Department of Biological Sciences, College of Science
University of Santo Tomas
España, Manila, 1028
Caffeine is a white crystalline xanthine alkaloid that acts as a stimulant drug. Caffeine is found in varying quantities in the seeds, leaves, and fruit of some plants. It is most commonly consumed by humans in infusions extracted from the seed of the coffee plant and the leaves of the tea bush, as well as from various foods and drinks containing products derived from the kola nut. The water soluble materials in the tea leaves are extracted into hot water. The hot solution is allowed to cool and the caffeine is then extracted from the water with dichloromethane (methylene chloride), which is an organic solvent that is insoluble in water. Since caffeine is more soluble in dichloromethane than it is in water, it readily dissolves in the dichloromethane.
This experiment is aims to isolate crude caffeine from tea leaves. The purity of caffeine is determined through melting point determination, the comparison of melting points of an unknown substance and a pure substance, and the comparison of physical characteristics.
Extraction is a chemical method of separating a specific component of a solution from the rest of the solution. This is done by using a solvent in which the substance to be isolated is very soluble, while the rest of the solution is not as soluble.
Tea leaves consist mostly of cellulose, a water‐insoluble polymer of glucose, which is a monosaccharide. Cellulose performs a function in plants similar to that of fibrous proteins in animals: it is structure building material. Along with the cellulose are found a number of other things including caffeine, tannins (phenolic compounds, compounds that have an ‐OH directly bonded to an aromatic ring) and a small amount of chlorophyll.
The group was tasked to take 5 bags of commercially sold tea (caffeinated) and to boil for 5 minutes in water to extract the water soluble materials in the tea leaves into hot water which in this case would be caffeine. Using a separatory funnel, the organic layer was isolated and then evaporated to get crude caffeine. Crude caffeine was purified by recuptallization and then tested for purity with the melting point as a criterion.
Through the experiment, the group should be able to accomplish the following: (1) Isolate and purify caffeine from tea leaves, (2) characterize the purity of the isolated caffeine through a comparison of melting points with standard caffeine and (3) determine the percentage yield of caffeine in the tea leaves.
5 bags of tea are opened and weighed using the analytical balance. The leaves are then returned to the bags and boiled for 5 minutes in 100 mL of distilled water in a 250 mL beaker with a cover (a watch glass may do). After boiling it is then cooled in running tap water and an ice cube is added to the boiled solution to cool it down. The solution is then transferred to a separatory funnel then 20 mL of dichloromethane is added. The funnel is gently shaken several times and is opened once in a while to release pressure. The organic layer of CH2Cl2 being more dense than water is the lower layer. It is collected in a clean and dry Erlenmeyer flask. 20 mL of CH2Cl2 is added again and the process is repeated until 60 mL of CH2Cl2 has been added and the 3rd organic layer is taken and combined in the Erlenmeyer flask.
The combined organic layer in the Erlenmeyer flask is again transferred to in a separatory funnel and washed with 20 mL of 6M NaOH. The funnel is shaken vigorously until the 2 layers are clearly separated. The upper layer (NaOH) is discarded and the lower layer (organic layer) is collected in a 100 mL beaker. The solution is dried with 1-2 spatulas of anhydrous Na2SO4 to remove excess water. It is then filtered through a funnel with cotton and collected in an evaporating dish...