Isolation Of Caffeine From Tea Experiment 5 Lab Report

Experiment 5: Isolation of Caffeine from Tea Purpose: The purpose of this experiment was to isolate and purify caffeine from tea. There were two parts to this experiment. The purpose of the first part was to utilize extraction to isolate the caffeine from a tea bag. The purpose of the second part was to use sublimation to purify the isolated crude caffeine sample. Procedure: In the first part of the experiment, a tea bag and 30 mL of deionized water were placed in a 100 mL beaker. The beaker was placed on a hot place and was heated until only 8-10 mL of liquid remained in the beaker. The concentrated tea solution was transferred to a screw cap conical tube. 100mg of calcium carbonate was added to the tube and shaken for 5 minutes. The solution was allowed to cool to room temperature and was filtered using a Büchner funnel. The aqueous solution was transferred to a separatory flask and was extracted two times with 3 mL portions of dichloromethane. The organic layer was collected in a small test tube and was dried with sodium sulfate. The solution was transferred to a tared 10 mL round bottom flask leaving the drying agent behind. The solvent was evaporated using a rotary evaporator and the yield and appearance of the crude sample was determined. In the second part of the experiment, the crude samples of caffeine of six different lab members were dissolved in dichloromethane and combined in a side arm test tube. Prior to dissolving the crude sample in dichloromethane, the melting point of the crude sample from only one lab member was observed. The dichloromethane was then evaporated by placing the side arm test tube in a beaker of water and placing the beaker on a hot plate until all the liquid was gone. The yields of the crude sample from each lab member were added together to calculate a theoretical yield for the pure sample. A sublimation apparatus was assembled and the sample was sublimed. The pure caffeine sample was scraped from the apparatus into a tared watch glass and the yield, melting point, and appearance of the pure sample were determined. Calculations: 1) Percent Recovery of Crude Caffeine Sample Observed Yield ∗100 % Amount of Caffeine found∈Typical Tea Bag 0.010 g ∗100 %=28.6 % Percent Recovery = 0.035 g P ercent Recovery= 2) Theoretical Yield of Pure Caffeine Sample Theoretical Yield=∑ of Crude Yield ¿ Each of Six Lab Me mbers Theoretical Yield=0.01 g+ 0.01 g+0.02 g+0.02 g+ 0.03 g+0.03 g=0.11 g 3) Percent Recovery of Pure Caffeine Sample Observed Yield ∗100 % Theoretical Yield 0.02 g ∗100 %=18.2 % Percen t Recovery= 0.11g Percent Recovery = Results: *Table 1 shows that the percent recovery for both the crude and pure caffeine samples was rather low. The reason for a low percent recovery for the crude sample was likely experimental errors such as spillage. The low percent recovery for the pure sample was most likely due to impurities in the crude samples the pure sample was sublimed from. The melting points of both the crude and pure caffeine samples were both close to the actual melting point of caffeine which is 234-239°C; however the crude sample exhibited a wider melting point range than the pure sample. The pure sample was much closer to white in its appearance than the crude sample, visually confirming the difference in purity between the two samples. Discussion: The purpose of the first part of the experiment was to isolate caffeine from a tea bag using extraction. Extraction is the process of transferring a solute from one solvent to another and is useful for isolating and purifying the different compounds in a solution. The two solvents used are not miscible and form two separate layers. The solute moves from the solvent in which is it less soluble to the solvent in which it is more soluble; the solute is extracted from one solute to the second solvent. In this experiment, caffeine was extracted from the aqueous, polar solvent to the organic, non-polar layer through deprotonation (Appendix A). The observed yield of the crude caffeine was much lower than the expected yield of about 35mg. The percent recovery of crude caffeine was only 28.6% indicating that a significant amount caffeine was lost during the experiment. Extraction is not usually a wasteful process indicating that this loss was mainly caused by experimental errors such as spillage. The melting point of the crude sample observed was lower than the expected 234-239°C melting point by 3°C for both the starting and ending points of the observed melting range which was 231-236°C. This is typical of an impure substance because contaminants cause the melting point of a crude substance to be lower than the expected melting point of a pure sample of the same substance. This is because the contaminants prevent the sample from forming the crystal lattices that are in the pure substance. The crystal lattices create strong bonds, making the substance harder to melt. Without these bonds, the bonds of the impure substance are easier to break, thus making the substance easier to melt. While calcium carbonate was effective in removing tannin/catechin derivatives (Appendix B), other contaminants were present in the crude samples. Both cellulose and chlorophyll are water insoluble, meaning that both of these compounds were extracted into the aqueous layer and remained in the organic layer that was collected for the crude caffeine sample. This contamination is confirmed by the yellow color of the crude sample, caused by chlorophyll, as opposed to the color of the pure sample which was almost white. However, the observed melting point range overlapped with the expected melting point range at 234236°C indicating that the crude sample that was melted was relatively pure with minimal contaminants. The purpose of the second part of the experiment was to purify caffeine using sublimation. Sublimation is a process used when the substance to be purified has the ability to transform from its solid state to its vapor state and/or condense from its vapor state to its solid state without passing through a liquid phase. It is also necessary that the contaminants in the crude sample will not sublime under the same conditions that the substance to purified sublimes. In this experiment, caffeine sublimes under different conditions than the chlorophyll contaminants in the crude sample. The observed yield of pure caffeine was much lower than the amount of crude caffeine used for sublimation. It is expected that the yield of pure caffeine would not be very high due to the aforementioned contaminants. However, the results from the first part of the experiment showed that the crude sample was relatively pure. A higher percent recovery would have been expected, indicating that sublimation was wasteful of the