Caffeine is a stimulant alkaloid with a cyclic backbone structure that corresponds to the purine structures of DNA, giving it the ability to affect the body's biochemical pathways.1🇧🇷 In commercial applications, caffeine supplements medicines and certain beverages such as coffee or tea. Standard tea bags contain 2.00 +/- 0.05g of tea leaves along with around 55mg of caffeine🇧🇷 With the right extraction methods, the caffeine in a tea bag could be isolated to produce a pure solid; the mass of this solid would reflect the actual caffeine content in the tea. To do this, caffeine must be placed in a volatile and water-insoluble solvent; a perfect example is methylene chloride🇧🇷 Caffeine has a greater affinity for methylene chloride and easily dissolves in water in this solvent; However, caffeine is not the only organic substance in tea that can react with methylene chloride. In addition to caffeine, tea bags contain organic substances called tannins or gallic acid.1🇧🇷 Both caffeine and gallic acid can dissolve in water; However, caffeine has a greater attraction to water due to the dipole-dipole interaction that results from caffeine's increased polarity and the hydrogen bonds that form between caffeine and water.1🇧🇷 In theory, the intermolecular forces of gallic acid can be manipulated to induce a stronger dipole-ion interaction. If a common salt like sodium carbonate were introduced into the solution, the gallic acid could be converted back to the phenolic salt: a polar inorganic molecule insoluble in methylene chloride..
In methylene chloride, caffeine will have a greater attraction for the organic solvent and the hydrogen bonds between caffeine and water will be broken. Using a separation apparatus, two insoluble solutions can be separated, isolating the caffeine and the new phenolic anion from each other. The denser methylene chloride layer can be removed from the funnel to obtain a pure methylene chloride-caffeine solution. To ensure that water does not interfere with the caffeine's interaction with methylene chloride, sodium sulfate can be used to absorb excess water that has escaped from the tea solution.1🇧🇷 When heated, the solvent would quickly evaporate due to the low boiling point of methylene chloride.2🇧🇷 The remaining solid would then be pure caffeine.
First, a 150 mL beaker was prepared with 50 mL of deionized water and 2 boiling stones to dissolve 2.0 g of sodium carbonate and react with the gallic acid in the tea. The beaker was heated until the water boiled, at which point the temperature was lowered and 2 tea bags were added to the water. The solution was heated for 10 to 12 minutes to achieve the highest tea concentration. At the same time, the insoluble components of the tea cellulose were separated from the solution, resulting in tea concentrate, caffeine and the new phenolic anion product. The final saturated solution was poured into a 100 mL beaker while the liquids trapped in the tea bags were simultaneously rinsed with another 10 mL of deionized water. After cooling, the solution was transferred to a 125 mL separator, a glass funnel used to separate immiscible solutions. From the top of the funnel, methylene chloride was poured into the solution in 5 mL increments. After each addition of methylene chloride, the funnel was inverted to release the pressure built up by the reaction. The reaction produced a tea brown upper layer and a light lower layer of dense methylene chloride. The lower layer was removed from the stopcock and collected in a 100 mL beaker, leaving a thin layer of methylene chloride to prevent contamination.
Methylene chloride was added twice more to ensure it had reacted with all of the caffeine. Sodium sulfate was added to the extract to absorb the water escaping from the tea and the remaining liquid was decanted and rinsed into a 50 mL beaker preweighed with boiling stones using an additional 2.0 mL of methylene chloride. Upon boiling, the volatile methylene chloride evaporated and turned into pure, solid caffeine.,,
Figure 3: Graph of the IR spectrum of caffeine
Standard measures provided by Lipton Tea manufacturers are accepted as experimental measures for tea and caffeine. The approximate weight of a single Lipton tea bag is 2.00 ± 0.05g and contains 55mg of caffeine per bag. For a trial with 2 teabags, 110mg is the expected caffeine yield. During the extraction process, a 50 ml beaker was weighed together with 2 boiling stones with a total mass of 27.56 g. To extract the caffeine, the heated tea solution was poured into an insulated separatory funnel along with 5 mL of methylene chloride and inverted to mix the solution well. Due to the reaction, pressure builds up inside the funnel, forcing the stopcock to open to release excess gas after each inversion. After settling, the solution separated into 2 layers: the polar brown tea solution at the top and the clear non-polar methylene chloride solution at the bottom. Tea was deposited over methylene chloride because the density of water is 0.997 g/ml but the density of methylene chloride is 1.32 g/ml. Between the two layers were small bubbles or possible emulsions that limited the amount of methylene chloride that could be extracted. Nonetheless, the methylene chloride/caffeine layer was efficiently drained into the previously weighed 50 mL beaker and the process repeated 2 more times to ensure that all of the caffeine had reacted. As the ambient temperature increased, volatile methylene chloride began to evaporate into the environment. The remaining solution was briefly heated until the volatile solvent had evaporated and the solid caffeine remained. When weighed, the mug, stones, and caffeine totaled 27.58 g. The mass difference between the initial beaker weight and the final product was then the actual caffeine yield, 0.02 g. Compared to the theoretical mass, the experiment gave a caffeine yield of 18.18%.
