Caffeine Extraction from Tea Leaves

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  • Topic: Caffeine, Tea, Green tea
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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

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 220º and melted completely at 228º while the caffeine started to melt at 228º and completely melted at 231º.

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. 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. 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. [3]

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 sublimation refers to the process of transition of a substance from...
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