Resumen de The Extraction of Caffeine from Tea:: A Modification of the Procedure of Murray and Hansen
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.
