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Isolation of Caffeine From Tea

Isolation of Caffeine From Tea. Experiment 12A (4 th ed.) Experiment 11 (3 rd ed.). Read Before Class. 4 th ed.—Experiment 12 Techniques 12 & 17 3 rd ed.—Experiment 11 Techniques 7 & 16. Overview. Tea Leaves  1 Cellulose, 2 Caffeine, 3 Tannins

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Isolation of Caffeine From Tea

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  1. Isolation of Caffeine From Tea Experiment 12A (4th ed.) Experiment 11 (3rd ed.)

  2. Read Before Class • 4th ed.—Experiment 12 • Techniques 12 & 17 • 3rd ed.—Experiment 11 • Techniques 7 & 16

  3. Overview • Tea Leaves  1Cellulose, 2 Caffeine, 3Tannins • Glucose polymer; not soluble in H2O • Alkaloid compound; soluble in H2O, but more soluble in CH2Cl2 • Phenolic compounds; all are potentially soluble in H2O, and some undergo hydrolysis in H2O

  4. Overview • Tannins that are hydrolyzed when mixed with H2O produce glucose + gallic acid. • Adding Na2CO3 makes the acidic solution basic & converts tannins & gallic acid to H2O-soluble sodium salts. • This opens the door for a separation of caffeine from the other components via extraction by adding CH2Cl2 to the aqueous solution. • Crude caffeine can then be isolated by evaporating off the CH2Cl2 solvent and further purified by sublimation or crystallization.

  5. Procedural Notes Preparing Your Tea Solution • Get the mass of your tea leaves from me. • Be very careful not to rupture the tea bag when rolling it with your stir rod. • You want to keep your tea leaves submerged during the heating process, so heat a separate beaker of hot water along with your tea solution—this water will be used to replenish the supply of water in the reaction beaker that has evaporated & also for heating your flask later. • Keep your solution temperature around 90oC (just below standard b.p. of water) to avoid boiling over of the solution.

  6. Procedural Notes Extraction & Purification • Be sure to vent the centrifuge tubes frequently upon addition of Na2CO3 to avoid pressure buildups. • If the CH2Cl2 and water aren’t separating efficiently after shaking the tubes, centrifuge them for 1-2 minutes to break up the emulsion.

  7. Analysis • Perform the following analyses on both your crude and pure products: • % Recovery (NOT Yield!!) • Melting Pt. (~236oC)

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