Date Sent 2nd April 2012 th
Date Performed 26 March 2012
Isolation of Caffeine From a Tea Bag Experiment 1 By : Muhd Ridhuan Shahriman b Mohd Radzi For : Ms Zurhana bt Mat Hussin
CHM 556
Experiment 1: Isolation of Caffeine from a Tea Bag
Objective: In this experiment, caffeine is isolated from a tea solution. Caffeine is an analgesic drug that increases the heart rate. It exists naturally in especially tea and coffee. Caffeine constitutes as much as 5% by weight of the leaf material in tea bags.
Molecular structure of caffeine
Introduction: Extraction process selectively dissolves one or more of the mixture compounds into a suitable solvent. The solution of these dissolved compounds is referred to as the extract. Here the organic solvent methylene chloride is used to extract caffeine from an aqueous extract of tea leaves because caffeine is more soluble in methylene chloride than it is in water.
Caffeine is also known as 1,3,7 – trimethylxanthine. Caffeine constitutes as much as 5% of the weight weigh t of the leaf material in tea plant. Tea leaf, like any other leaves are made up mostly of cellulose and chlorophylls. Oxidized flavenoid pigments and chlorophylls basically give the brown color of the tea. In this experiment, we will be extracting pure caffeine from a tea bag using methylene chloride. Although chlorophylls are soluble in methylene chloride, most other substances in tea are not. Thus, the methylene chloride extraction of the basic tea solution removes nearly pure caffeine. The methylene chloride is easily removed by evaporation (b.p of methylene chloride is 40°C) to leave the crude caffeine. The caffeine can then be purified by sublimation.
Material: 1. 2. 3. 4. 5. 6.
100 mL beaker 250 mL conical flask flask Cotton for filtration Separatory funnel Bunsen burner 50 mL round-bottomed flask
Chemical: 1. 2. 3. 4. 5.
Tea bag Methylene chloride Distilled water Anhydrous sodium sulphate, NaSO 4 Sodium carbonate, Na 2CO3
Procedure: 1. Preparing the Tea Solution a. 50 mL water inside a 100 mL beaker was heated under gentle reflux until it reaches boiling point. b. A tea bag was then placed inside the beaker. The tea bag is ensured to lie flat on the bottom of the beaker. 2. Extraction a. The hot tea solution was transferred into a small conical flask. b. Then, 0.5 g of sodium carbonate, Na 2CO3 was added into it. c. The mixture was shaken gently to dissolve the salt. d. The mixture was filtered into a small separating funnel by using cotton. e. 15 mL of methylene chloride was later transferred into the separating funnel, which immediately forms a second layer. f. After gently shaking it, the lower layer of the mixture is drained off and was added 10 mL of fresh methylene chloride. g. The re-addition of methylene chloride was repeated twice to ensure maximum extraction of caffeine. h. The combined methylene chloride layer was later dried by using anhydrous sodium sulphate. i. The dried methylene chloride solution was then transferred into a pre-weighed small round-bottomed flask and was evaporated using the rotary-evaporator.
Results :
Mass of sodium carbonate: 0.51 g Mass of tea (minus the bag): 2.41 g Mass of caffeine obtained: 0.05g Melting point of caffeine: 209.8 °C Actual melting point of caffeine: 229 °C
Observation:
After the tea solution has been added sodium carbonate, it was later mixed with methylene chloride in the ratio 10mL tea: 3mL methylene chloride. Some changes were made, while separating the mixture, separatory funnel is replaced with centrifuging machine. The tea solution was separated into 3 test tubes containing two 10mL and one 6.5mL of tea solution. Those 3 test tubes are filled with methylene chloride in the ratio of 10mL tea : 3mL methylene chloride. Then, the tubes were centrifuged for 1 minute at 2250 rpm. Then, the clear methylene chloride layer on the tubes were extracted and combined in a 25mL beaker. The extracted methylene chloride was added 5.1g of anhydrous sodium sulphate to dry the water off. The extract was evaporated using the rotary evaporator.
Calculations: Mass of caffeine obtained: 0.05g Percentage of caffeine: :
:
: 2.01 %
Discussions The purpose of this experiment was to extract caffeine, an analgesic drug naturally formed from tea leaves. The caffeine in the tea is separated by using methylene chloride. In this experiment, mass of caffeine obtained was 0.05g and the melting point is recorded at 209 °C. As stated earlier, caffeine constitutes almost 5% of the mass of the tea leaf. The percentage of caffeine in this experiment is 2.01%. The reason why the percentage
is not at 5% is because the extraction process could have been more efficient. Some of the caffeine might have been still in the tea bag or in the cotton filter. The melting point p oint of caffeine (2.09°C) in this t his experiment diverts d iverts from the actual one (229°C). This error can be traced back in the purification of caffeine where it is suspected that traces of methylene chloride could still be mixed with caffeine. The traces of methylene chloride could lower the melting point of caffeine. The reason why we use methylene chloride in this experiment is because it is denser than water, which is good because it will make it easier to extract. Caffeine is also more soluble in methylene chloride than it is in water. In addition, a lot of other substance is also soluble in water but not in methylene chloride, which is later is more difficult as we need to purify the caffeine.
CONCLUSIONS Caffeine was successfully extracted from a bag of o f tea leaves. The caffeine percentage in the tea solution is 2.01%. The mass of caffeine extracted was 0.05g. 0.05 g. The melting point of caffeine is i s 209°. 209°.
REFERENCES 1. “Introduction
to Organic Laboratory Techniques ” 2011 Brooks/Cole Publication Randall G. Engel Page 498
2. “Organic Chemistry”
2011 Wiley Publication T.W. Graham Solomon Page 729
