CHEM 230L _Extraction of Caffeine from Tea Leaves

pdf

School

Chapman University *

*We aren’t endorsed by this school

Course

230L

Subject

Chemistry

Date

Jan 9, 2024

Type

pdf

Pages

Uploaded by ProfMorningMouse32

CHEM 230L: Organic Chemistry I Lab Chapman University Experiment 4: Extraction and Purification of Caffeine from Tea Leaves Intended Learning Outcomes By completing this lab, we will: • Understand how the solubility of solutes in different immiscible solvents can be used in extraction of solutes form complex liquid solutions. • Learn how to extract organic compounds from an aqueous solution. • Learn how to purify solids by using sublimation. Introduction Caffeine is a naturally occurring alkaloid that acts as a stimulant of the central nervous system by binding to and therefore blocking Adenosine receptors in the brain. Two of the most common sources of caffeine are tea leaves and coffee beans. However, extraction of any specific naturally occurring molecule from its natural source can be difficult because the desirable molecule will be a part of a complex mixture. Because of this, extraction and purification are often paired together to isolate a single or small group of compounds. Once the molecule is extracted along with some impurities, a purification technique can be used to obtain only the desired molecule. In this experiment you will extract caffeine from tea leaves and use sublimation to purify the caffeine. Caffeine and several other compounds will be extracted from an aqueous solution (concentrated black tea) using an extraction solvent that is immiscible with water. In this case, dichloromethane (methylene chloride) will be used as the extracting solvent. In such a liquid- liquid extraction, the compounds in the initial crude solution will have differing solubilities in the solvent of crude solution and that being used for extraction (extracting solvent). Ideally, the desired compound(s) that is extracted will have a significantly higher solubility in the extracting solvent that the solvent being extracted from. In addition, it is desired that undesired compounds have a higher solubility in the crude mixture solvent than the extracting solvent so that they are left behind. For this specific case, caffeine has a much higher solubility in dichloromethane than it does water and most of the other compounds in the tea have a higher solubility in water than they do in dichloromethane. Pre-Lab Reading The reading below needs to be completed before the start of lab. 1. Lab textbook (Pavia, 6 th edition): Technique 12 – Extractions, Separations, and Drying Agents (part A-E): pages 718-738. Lab textbook (Pavia, 6 th edition): Technique 17 – Sublimation: pages 797-801. 2. Carefully read the procedure for the lab experiment below to ensure that you generally understand the purpose of each step.

CHEM 230L: Organic Chemistry I Lab Chapman University Pre-Lab Assignment (15 points) Answer the following questions: 1. Water and diethyl ether are immiscible and will form two layers when added to a separatory funnel. which solvent will be the top layer? What physical property could you look up to determine this? What could you do in the lab to determine this instead of looking up the physical property. (4 pts.) Density: Water – 1 g/mL Diethyl Ether – 0.706 g/mL Diethyl Ether will be the top layer since it is less dense than water. The physical property used is its density. In lab, we can put two immiscible liquids together in a container, and whichever one is the top layer will be the less dense solvent, and whichever one is the bottom layer will be the more dense solvent. To get a rough measure of the solvent’s literature density, we can also weigh a certain amount (mL) of solvent in grams, and then divide the grams by the milliliters to get a value for its density. 2. When extracting compounds from aqueous solutions using dichloromethane, there will always be trace amount of water in the dichloromethane even if a clean separation occurs. How can these trace amounts of water be removed from the dichloromethane? (2 pts.) A drying agent can be used to “dry out” the trace amount of water left. An anhydrous inorganic salt can be placed into the solution in which it soaks up the leftover water molecules. Common ones used are sodium sulfate, magnesium sulfate, calcium chloride, and calcium sulfate. 3. What about sublimation is unique compared to other physical state transitions such as vaporization? Why is low pressure used in the sublimation process? If a vacuum system is not strong enough to generate low pressure, does the temperature required for a compound to sublime increase or decrease? (4 pts.) Sublimation is unique compared to other physical state transitions such as vaporization because certain molecules that can sublime are able to convert between solid and gas states without turning into a liquid prior to the gas phase. Low pressure is used in the sublimation process because it enables solids to sublime at lower temperatures just as how liquids tend to boil quicker at lower pressures. If a vacuum fails to generate low pressure, the temperature for a compound to sublime will increase as there will be more pressure to push through in the surrounding environment/container. 4. A student recovers 175 mg of caffeine from a large bag of tea that had a total mass of 2 grams. Calculate the % caffeine by mass for the bag of tea. Comment on why this low % caffeine most likely does not have to do with a poorly done extraction. (5 pts.) 175 mg / 1000 = 0.175 g caffeine 0.175 g / 2 g = 0.0875 * 100% = 8.75% caffeine This low % caffeine may not have to do with a poorly done extraction because some teas just have a lower caffeine content compared to other teas. Procedure

