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Unformatted text preview: CHM 2201 Fall 2009 Department of Chemistry Organic Chemist ry Lab I Villanova University Page 1 of 4 Isolation of Caffeine from Tea Using Column Chromatography From Bell, Clark & Taber, pages 70 – 71 Carry out this experiment in your hood!! N N N N O O C H 3 CH 3 CH 3 Work in pairs and plan your work efficiently since Caffeine this lab can take 3 or more hours to complete. It is suggested that one person in the workgroup carry out part A (the tea extraction and adsorption of the tea extract onto silica gel) while the other person simultaneously starts with parts B (column preparation) and C (preparing the test tubes, obtaining the eluting solvents for the actual chromatography, and preparing the TLC plates which will be used for analysis of the TLC fractions). A. Extraction of Caffeine from Tea 1. Place 50 mL of the prepared tea solution in a 125 mL separatory funnel and add 20 mL of 5% aqueous HCl. (to help prevent emulsion formation) 2. Extract this mixture 4 times with 10 mL portions of methylene chloride (dichloromethane). IMPORTANT: methylene chloride is heavier than water. Do not shake the separatory funnel but vigorously SWIRL it (you may invert the separatory funnel to get better mixing during the swirling process) to help prevent the formation of an emulsion. REMEMBER: Vent the separatory funnel during the extractions to prevent pressure buildup! 3. Drain each of the above four methylene chloride extracts into a single dry 125 mL Erlenmeyer flask; make sure that there are not significant amounts of water drops in the methylene chloride extracts. If you see significant amounts of water in the combined methylene chloride extracts, place the combined extracts in a dry separatory funnel and carefully drain off the methylene chloride (being careful to keep the water in the separatory funnel) layer into another dry 125 mL Erlenmeyer flask. 4. Dry the combined methylene chloride extracts by adding 2-3 large spatula scoops of anhydrous magnesium sulfate and swirling the flask. After swirling the flask, the drying agent should be a loose and granular suspension (not sticking to the flask in chunks) in the methylene chloride; if not loose and granular, add another portion of magnesium sulfate, swirl and check to see if the newly added magnesium sulfate is loose and granular. Repeat the process until the newly added magnesium sulfate stays loose and granular. 5. To remove the magnesium sulfate from the combined methylene chloride extracts, filter the resulting mixture through a fluted filter paper placed in a funnel which goes into a dry 125 mL Erlenmeyer flask. 6. Add 0.2 g of silica gel and 1 or 2 boiling stones to the methylene chloride filtrate in the Erlenmeyer flask and evaporate the solvent by heating gently in the hood on a steam bath (See how to set up and use a steam bath described on page 4) to give a dry powder of your tea extract on silica gel. During the heating/evaporation process, constantly swirl the flask so that the solvent does not “bump” out of the flask.the solvent does not “bump” out of the flask....
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This note was uploaded on 02/20/2012 for the course CHE 118B taught by Professor Nasiri during the Winter '08 term at UC Davis.
- Winter '08