The Extraction of Caffeine from Tea By: Courtney Lecker, Nick Johnson, and Courtney Tharp
Purpose:
The purpose of this experiment was to extract caffeine from tea using various extraction methods.
Discussion: Several organic compounds of interest are produced in plants and animals as natural products, such as the stimulant caffeine, salicylic acid, a component component in the synthesis synthesis of aspirin, and tamoxifen, an anti-cancer drug. You must be able to isolate these specific compounds from the hundreds of other compounds in their natural resources in order to extract them. Luckily, cellulose (figure 1) is a major component of tea leaves. Cellulose is an insoluble polymer of glucose. Caffeine (figure 2) is water soluble. That difference in solubility can be used an advantage when separating caffeine from tea leaves by using simple organic extraction procedures and hot water.
O
H3C
CH 2OH O
H H HO R
H O
O
H H
OH H
H
OH
H
OH H O
CH 2OH O
H
H
H HO
R
CH3
N N
H
O
CH 2OH
O
H N
H
OH
N
O
CH3
Figure 1: cellulose
Figure 2: caffeine
Objectives: In this lab, you will... wi ll... extract caffeine from tea leaves. assess the purity of the caffeine. calculate the percent of caffeine in a tea bag.
Materials: 50, 100, 400 mL Beakers 1 Tea Bag – string string and tag removed 10 mL Graduated Cylinder 1 M Na 2CO3 2 5 mL Centrifuge Tubes Aluminum Foil (10 cm X 10 cm) Small Test Tube w/ cork stopper Ethyl Acetate Stirring Rod Na2SO4 Analytical Balance Sand Beaker Tongs Ice Crucible Tongs Paper towels Scoopula Plastic Pipet Hot Plate Centrifuge Safety Goggles
Safety: Wear safety goggles at all times. ti mes. No open flame is to be used in organic lab. Many organic compounds are flammable
Procedure: Part 1: Tea Extraction Find and record the mass of a tea bag with tea. Record the mass of an empty tea bag from the chalkboard. Place 10 mL of a 1 M Na2CO3 solution in a 50 mL beaker. beaker. Place the beaker on a hot plate. Pinch the top of the the bag with a piece of Al foil. Put the bag into the solution, but wrap the Al foil around the top of the beaker. This will keep the bag off of the bottom of the beaker. Poke a small hole in the Al foil to allow steam to escape, and to add distilled water to the solution as needed to maintain the 10 mL level. Boil for 5 minutes. DO NOT ALLOW THE SOLUTION SOLUTION TO BOIL OVER. OVER. Carefully remove the beaker from hot plate using beaker tongs. Allow to air cool for a few minutes, then cool to room temperature quickly using an ice bath. Remove the foil and the bag. Squeeze out excess fluid from tea bag with crucible tongs being careful not to break the bag. Discard the tea bag. You should have no more than 8 mL of solution. If you have more, boil off more water water to concentrate the solution. If you need to boil longer, make sure the outside of the 50 mL beaker is dry before placing placing it on the hot plate. plate. Be sure to cool the extract extract to room temperature in ice bath.
Diagram 1: (without the tea bag)
Part 2: Ethyl Acetate Extraction Add 3 mL of ethyl acetate to the solution. Gently swirl the beaker for ~30 seconds. If the beaker is shaken vigorously, the contents may spew out. Vigorous shaking may cause the formation of an emulsion, which is more difficult to separate separate.. Add half of the solution to a 5 mL centrifuge tube, and the other half to a second 5 mL centrifuge tube. Make sure the volumes are exactly equal. Be sure to balance the centrifuge by putting the tubes in opposite holes. Centrifuge the mixture for 4 minutes. Remove tubes from from centrifuge. Using a plastic pipet, pipet, carefully remove the clear upper layer of liquid. Squeeze the bulb of the pipet before before putting the tip of the pipet pipet into the liquid. Put the tip all the way to the bottom of the clear layer and release the bulb slowly. This will be a mixture of caffeine caffeine and ethyl acetate. acetate. Place this liquid into a small test test tube. Remove as much much of the clear layer as possible. Pour the dark layer back into the beaker. Repeat steps 4 – 7 7 without cleaning the centrifuge tubes or the beaker. After each extraction, be sure to pipet the clear top layer into your test tube. After the third extraction, discard the lower dark layer down the sink with plenty of water.