sample. The appearance of the pure sample was similar to the expected appearance of a pure caffeine sample. The sample had an off-white color rather than the expected pure white, indicating that there were still some contaminants in the sample. However there were much fewer contaminants in the pure sample than in the crude sample as the pure sample was much closer to the expected white color than the crude sample. Sublimation was effective in purifying the sample; however, the off-white color suggests that more purification needed to be performed. This conclusion is supported by the observed melting point of 234-236°C. The observed melting point had the same starting point as the expected melting point (234°C) but the observed end point was lower than the theoretical end point of 239°C. This shows that contaminants were still present in the sample causing a lower melting point. Error Analysis: The main cause of the low percent recovery in the crude caffeine sample from the first part of the experiment was experimental errors. The biggest error that occurred was spillage during extraction. During extraction when the separatory flask was inverted to mix the layers, the plug used at the opening of the flask was too small and liquid spilled out causing a loss of volume in both the organic and aqueous layers. This error was quickly corrected by replacing the plug with one of appropriate size; however, some potential caffeine yield was lost. In the future, special care should be taken to ensure that a plug of correct size is used in order to prevent this spillage. Caffeine dissolves in water because it is a positively charged molecule, making it soluble in polar water. In the future, more water can be used to boil the tea so that a maximum amount of caffeine can be dissolved. The tea will remain in the water for a longer amount of time, ensuring that more caffeine will dissolve. Other measures can also be taken to increase caffeine yield. Special care should be taken to squeeze all of the liquid out of the tea bag when collecting the concentrated tea solution. The tea bag was only washed with hot deionized water once and in the future, this washing can be performed multiple times in order to obtain as much caffeine as possible. The poor yield of pure caffeine from the crude caffeine sample shows that sublimation was not a good method of purification for caffeine in this experiment. Product loss could have occurred during the sublimation process if the caffeine did not condense back to its solid form and instead escaped from the apparatus as a vapor. Product loss also could have occurred when transferring the sample from the sublimation apparatus to the tared watch glass. Another method of purification that could be used in the future instead of sublimation is crystallization. Crystallization is a selective process that is effective in purifying a substance, especially if it is performed multiple times on the same sample. Crystallization also provides for minimization of product loss. Another source of error in this experiment was the combination of samples of different lab members. The samples potentially varied in purity; some samples may have been more pure than others. The melting point of only one crude sample was taken; however, this melting point could have been a misrepresentation of the purity of the combined sample. The observed melting could have been more or less pure than the combined sample as a whole. In the future, a small sample can be obtained from the side arm test tube after all of the methylene chloride has been evaporated and the melting point of the combined sample can be observed to obtain a more representative melting point. Lastly, when observing the melting point of both the crude and pure samples of caffeine, only one melting point apparatus was used, meaning that only one lab member could look at the samples at a time. There was disagreement among lab members on when the samples began melting and when the samples were completely melted. Melting ranges were eventually agreed upon but there is a great insecurity in these numbers because of the differences in opinion. There are two potential changes that can be made in the future to remedy this problem. Crude samples were combined because of the inefficiency of sublimation as a purification process. In the future, the experiment could be performed on the macroscale rather than the microscale so that the amount of crude sample obtained would be sufficient in providing enough material for a melting point observation and for a pure sample to be obtained from sublimation. Another option is that a different purification process that requires less crude material could be utilized. Thus, each lab member will have a melting point for both the crude and pure caffeine from personal samples eliminating any disagreement. Conclusion: Extraction and sublimation are two laboratory methods utilized for isolating and purifying different substances. Specifically in this experiment, extraction was used to isolate caffeine from tea and sublimation was used to purify the crude caffeine sample obtained from the extraction. In the extraction portion of the experiment, it was shown that experimental errors caused a low percent recovery of the crude caffeine. However, these experimental errors can be easily improved in future experiments by increased attentiveness. The crude caffeine obtained was contaminated by chlorophyll as observed visually by the yellow appearance of the sample and observed experimentally by a lowered melting point. The melting point observed indicated that the crude sample had few impurities because it overlapped with the theoretical melting point range of pure caffeine. In the sublimation portion of the experiment, there was a very low percent recovery indicating that sublimation was not an efficient method of purification for this experiment. Different methods of purification, such as crystallization, can be utilized in the future in an attempt to increase the percent recovery of pure caffeine while still effectively purify the sample. The melting point of the pure sample was closer to the theoretical melting point than the melting point of the pure sample showing that sublimation was effective in purifying caffeine from the crude sample. This was also confirmed visually as the pure sample appeared closer to the ideal white color of pure caffeine than the crude sample. Appendix A: Extraction of Caffeine into the Organic Layer Using Calcium Carbonate ** (University of Virginia, pp.53) **Calcium carbonate deprotonates caffeine making it an uncharged molecule. This allows for caffeine to move from the charged, aqueous layer to the uncharged, organic layer. Appendix B: Removal of Tannins/Catechin Derivatives from Organic Layer Using Calcium Carbonate ***