The solid caffeine product was run through an infrared spectrometer, which uses binding energies to identify chemical compounds. The spectrometer generated a graph based on photon energy measurements in a frequency range between 400 and 4000 Hz. Individual peaks in the graph indicate the unique binding energies of specific functional groups. For example, the visible photon energy peak around the 3000 Hz frequency represents the apparent amine and amide group in caffeine. The other main peak appears around 1600 Hz and 1750 Hz. This peak represents the alkene portion of the caffeine molecule. Using these individual peaks of photon energy, the infrared spectrometer predicts the composition of the compound present. The spectrometer predicted there was an 869 in 1,000 chance that the sample produced was caffeine. This value is not related to the purity of the caffeine.
As expected, the percent caffeine yield was not 100%; however, achieving this goal is impossible. The caffeine mass of 2 Lipton teabags was only 18.18% of the theoretical yield, but considering all the factors responsible for the error, 18.18% is an acceptable value. The performance error results from a series of unavoidable experimental errors. The first defect is caused by the reaction between gallic acid and sodium carbonate. Although the conversion of gallic acid is necessary for the reaction of caffeine and methylene chloride to occur, the phenolic anion by-product of this reaction is responsible for the necessary error.🇧🇷 Anionic surfactants are formed when phenolic acids are converted back into salts.4🇧🇷 These surfactants are responsible for emulsifying water-insoluble materials such as methylene chloride. As a result, both polar and non-polar solutions create large soap bubbles called emulsions. During the extraction phase of this experiment, these bubbles limited the amount of caffeine released from the separatory funnel, resulting in a lower yield. Another source of inferior performance came from techniques used to avoid contamination of the methylene chloride solution. While the caffeine was being extracted it was necessary to leave a small layer of methylene chloride behind to avoid contamination of the final product.🇧🇷 Discarding some of the methylene chloride solution left some of the caffeine behind and impacted the overall performance of the product. The final source of error is unavoidable environmental conditions. As a result of the hotplates used prior to the caffeine extraction phase, the laboratory temperature was increased. Methylene chloride does not normally vaporize at room temperature, but outdoors at a higher temperature the solution reacted earlier, causing less methylene chloride to react with the caffeine. This would result in less caffeine being withdrawn from the solution and performance dropping.
- Study the structure of caffeine and determine the strongest intermolecular force that exists.
The strongest intermolecular force in caffeine is the dipole-dipole interaction due to the polarity of the molecule. The molecule's dipole moment overcomes the weak van der Waals forces, making it the strongest intermolecular force in caffeine.
2. Why is caffeine more soluble in methylene chloride than in water?
Caffeine is more soluble in methylene chloride than water because both caffeine and methylene chloride are organic substances while water is inorganic. Although caffeine is able to dissolve in water to form hydrogen bonds, the greater affinity that caffeine has for methylene chloride breaks these bonds.
3.Describe the purpose of adding sodium carbonate to the reaction mixture.
The purpose of adding sodium carbonate to the mixture was to change the chemical structure of gallic acid. Initially, gallic acid has a slight affinity for methylene chloride, which would oppose the reaction between caffeine and methylene solvent. By introducing a saturated basic sodium carbonate into the solution, the gallic acid is converted into an inorganic phenolic salt which is insoluble in methylene chloride but highly soluble in water. As a result, methylene chloride extract contains the highest yield of caffeine alone.
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