CHEM 230L: Organic Chemistry I Lab Chapman University A. Extraction of Caffeine: 1. Weigh two tea bags and record the mass. Place the tea in a 50- or 100-mL beaker and add 20 mL DI water to it. Mark the water level using a pen or tape on the beaker. 410 mg each x 2 = 820 mg 2. Heat the beaker on a hotplate until the water begins to boil and continue to allow the solution to boil for 15 minutes. During boiling, the level of the water will drop below the initial volume due to vaporization. Add water throughout the boiling process to keep the water level at this initial level. 3. After the solution has boiled for 15 minutes, remove the tea bags from the beaker and squeeze the absorbed tea solution out of them very thoroughly, but carefully (try not to rip the tea bags). 4. While still warm, add 0.5 g Na 2 CO 3 to the solution and stir until all or most of the solid Na 2 CO 3 dissolves. 5. Allow the solution to cool to room temperature and then transfer the contents to a separatory funnel. Make sure the stopcock for the separatory funnel is closed or you will lose tea out of the spot. is closed. 6. Add 10 mL of dichloromethane to the separatory funnel and cap the separatory funnel. Invert and shake the separatory funnel to mix the contents. Do this several times, opening the stopcock to vent pressure build up periodically. 7. Secure the separatory funnel with a clamp in the fume hood and wait until the aqueous and dichloromethane layers are cleanly separated. Open the stopcock and transfer the dichloromethane into a 50 mL Erlenmeyer flask. 8. Repeat steps 6 and 7 with another 10 mL of dichloromethane and transfer this second portion into the same flask as the first. Keep your aqueous layer in the separatory funnel and keep until the end of the lab. 9. Dry the dichloromethane solution with a minimum amount of anhydrous Na 2 SO 4 (ask your instructor how to do this properly – look for a clear solution and free moving Na 2 SO 4 particles). Cover the flask with a beaker to prevent dust getting into the flask and let the solution sit for a few minutes, allowing the Na 2 SO 4 to dry the solution. 10. Transfer the dried dichloromethane solution to the pre-weighed (record the mass) sublimation tube (10 mL conical tube) slowly by filling the sublimation tube about halfway and evaporating the dichloromethane by lightly blowing a stream of lab air on the dichloromethane. Repeat until all the dichloromethane solution has been transferred to

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

CHEM 230L: Organic Chemistry I Lab Chapman University the sublimation tube and evaporated to dryness. What remains should be a sticky solid or oil that appears white or light yellow in appearance. Weigh and record the mass of the conical vial with the crude caffeine. 11.997 g – sublimation tube B. Purification of Caffeine by Sublimation 1. Assemble the sublimation apparatus as shown in figure 17.2 (page 800) of the lab textbook and make sure the system does not have any leaks. Connect the vacuum tube to the system and open the vacuum line. 2. Add ice-cold water to the cool finger and use a copper wire to push all air bubbles out from the cool finger (this is very important) . 3. Use a Bunsen burner to heat up the bottom of the conical tube, moving the flame constantly to prevent the temperature from getting too high (which could cause the caffeine to decompose). 4. Pure white crystals of caffeine will condense onto the cold finger, keep heating the conical tube until the tube is dry and then turn off Bunsen burner and let the sublimation system cool to room temperature. 5. Close the vacuum line before disconnecting the vacuum tube from the sublimation apparatus. Carefully disconnect the vacuum line to avoid blowing the crystal on the cool finger down to the conical tube. 6. Scratch the caffeine crystals onto a tared piece of weighing paper to obtain and record the mass of Caffeine. Observe and record the physical appearance of the crystals 7. Take the melting point of the pure caffeine (literature melting point: 235 – 237 o C) using the MelTemp apparatus. 130 C Post-Lab Assignment (40 points) Data Analysis 1. Enter the mass of the two bags of tea used (1pt.) ___ 820 mg _______ 2. Enter the mass of the crude caffeine obtained by extraction (1pt.) ___ 1 mg _______ 3. Enter the mass of the extracted caffeine purified by sublimation (1pt.) ___ 1 mg _______

