Extraction of Caffeine from Tea Leaves
Extraction of Caffeine from Tealeaves Perez, Albert Solomon K. *; Quiambao, Marie Angela C;. Pascua, Hanna Harriette R. ; Patricio, Maria Roxanne DC. ; 2-Chemistry, Department of Chemistry, College of Science University of Santo Tomas Espana St. , 1015, Manila Abstract Caffeine is soluble in both water and organic solvents, solid-liquid extraction and liquid-liquid extraction were used in the experimentation process. Caffeine was extracted using hot water, however, due to its medium polarity; it was further separated from water soluble compounds using a polar non-protic solvent, dichloromethane (CH2Cl2).
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Sublimation was then used for the purification of the targeted compound. Based from the data collected, 5. 758g of tea leaves contains 3. 96% caffeine. After the purification process, 0. 2279g of caffeine was obtained from 0. 4948g crude extract with 46. 06% yield. Melting point determination was used to characterize the caffeine yielded. However, the melting point range of the caffeine collected (190°C -215 °C) was lower than the melting point of the accepted value (238 °C) which may be due to experimental errors committed in the extraction and washing process.
Introduction Tea has been consumed as a beverage for almost 2,000 years starting in China. It is the most widely consumed beverage after water . Their active participation in trade resulted in its introduction to Europe. The active component in tea is caffeine (C8H10N4O2). Caffeine belongs to an extensive class of compounds known as the alkaloids. Alkaloids are a diverse group of compounds that are found primarily in plants and contain basic nitrogen atom(s). The basic nature of these compounds makes them exists mostly as salts.
Many alkaloids have profound effects on the nervous system and acts as a mild stimulant examples are other well-known alkaloids such as morphine, strychnine, quinine, ephedrine, and nicotine. Aside from being a mild stimulant, caffeine is one of the most promising organic compounds in medicine, in a study by Miura, T. et al. , green tea extracts showed lowering in blood pressure of a mice with diabetes type 2 and thus a plausible treatment for diabetes. However, caffeine may be associated with serious ventricular arrhythmias in susceptible people.
Caffeine may increase beat-to-beat heart rate variability and also QT interval variability during rapid eye movement sleep. Caffeine cannot be obtained directly; every pot of coffee or cup of tea involves solid/liquid extraction, the extraction of organic compounds from solid ground beans or leaves using hot water as the liquid. The lower molecular weight polar molecules such as caffeine dissolve in the hot water and are removed from the high molecular weight water-insoluble cellulose, protein, and lipid materials.
Over 200compounds, some in only trace quantities are extracted from the solid into a cup of coffee or tea. Figure 1 shows the chemical structure of caffeine. [pic] Figure1. Caffeine While solid-liquid extraction is the most common technique used to brew beverages and isolate natural products, liquid/liquid extraction is a very common method used in the organic laboratory. Organic reactions often yield a number of by-products, some inorganic, some organic. Also, since they do not go to 100% completion, some starting material is also often present at the end of an organic reaction.
Liquid-liquid extraction is often used as the initial step in the work-up of a reaction, before final purification of the product by recrystallization, distillation or sublimation. Varying extracts from various plants have been used as teas, potions, medicines and poisons. However, these extracts can contain a mixture of many different chemicals, often only one or few are responsible for the activity of the extract. The objective of this experiment is to isolate, purify and characterize caffeine from tea leaves. Moreover, to calculate the percent yield of caffeine.
Results and Discussion Extraction of caffeine from tea leaves through solid-liquid extraction using water bath would cause the tea leaves to swell and release caffeine and other compounds such as tannins. To further separate caffeine from other soluble compounds, an organic solvent, Dichloromethane (CH2Cl2) was used. Dichloromethane (CH2Cl2) selectively extract caffeine from the tea extract by separating it from the other organic compounds and leaving them suspended in water. Table1. Relative Weights of Products Yield of Products | |Brand of tea leaves |Nature’s Pride | | | | |Extraction | |Weight of beaker |28. 6880g | |Weight of beaker |34. 4460g | |+ tea leaves | | |Weight of tea leaves |5. 58g | |Weight of evaporating dish |115. 7196g | |Weight of evaporating dish |116. 2144g | |+ crude caffeine | | |Weight of crude caffeine |0. 4948g | | | | |Purification | |Weight of empty vial |32. 2127g | |Weight of empty vial |32. 406g | |+ caffeine crystal | | |Weight of caffeine crystal |0. 2279 | Extraction uses the solubility differences of these molecules to selectively draw the product into the organic layer. Liquid-liquid extractions using 20mL dichloromethane was done three times to ensure the highest percentage of caffeine separation. All portions of dichloromethane was mixed and was washed with 20mL 6M NaOH in the separatory funnel, to remove acidic content from the solution that may have remained after the extraction with dichloromethane.
