In the Laboratory
The Extraction of Caffeine from Tea A Modification of the Procedure of Murray and Hansen Andreas Hampp Department of Chemistry and Biochemistry, University of California, Los Angeles, 405 Hilgard Ave, Los Angeles, CA 90095 According to the literature published, the “Extraction of Caffeine from Tea” is certainly one of the most common experiments in undergraduate laboratories. The extraction was generally done using chloroform (1–3), or methylene chloride (4–7), solvents known as possible human carcinogens. A recent publication by S. D. Murray and P. J. Hansen reports a less toxic alternative through the use of 1-propanol (8). However, in following the procedure given, we noticed that the crude caffeine obtained after evaporation of 1-propanol was highly contaminated with tannins and sodium chloride. In many cases we observed difficulties redissolving the brownish, sometimes oily residue for further purification. We introduced an additional cleaning/extraction step, which is commonly performed in organic synthesis. It consists of a wash with a 10% aqueous NaOH solution to extract tannins and sodium chloride from 1propanol and subsequent drying with sodium sulfate anhydrous prior to evaporation. The average yield of crude caffeine is unaffected and the product is obtained as a yellowish powder.
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This slight variation of Murray and Hansen’s procedure is currently used in our first-year chemistry laboratory classes and clearly shows a higher student success rate in the isolation crude caffeine. The experiment described here is performed in a three-hour lab period, which is followed by sublimation and characterization through melting point and infrared spectroscopy on a second day. Literature Cited 1. Helmkamp, G. K.; Johnson, H. W. Selected Experiments in Organic Chemistry, 2nd ed.; Freeman: San Francisco, 1968; pp 157–158. 2. O’Connor, R. The Freeman Library of Laboratory Separates in Chemistry; Birdwhistell, R. K.; O’Connor, R., Eds.; Freeman: San Francisco, 1971; Vol. 2. 3. Pavia, D. L.; Lampman, G. M.; Kriz, G. S.; Introduction to Organic Laboratory Techniques; Saunders: Philadelphia, 1976; pp 58–62. 4. Williamson, K. L. Macroscale and Microscale Organic Laboratory, 2nd ed.; Heath: Toronto, 1989; pp 130–133. 5. Mayo, D. W.; Pike, R. M.; Butcher, S. S. Microscale Organic Laboratory, 2nd ed.; Wiley: New York, 1989; pp 162–164. 6. Nimitz, J. S. Experiments in Organic Chemistry; Prentice-Hall: Englewood Cliffs, NJ, 1991; pp 61–62. 7. Landgrebe, J. A. Theory and Practice in the Organic Laboratory, 4th ed.; Brooks/Cole: Pacific Grove, CA, 1993; pp 381–383, 8. Murray, S. D.; Hansen, P. J. J. Chem. Educ. 1995, 72, 851–852.
Journal of Chemical Education • Vol. 73 No. 12 December 1996