Diagram 2:
Part 3: “Drying” and Evaporating the Ethyl Et hyl
Acetate/Caffeine Mixture Add a small amount (1/2 pea-sized) of Na 2SO4 to your test tube. Swirl gently. The crystals will clump. Continue to add small amounts of crystals to the test tube until the addition of new crystals does not produce more clumping, or until you cannot add any more to the test tube. Using the stirring rod, decant the fluid portion of your test tube into a 100 mL beaker by carefully pouring the fluid along the stirring rod. Avoid getting any crystals of Na2SO4 into the beaker. After the decanting process is completed, the ethyl acetate must be carefully and slowly evaporated leaving only only the crude caffeine behind. Place the 100 mL beaker in a sand bath (400 mL Beaker ~1/3
full of sand) and heat heat to ~100˚C. Gently swirl the
beaker in the sand bath. Just as the solvent has evaporated, remove the beaker. The crude caffeine will coat the bottom of the beaker.
Diagram 3:
Part 4: Caffeine Sublimation Assemble a sublimation apparatus as follows: (inside and out) a 50 mL beaker. Record its Clean and dry (inside mass. Place the 50 mL beaker inside the 100 mL beaker containing your crude caffeine. This is your sublimation apparatus. pl ate and begin Place the sublimation apparatus on a hot plate heating. Fill the small beaker with chips of ice. Be careful not to let ice or water fall into the larger la rger beaker. Continue heating until the sublimation process is complete (all the crude caffeine is off of the outer beaker). When heated, the pure caffeine will sublime subl ime and deposit on the outside of the 50 mL beaker. Carefully observe the the sublimation process occurring between the 50 and 100 mL beakers. Remove the apparatus from the hot plate with beaker tongs and allow to cool. Remove the inner beaker very cautiously and carefully pour off the ice water making certain no water comes in contact with the sublimed caffeine crystals. towel. Find Dry the inside of the 50 mL beaker using a paper towel. and record the mass of the beaker with the caffeine caff eine on its bottom. Scrape the product from the beaker into a small test tube. Keep your caffeine for the TLC lab.
Diagram 4:
Data: Throughout this lab, we collected various measurements of the caffeine and other objects to help with our calculations.
Mass of the teabag:
2.4738 g
Average mass of an empty teabag:
0.1749 g
Mass of tea:
2.2989 g
Mass of 50 mL beaker:
30.2057 g
Mass after sublimation:
30.2157 g
Mass of caffeine:
0.0070 g
Calculations: Finding the mass of tea in the teabag: Mass of the teabag – Average Average mass of an empty teabag 2.4738 g – 0.1749 0.1749 g = 2.2989 g of tea Finding the mass of caffeine: Mass after sublimation – Mass Mass of 50 mL beaker 30.2157 g – 30.2087 30.2087 g = 0.0070 g Percent of caffeine in one bag of tea: (mass of caffeine/mass of tea) x 100% (0.0070 g / 2.2989 g) x 100% 0.30% caffeine per teabag
Error: Absolute error: |Accepted value – Experimental Experimental value| |0.055 g – 0.0070 0.0070 g| = 0.048 g Percent error: (Absolute error / Accepted value) x 100% (0.048 g / 0.055 g) x 100% = 87% error
Conclusion:
In this lab, we had h ad to find the percent of caffeine in a teabag. Throughout the lab, we encountered a few difficulties and problems that could have raised our percent error. One of the errors that occurred took place in step step three. When we had to to
add Na2SO4 to the test tube, we couldn’t add the Na2SO4 until it didn’t clump cl ump because we had too much solution in the
test tube. This would have been random error error due to the excess of the solution. This would have also raised the percent
error because the Na2SO4 wouldn’t be able to accumulate as much and dry the ethyl ethyl acetate. acetate. Another problem we had was during step step two. We had to centrifuge the solution and
pipet the upper upper layer. When pipetting, we couldn’t extract extract all of the liquid. This means we wouldn’t have removed all of the
ethyl acetate, acetate, which contains contains the caffeine. caffeine. This would have personal error and it would raise our error by not n ot extracting all the caffeine. Overall, I would say say our results could have been been better. This causes us to not be pleased with our results. results. If we had to do it over again, I believe bel ieve we would try to centrifuge more to extract more caffeine, and to also use a larger test tube so we
wouldn’t run out of room.
