Isolation of caffeine from tea leave

Date of experiment: September 3rd, 2013
Organic Chemistry II – CHLB330
Name: Symone MoxeyLab Partner: Lynden Cooper
Isolation of caffeine from tea leave
Abstract:-
Introduction:-
Caffeine is probably the most commonly used addictive drug. This drug is found in a number of things ingested by people. It belongs to a group of nitrogen bases called purines. Because caffeine possesses these base-like properties, it is described as an alkaloid. They usually taste bitter and often are physiologically active in humans. The structure of caffeine is shown below. Figure 1: Structure of Caffeine
In this experiment, you are going to make a small but strong cup of tea and extract the caffeine from it. Also, you are going to purify the caffeine by recrystallization and calculate the mass percentage of caffeine in the tea sample using the equation below.
Mass % = (wt. of purified caffeine / wt. of tea sample) x 100
Caffeine is a very common substance and is found in coffee, tea, soft drinks, chocolate, and "stay-awake" pills such as Vivarin. In Humans, Caffeine acts to stimulate the heart, central nervous system, and the respiratory system. Blood pressure is increased by its use, since heart rate is increased, as is contraction force and volume output. It is a diuretic and has the effect of delaying fatigue. Caffeine has a bitter taste.
The isolation of Caffeine from tea is a simple-seeming experiment, which in fact makes use of a number of rather advanced chemical processes. To isolate the Caffeine in a sample of tea, it is necessary to chemically separate the Caffeine from the rest of the tea prior to evaporation. This process is known as an extraction. An 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 this case Chloroform) in which the substance to be isolated is very soluble, while the rest of the solution is not as soluble. For the purposes of this experiment, Chloroform was chosen as the solvent because Caffeine is very soluble in this substance. Thus, when the separatory funnel is used, the Caffeine in the tea dissolves into the Chloroform and the rest of the tea can be discarded. This is done three times so that the amount of Caffeine left in the discarded tea is minimized. The caffeine dissolves in the chloroform whereas the sales of the tannins remain in the aqueous solution. Evaporation of the methylene chloride yields crude caffeine which is then purified by recrystallization.
Equations:-
DATA TABLE 1
Original Mass of tea bags 34.9g
Weight of empty Erlenmeyer flask 76.7g
Weight of (Flask +crude caffeine) 76.9g
Mass of Valve and Pure Caffeine 8.71g
Mass of Pure Caffeine 0.14g
Melting Point of Caffeine 225°C-227°C
Table of Reagents:-
Substance M.W/ gmol-1 Density g/cm3 Solubility M.P / °C B.P/°C
Caffeine 194.1926 1.23 Soluble 236-238 175-176
Sodium Carbonate (anhydrous) 105.98874 2.54 Soluble 851 1600
Methylene chloride 84.9328 1.48 (Miscible with most organic liquids) Soluble -63.5 61.2
Acetone 88.106 0.792 Highly soluble -95.4 56.2
Petroleum Ether 0.77 at 20°C Insoluble in cold water -95 60
Experimental:-
This experiment is done according to the procedure found on pages 4 and 5 of the Organic Chemistry II (Chemistry 330) Practical Handbook.
Results:-
As the bags began to boil over a period of eleven (11) minutes the water turned dark brown in colour. After boiling, an aroma similar to bush medicine is detected

Discussion:-
The melting point of the pure caffeine that was obtained from the experiment was lower than the literature value (236°C). There are some explanations as to why the melting point would be lower. One reason is, the purification process was not perfect, and there were impurities in the caffeine affecting the melting point. The melting point depresses due to impurities in the sample. The results obtained were expected since, it is known that tea is not 100% caffeine and the caffeine would not be 100% pure in the end. The percent recovery of the pure caffeine was not going to 100% since caffeine constitutes as much as 5% by weight of the leaf material in plants.