The extraction of caffeine (C8H10N402) was done in two parts. The first procedure used was solid-liquid extraction which was done by boiling the tea leaves in 100 ml. distilled water for 5-10 minutes. The filtrate was acquired and was extracted again by liquid-liquid extraction using dichloromethane (CH2Cl2). The combined DCM (CH2Cl2) was washed and dried to yield crude caffeine. The crude caffeine was purified by sublimation and the percentage yield was calculated by solving the ratio of the weight of the pure caffeine and weight of the tea leaves used. The computed percentage of caffeine was 0.12%. The temperature range of the pure caffeine was 215-220 °C.
Caffeine is an alkoid that belongs to the methylxanthine family. It is naturally produced by over 60 plant species. One of the products that contain caffeine is tea leaves. Aside from caffeine tea leaves also contain other organic compounds namely tannins, cellulose and flavonoids. Extraction is the process of obtaining something from a mixture or compound using chemical, physical, or mechanical means. The theory of extraction lies in the concept of immiscibility between two phases to separate a solute from the other phase. There are two types of extraction: solid-liquid and liquid-liquid. These two types of extraction were used in the experiment to obtain the following objectives: to isolate caffeine from tea leaves, to purify the isolated caffeine, to characterize caffeine and to compute the percentage yield of caffeine in tea leaves.
The first step that was done was the extraction of crude caffeine from 3 bags of tea leaves. The brand of the tea bags used was Lipton Yellow Label Tea. The tea leaves were taken first from the tea bags to measure the weight of the tea leaves. The lid of the tea bags were cut to obtain the tea leaves. The tea leaves were weighed using the use of analytical balance. The leaves were returned inside the tea bags and were boiled in 100 ml. water contained in a 250 ml. beaker for 5 minutes. The tea extract was not filtered because the tea bags didn’t burst. The tea extract was obtained and was transferred in a flask. The side of the flask was cooled off for 2 minutes with running tap water to decrease the temperature of the tea extract. After cooling down, the tea extract was transferred in a separatory funnel. The separatory funnel contained 20 mL of dichloromethane (CH2Cl2) and the tea extract. The separatory containing the H2O layer (tea extract) and DCM (CH2Cl2) was shook and turned upside down (Fig.1.1) until the separation of the layers were clearly visible and the pressure was released constantly by opening the stopcock.
Fig. 1.1 (Extraction using separatory funnel)
The lower layer which contains the DCM layer was drained in a clean flask. The extraction was repeated two more times and the lower layers were combined in a single clean flask. The upper layer was discarded. The DCM layer was returned in the separatory funnel and NaOH was added to wash the DCM layer. The lower layer was drained in a 250 ml. beaker and the upper layer was discarded. Half spatula of anhydrous Na2SO4 was added in the beaker containing the DCM layer and was stirred. The anhydrous Na2SO4 was settled in the beaker and the beaker was covered with a piece of paper with holes for evaporation of DCM. The crude caffeine was obtained after two days of evaporation. The second procedure was the purification of the crude caffeine. The crude caffeine was transferred in a filter tube with fitted inner test tube that contains cold water and served as the cold finger. The filter tube was placed inside a tin can with opened upper part and punctured lower part (Fig.1.2). The top part of the set-up was covered with aluminium foil. The whole set-up had undergone hot air bath using a Bunsen burner for 15 minutes. The cold water inside the...