Extraction of Caffeine from Tea Bags

Topics: Caffeine, Tea, Black tea Pages: 7 (2408 words) Published: June 20, 2013
Extraction of caffeine from tea bags

Caffeine extraction from the commercial tea leaves (Lipton Yellow Label Tea) that was done is multiple extraction. 4 tea bags   were used in the experiment; tea leaves were weighed having 8.5333 grams. The leaves were boiled in a beaker with 150ml of water; the aqueous tea extract was transferred in a seperatory funnel mixed with DCM (20ml), done thrice. The DCM layer was washed with 20ml 6M NaOH in the seperatory funnel; the organic layer was dried with anhydrous Na2SO4. The dried organic layer turned into crude caffeine was purified in a sublimation set-up. A capillary tube was used to insert the pure caffeine to determine its melting point, having 228°C - 229°C. The purified caffeine from the sublimation set-up was weighed having 0.0007g; using the wt. of the sample and the wt. of the pure caffeine, the %yield was determined, 8.20 x 10 -3 %. It was noticed during the steps of the experiment involving the electronic scale that the number displayed never seemed to reach equilibrium. Even when the furniture containing the scale was closed and no one was moving nearby, the number on the display continued to fluctuate within a range of approximately 0.01 g. Thus, even though the Caffeine was massed at 0.109 g, it could actually have been anywhere between 0.099 g and 0.119 g. It is also possible that some Caffeine was lost during the use of the separatory funnel. To insure a pure result, the separatory funnel was not emptied completely of the organic layer. Almost 1 cm of organic layer was left in the funnel after each release. Every time the solution was transferred from one beaker to another, some Caffeine could have been left behind coating the container. Finally, some Caffeine might have been lost or destroyed during the evaporation process. This experiment has been described by one source as "a popular second-year organic experiment." Since the experimenter is currently working with a high school level of chemistry knowledge, it should not be surprising that some of the theory behind this experiment has proven confusing. It is believed that the experiment was carried out to the best of the experiments ability, however it is possible that with more experience and by using more sophisticated equipment, a more satisfactory result might have been obtained.

Caffeine is soluble in boiling water and as a result it is easily extracted from tea bags by steeping in hot water. This process leaves behind the water insoluble portions of the tea bag. However, water extracts more than just caffeine, so a final separation is done with an organic solvent that will dissolve primarily caffeine. The organic solvent used in this experiment is Dichloromethane (CH₂Cl₂). Dichloromethane is less polar than water and this difference in polarity allows the separation. Extraction of the tea with the Dichloromethane, followed by evaporation of the organic solvent leaves crude caffeine, which on sublimation yields a relatively pure product. Sublimation is the transition of a substance from the solid phase directly to the gas phase without undergoing intermediate liquifications. This process is preferred over recrystallization because it is better at removing impurities. The objectives of the experiment are to isolate, purify and characterize caffeine from tea leaves. The caffeine must be also purified, by using the sublimation set-up in the latter part of the experiment. The experimenters also need to determine the purity of caffeine by using the determined melting point.

Caffeine is the compound that is responsible for the stimulating action of coffee and tea. It is an example of an alkaloid; a group of organic compounds containing nitrogen. They are produced by plants and have physiological actions. Chemically, they are weak organic bases. Coffee beans contain less caffeine than tea leaves when weighed dry, but a serving of coffee contains roughly twice the caffeine of tea...

References: http://www.oxford.net/~mavarod/portal/school/caffeine.html
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