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 1-propanol 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.
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.
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