Extraction of Caffeine from Tea Leaves

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The solubility of caffeine in water is 2.2 mg/mL at 25°C, 180 mg/mL at 80°C, and 670 mg/mL at 100°C [5].

Although caffeine is soluble in water, it is much more soluble in the organic solvent methylene chloride. Caffeine can be extracted from the basic tea solutions with dichloromethane (also known as methylene chloride), but sodium salts of gallic acid and the tannins remain in the aqueous layer.

The brown color of a tea solution is due to flavonoid pigments and chlorophylls and to their respective oxidation products. Although chlorophylls are soluble in methylene chloride, most other substances in tea are not. Therefore, the dichloromethane extraction of the basic tea solution removes nearly pure caffeine. The dichloromethane is easily removed by evaporation to leave the crude caffeine. The caffeine is then purified by sublimation, but an attempt to sublime caffeine directly from tea leaves is also unsuccessful [5].

Chromatography is used to separate mixtures of substances into their components. In this case, it is used to determine the purity of the crude caffeine. The retardation factor (Rf) value pertains to the ratio of the distance travelled by the center of a spot to the distance travelled by the solvent front. In the thin-layer chromatography experiment, crude caffeine showed multiple spots. This indicates that the extraction process probably made errors in heating and separation, contamination, or overloading in the silicon strips.

Conclusion

The experiment successfully isolated caffeine from tea leaves, but not absolutely purified it due to some errors. The crude caffeine is has an Rf value of 0.56 with some impurities visible. The percentage of the caffeine of tea leaves is 0.076%.

Reference

- Caffeine. (n.d.). Retrieved February 27, 2017, from http://hprc-online.org/dietary-supplements/dietary-supplement-classification-system-1/class-4-supplements/copy2_of_branched-chain-amino-acids

- Alkaloid. (n.d.). Retrieved February 27, 2017, from http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/alkaloid

- Caffeine -- History, Chemical and Physical Properties and Effects. (n.d.). Retrieved February 27, 2017, from http://www.scienceofcooking.com/caffeine.htm

- Pavia, D. L., Lampman, G. M., Kriz, G. S., & Engel, R. G. (2016). A small scale approach to organic laboratory techniques (Fourth edition.). Australia: Cengage Learning.

- Williamson, K. L., & Masters, K. M. (2012). Macroscale and microscale organic experiments (Sixth edition.). Boston, MA: Cengage Learning.