CHEM 230L: Organic Chemistry I Lab Chapman University 4. Determine the % recovery of purified caffeine from the entire mass of tea that was used. Show your calculation. (5 pts.) 1/820=0.00122 * 100% = .12% % Recovery _____ .12% _________ 5. Determine the % recovery of purified caffeine from just the caffeine in the tea if you assume that one tea bag contains 50 mg of caffeine. Show your calculation. (5 pts.) 1/100 = .01 * 100% = 1% % Recovery ____ 1%__________ 6. Describe the physical appearance of the purified caffeine crystals. (2 pts.) The purified caffeine crystals appear dusty and powdery. They seem to stick to surfaces and each other pretty well. 7. What was the melting point of the purified caffeine. (2 pts.) 130 C

CHEM 230L: Organic Chemistry I Lab Chapman University 8. Based off observed melting point and the literature value for the melting point of caffeine. Comment on if you were able to purity of your recovered caffeine and explain your reasoning (4 pts.) Since the melting point of my “purified” caffeine was 130 C, about 100-110 C lower than the literature value, I conclude that I was unable to purify my recovered caffeine. 9. Overall, comment on the effectiveness of the extraction and purification you performed. Were you able to extract a good amount based just off caffeine content (50 mg. per bag)? Did the sublimation work well? etc. (3 pts.) Given that I was only able to extract 1% of the supposed 100 mg total, I was unable to yield a good amount. While going through the experiment, every step seemed to go flawlessly. However, looking back at the experiment now knowing that my caffeine yield was so low, I recognize that there was leakage during the separatory funnel stage when I was flipping it back and forth, and there was more leakage when I was releasing the dichloromethane into the beaker. I may have used too much heat with the Bunsen burner as well, which could have vaporized some of the purified caffeine. Conceptual Questions: 1. What are two possible modifications that you could have made to the extraction procedure to increase the amount of caffeine recovered? Explain how these modifications would have increased the amount of caffeine recovered. (4 pts.) Ensure that the separatory funnel is sealed tight so no aqueous solution can leak out, and also slowing down the release process of the dichloromethane into the beaker. This would ensure that no caffeine is lost in the aggravation process between the tea and the dichloromethane, and it will also ensure that no tea leaks down into the resulting dichloromethane in the beaker. 3. When extracting caffeine from aqueous solution using dichloromethane, would it be better to use three 4 mL aliquots of dichloromethane or one 12 mL aliquot of dichloromethane? Explain your answer? (4 pts.) It would be better to use 4 mL aliquots of dichloromethane because with four substages of dissolving, it enables us to get more interactions between the caffeine in the tea and the dichloromethane. It is the same concept as washing the crystals from recrystallization with multiple aliquots of acetone to get purer crystals. 4. If one could not use sublimation for the purification of caffeine, would recrystallization or distillation be a better method to purify caffeine? Explain why. (4 pts.) Recrystallization is most likely a better method because recrystallization focuses on evaporating liquid solvents into atmosphere while leaving behind a solute while distillations are carried out to purify a liquid.

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

CHEM 230L: Organic Chemistry I Lab Chapman University 5. Why did you basify tea using Na 2 CO 3 ? (4 pts.) It is important to basify the tea using Na2CO3 because as the verb suggests, it makes the tea a base by deprotonating the organic acids and caffeine. This ensures that caffeine will fully dissolve in the dichloromethane while the anhydrous salts will not.