Isolation, purification and characterization of alkaloid caffeine from tea leaves
Date Submitted: September 3, 2014
Caffeine is one of the main constituents of tea leaves. In this experiment, 0.0039 g of pure caffeine was isolated from tea leaves. This was done through solid-liquid extraction followed by multiple liquid-liquid extraction. Then crude material obtained was then purified by sublimation. The isolated caffeine was subjected to thin layer chromatography (TLC) together with a standard caffeine. The Rf value obtained for both isolated caffeine and standard caffeine was 0.24.
Keywords: solid-liquid extraction, multiple liquid-liquid extraction, sublimation, thin layer chromatography, percent caffeine
Many organic compounds are obtained from natural sources through isolation. In this experiment, caffeine is isolated from tea leaves. Caffeine belongs to a class of organic compounds isolated from plants called alkaloids. These nitrogenous compounds contain molecule that has purine ring system that plays an important role in living systems. Caffeine is one of the most widely used stimulants.It can increase the person's alertness, reduce drowsiness and fatigue. It also affects the blood circulation because the heart is stimulated thus, making the blood vessels relaxed (vasodilation). In addition, it also acts as diuretic. Caffeine constitutes as much as 5% by weight of tea leaves. Caffeine is also the natural constituent of coffee which contains less than 135 mg per cup and cola which contains 3.75 mg per ounce.
Tea leaves are not composed of caffeine alone. Tannins, cellulose, small amount of glucose, free amino acids, some proteins, residual pigments and saponins are compounds extracted along with caffeine into the tea. Cellulose is the main component of tea leaves and is insoluble in water. Tannins are phenolic compounds with high molecular weight, acidic behavior and soluble in water. Caffeine, like tannins is also soluble in water.
Caffeine can be extracted from tea leaves first through solid-liquid extraction which would then be followed by liquid-liquid extraction. Solid-liquid extraction is the method of extracting soluble constituents from a solid or semi-solid sample by means of suitable solvents. In this extraction, using hot water, insoluble cellulose will be separated from the more soluble caffeine.
Liquid-liquid extraction is the method of separating a substance from a mixture by dissolving one or more of the components in a solvent. This method must be done after solid-liquid extraction to isolate caffeine from tannins and other components in the tea. Caffeine and tannins have difference in solubility. Although caffeine is soluble in water, it is more soluble in organic solvent dichloromethane. On the other hand, when a basic salt is added in the water solution, tannins can react and form salt. These salts are insoluble in organic solvents but are soluble in water. Thus, caffeine can be isolated in the tea solution with dichloromethane, but the sodium salts of tannins will be remained in the aqueous solution.
Most substances in tea leaves are insoluble in organic solvent dichloromethane but, pigments such as chlorophylls and their oxidation products are both soluble in water and organic solvent. Although they are present in small amount, they are still extracted along with caffeine. Thus, extraction with dichloromethane yields crude caffeine. This crude material can be purified by sublimation. Sublimation is the process in which the sample goes directly from solid state to vapor state without passing the liquid state.
Organic chemists use an important technique called thin layer chromatography (TLC) for analysis and characterization of mixtures and reaction products. The pure caffeine extracted, together with a standard caffeine can be subjected to this technique to determine the retardation factor (Rf) value.
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 Extraction of caffeine from tea leaves. Retrieved August 2013 from: http://spot.pcc.edu/~chandy/241/CaffeineExtractionCH2CCl2.pdf
 Pavia, P.L...(et. al). (2005). Introduction to Organic laboratory techniques, 2nd ed. Belmont, CA: Thomson Learning, Inc.
 Palleros, D.R. (2000). Experimental Organic Chemistry. USA: John Wiley & Sons, Inc.
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