The ‘washed’ dichloromethane solution was filtered through a filter paper containing anhydrous Na2SO4 to further dehydrate the solution, hydrating the Na2SO4 into its hydrated form Na2SO4·H2O. Table 1 shows the different weights of the sample obtained through extraction and purification before its characterization. Crude caffeine, about 0. 4948g was obtained through recrystallization, and was purified. Purification was facilitated by sublimation with an air bath to gather the pure crystalline caffeine. The crystalline caffeine was found to be 0. 276g in weight. The percent recovery and percent caffeine can now be computed through: % recovery = [pic] % caffeine = [pic] % recovery = [pic]% caffeine = [pic] % recovery =46. 06%% caffeine = 3. 96% To characterize the sample, determination of the melting point was used. Table 2 summarizes the results of melting point determination of the sample and standard caffeine subjected to an oil bath consisting of cooking oil at 150 degrees celsius. Table2. Melting Point Determination |Melting Points (?
C) | |Sample caffeine |Standard caffeine | | | | |T1 | |190 degrees |225 degrees | | | | |T2 | |215 degrees |228 degrees | | | | |190-215 degrees |225-228 degrees | The accepted value for the melting point of caffeine is 238? C . The experimentally determined temperature for the sample caffeine was very low in comparison to the standard and the accepted value. The standard caffeine had close values and a smaller melting point range. Errors could lie in between the melting process, as the standard underwent some thermal decomposition evident in the slight change in the color of the sample while melting. The temperature obtained explicitly shows the presence of impurities on the sample caffeine, as the presence of non-volatile solutes owers the temperature and increases the melting point range of a sample. Imprecise reading and observations could have been one of the reasons for the slightly lower melting point temperature readings for the standard caffeine. Experimental For the extraction of caffeine, commercialized tea bags (3) were used as a source of tea leaves. Tea leaves were removed from the bags and were weighed. After weighing the tealeaves, solid-liquid extraction was done using 100-mL water and was allowed to boil for 5 minutes. The sides of the flask were then cooled in a running tap water for 2 minutes. An ice cube was mixed in the tea extract to facilitate cooling to room temperature.
The tea extract was transferred in a separatory funnel containing 20-mL of dichloromethane to facilitate liquid-liquid extraction of caffeine. The CH2Cl2 was found to be in the lower layer and was drained into a clean flask. The remaining solution in the separatory funnel was again treated with 20-mL CH2Cl2 twice to further extract the remaining caffeine. All CH2Cl2 fractions were combined. All of the CH2Cl2 was returned to the separatory funnel and that was washed with 20-mL 6M NaOH solution. After washing, The CH2Cl2 layer was drained into a flask through a funnel with a fluted filter paper containing half spatula of anhydrous sodium sulphate to remove the remaining water content.
The CH2Cl2 was subjected in a water bath to further concentrate the extract. The crude caffeine was weighed and the numerical value was recorded. For the purification process, the crude caffeine was transferred into a filter tube with a fitted inner test tube which served as the ‘cold finger’ and was placed in a hot air bath. The crude caffeine was allowed to sublime to gather crystalline caffeine at the bottom of cold finger tube. The cold finger was constantly refilled with ice water to facilitate sublimation. The crystalline caffeine was scraped off the cold finger tube and was placed into a vial. For the characterization of crystalline caffeine, the caffeine crystals were grinded into a very fine powder.
A micro capillary tube was sealed at one end which acted as a micro test tube. The open end of the micro test tube was dipped into the vial containing pulverized caffeine crystal and was dropped inside a long glass tube until the sample reached a height of 0. 5-1cm. The same procedure was done on the standard caffeine sample. For the melting point determination, the two samples were secured in both sides of a thermometer. The thermometer was dipped into a beaker containing cooking oil heated at 150 degrees (oil bath). The temperature range between the first appearance of liquid within the sample until the disappearance of the last traces of solid was recorded. Conclusion
The extraction of caffeine is a critical experiment, as it uses different chemistry principles such as solubility rules and a substance’s physical properties. The percent yield of 3. 96% is a reasonable finding since green teas are found to contain only 3-5% of its dry weight. Impurities which caused the melting point lowering of the sample could have resulted from experimental errors and could have occurred during the extraction and washing processes. In addition to experimental errors, the presence of soluble tannins in tea leaves complicates the isolation of caffeine, this could have been fixed in the solid-liquid extraction state through the addition of CaCO3 to separate tannins and keep them suspended in the water.
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