in a copy of your experimental observations and data before you leave lab. Experimental Observations. ___ What was the appearance of each reagent? ___ Mass of Na2CO3 used ___ What was the volume of tea at the beginning of your extractions? ___ What did extractions look like? ___ Have you clearly labeled parts A, B, C & D? ___ What were the results of TLC? Calculate Rf values. Trace slide into notebook. Label clearly ___ How did the crude caffeine differ from the sublimed? ___ Did you record interesting sights and smells? Data ___ Record the mass of your tea bags. ___ Record the mass of your crude caffeine. Lab Report Checklist: Results. ___ Calculate the percent yield of caffeine from tea. Show your calculations. (mass of crude caffeine x 100 /mass of tea leaves) ___ Report your Rf values from your TLC experiment. ___ Compare the “student sample” UV spectrum with the UV spectrum of pure caffeine. Both can be found on the chem253lab webpage. What are at least two similarities? What are at least two differences? ___ Compare the “student sample” HPLC chromatogram with the HPLC chromatogram of pure caffeine. Both can be found on the chem253lab webpage. What are at least two similarities? What are at least two differences? Discussion and Conclusion. ____ How did your yield compare with your calculations in the prelab? Explain why your observed results (at least 2 reasons) might have been different than the “theoretical yield.” ____ What are two conclusions that you can draw from your TLC, HPLC, and UV data? _____ Green Question: Dichloromethane is generally nasty stuff. What could be used to replace dichloromethane in this procedure? Hint: Where does decaffeinated coffee come from? Give sources please. _____ Are you a caffeine user? What effect does caffeine have on you?