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Extraction of Caffeine from Tea Leaves Marc Tugaoen, Kristine Vanzuela, Rafael Villanueva, Justeen Wong Department of Chemistry, University of Santo Tomas, Manila, Philippines Abstract This experiment has been divided into 4 set-ups, first was the solid-liquid extraction, next was the liquid-liquid extraction, then the sublimation and last was the melting point determination.
The solid-liquid and liquid-liquid extraction were both done during the first meeting, the DCM layer was filtered and dried in the evaporating dish and kept inside the locker.
The dried was light green, somewhat powdery flakes and was rough, this was purified through sublimation. The %yield of the caffeine was 0. 11%. The last part was determining the melting point of the pure caffeine collected, standard started to melt at 220? and melted completely at 228? while the caffeine started to melt at 228? and completely melted at 231?.
Introduction
The objectives of the experiment are to a. isolate, purify and characterize caffeine from tea leaves and to b. calculate the percentage yield of caffeine. The active ingredient in the tea and coffee is the caffeine, which is an alkaloid.
Alkaloids contain nitrogen and have properties of an organic amine base. Caffeine has a mild stimulating effect on the central nervous system. Caffeine belongs to the family of xanthine, which is known as stimulants. Caffeine is the most powerful xanthine because of its ability to increase alertness, put off sleep and increase ones capacity for thinking.
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It also relaxes blood vessels and increases urination. Other than tea leaves, caffeine can also be found in coffee, cocoa beans and kola nuts. Tea leaves consist mostly of cellulose, caffeine, and a small amount of chlorophyll.
Theoretical Yield Of Caffeine
The solubility of caffeine in water is 22 mg/ml at 25·C, 180 mg/ml at 80·C, and 670 mg/ml at 100·C. [1] There have been several concerns about the health risks of caffeine, although scientists have already said that normal consumption of caffeine doesn’t increase health risks. Many consumers still try to avoid caffeine, and because of these reason that decaffeinating coffee and tea has been an important industrial process. [2] Extraction is the technique we use to separate organic compounds from a mixture of compounds. It is the process of obtaining mixture or compound through chemical, physical and mechanical means.
Results and Discussion
In order to extract the caffeine from the tea leaves the solid-liquid extraction and liquid-liquid extraction were done first. During the solid-liquid extraction of caffeine from the tea leaves water was used because it’s cheap and nontoxic. Caffeine is only slightly soluble in hot water, and nearly insoluble in cold water, making it easy to get it to partition into a better solvent [4]. The aqueous layer was added with the dichloromethane or CH2Cl2 to easily extract caffeine since it’s more soluble in CH2Cl2.
To make sure that the solvent moves in all the tea leaf particles to extract caffeine, the separatory funnel was gently shaken. The stopcock was also slightly opened to let out any pressure. Sodium hydroxide was used to make sure that other substances, which are slightly soluble to dichloromethane, are eliminated by converting them to their salts that remain in the water [5]. The boiled tea leaves had two layers the aqueous and the CH2Cl2 layer, and these two were separated, this is the liquid-liquid extraction part. The liquid-liquid extraction resulted in a CH2Cl2 layer which was kept in the evaporating dish and dried.
Fig. 1 CH2Cl2 Layer (lower) and Aqueous Layer (upper) Fig. 2 Filtered DCM layer in an evaporating dish The crude caffeine was colored light green, somewhat powdered flakes and had a rough texture. Fig. 3 Dried DCM layer According to Wikipedia. org sublimation refers to the process of transition of a substance from the solid phase to the gas phase without passing through an intermediate liquid phase. Sublimation process was done to purify the crude caffeine; this was a delicate part because we must be careful in handling the test tube for the purified caffeine might fall from its attachment into the test tube.
The purified caffeine was colored white, fine, and also somewhat powdery and flakey. Fig. 4 Purified caffeine during sublimation Table 1. Characteristics of Crude and Purified Caffeine| | Color| Appearance| Size| Crude| Light green| Powdery, flakes| fine| Purified| White| Powdery, flakes| fine| The last part was the melting point determination. In this part we are able to tell the purity of the caffeine through the range of the melting point. Table 2. Melting point of Caffeine and Standard| | T1| T2| T1-T2| Caffeine| 228| 231| -3| Standard| 220| 228| -8|
Based on the result caffeine is more pure than the standard because the range of its melting point is less compared to the standard. Table 3. Weight of Tea Leaves and Pure Caffeine| Tea leaves| 5. 3692g| Vial w/ cap| 29. 6286g| Vial w/o cap| 27. 8898g| Vial (w/cap) and Caffeine| 29. 6343g| Caffeine| 0. 0057g| Based on the data above the percent yield we got was 0. 11% Experimental Three teabags were opened; tea leaves were combined and weighed. After weighing the tea leaves were returned in the tea bags and were secured with strings and staple wire. Teabags were then boiled in 100ml water for 5 minutes.
Fig. 5 Boiling tea leaves Fig. 6 Boiled tea The side of the flask was cooled in running water for 2 minutes. Then the ice cube was mixed in the teas extract cooling to room temperature. The tea extract was then transferred in the separatory funnel which has 20ml of CH2Cl2. Separatory funnel was gently shaken in an upside down manner and the stopcock was also opened a bit to release pressure. The CH2Cl2, lower layer was drained into a clean flask. This extraction was done twice. Then all CH2Cl2 portions were combined, the aqueous layer was discarded.
The combined CH2Cl2 was returned into the separatory flask; 20ml of 6M NaOH was added. The aqueous layer was discarded and the CH2Cl2 was put in an evaporating dish, the top was covered with aluminum foil which has some perforations, and it was kept in the locker to let it dry. Fig. 7 Tea extract being transferred into the separatory funnel The next step was the sublimation, to purify the crude caffeine. The crude caffeine was transferred in a filter tube with a fitted inner test tube which served as the ‘cold finger’; this was put into a hot air bath for about 35 minutes.
The cold finger was constantly filled with ice water. Fig. 8 Sublimation set-up, hot air bath The inner tube was carefully removed, the caffeine clinging into the cold finger was scraped off kept in a vial and weighed. The last procedure was the melting point determination. In this part, first the caffeine was grinded into a very fine powder. An end of a capillary tube was sealed by heating it, while rotating at 45? angle from the blue portion of the Bunsen burner flame. Using the open end of the capillary tube, pulverized caffeine crystal was scoop, and the height was 0. 5cm.
To pack the caffeine well at the bottom of the capillary tube, we let it fall inside a 1m glass tubing. Once it was well packed it was fastened with the thermometer and standard using a rubber. The thermometer was clamped and dipped into a beaker filled with cooking oil. It was heated using the Bunsen burner and a loop of #12 copper wire was used to make sure the heat of the cooking oil is distributed; we also made sure that the capillary tube did not directly touch the beaker so it wouldn’t burn. The melting point of the standard and the caffeine was observed and recorded.
Fig. 9 Cooking oil stirred with copper wire to distribute heat Appendix %yield = wt. caffeine (g)wt. tea leaves g x 100 %yield = 0. 0057g5. 3692g x 100 %yield = 0. 11%
References:
[1] http://www. angelfire. com/blog/caffeinechem/
[2] http://www. spot. pcc. edu/~chandy/241/CaffeineExtractionCH2CCl2. pdf
[3] http://www. scribd. com/doc/35716872/Extraction-of-Caffeine-from-Tea-Leaves
[4 ]http://answers. yahoo. com/question/index? qid=20090721101813AALFlRu
[5] Garcia, G. (2005). Laboratory Experiments in Organic Chemistry. University of Santo Tomas, Manila.
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