The Isolation of Caffeine from Tea

 

This work is dedicated to all the students who have spent countless hours awake thanks to the effects of Caffeinated drinks, and to my mother, for allowing me access to her tea collection.

- Victor Rodriguez

 

Abstract: The purpose of this lab was to determine the Caffeine content, by mass, of two brands of tea. The brands of tea which were chosen to be compared were Earl Gray and Red Rose. During the lab, a cup of each kind of tea was made and then strained. For each cup, straining was followed by three washings of Chloroform, two washings of Sodium Hydroxide, and one washing of distilled water, with all washings taking place inside a separatory funnel. The remaining substance was then evaporated until only white crystals remained, which were considered to be pure Caffeine. The Caffeine was massed, and compared to that of the other brand. It was concluded that Red Rose brand tea contained slightly more Caffeine (0.036 g per tea bag) then Earl Gray (0.031 g per tea bag).

 

Table of Contents:

A. Background Information

  1. Theory
  2. Problems and Variables
  3. Hypothesis

B. Experimental

  1. Materials
  2. Procedure
  3. Safety Points

C. Observations

D. Analysis

E. Conclusion

F. Bibliography

G. Appendix

 

A. Background Information

i. Theory:

Caffeine is a very common substance and is found in coffee, tea, soft drinks, chocolate, and "stay-awake" pills such as Vivarin. It can be synthesized or isolated from natural sources. Caffeine constitutes approximately 4% of tea and coffee leaves, and is also found in cola nuts and cacao beans.

In Humans, Caffeine acts to stimulate the heart, central nervous system, and the respiratory system. Blood pressure is increased by its use, since heart rate is increased, as is contraction force and volume output. It is a diuretic and has the effect of delaying fatigue. Caffeine has a bitter taste but no smell. There is research linking high Caffeine consumption in pregnant women to the malformation of their children.

Caffeine is addictive to Humans. Regular consumption of drinks and food containing the drug reduce sensitivity to its effects, causing the body to become over-sensitive to adenosine. This causes a decrease in blood pressure, severe headaches, dizziness and tiredness. People have been known to die after ingesting large quantities of Caffeine, but it would take approximately 100 cups of coffee to reach these levels.

Caffeine is an alkaloid, and, more specifically, a member of the methylxanthines. Thus, Caffeine is closely related to theophylline and theobromine. Pure Caffeine takes the form of white, hexagonal crystals, which can be broken into a soft powder. It has a melting point of 235 oC - 238 oC, and a molecular weight of 194.19 g/mol. It is easily soluble in Chloroform and partially soluble in water.

Caffeine has the chemical name "3,7-dihydro- 1,3,7-trimethyl- 1H-purine- 2,6-dione" and the molecular formula C8H10N4O2. The image of Caffeine in the appendix was generated by RasMol Version 2.6. Oxygen atoms are shown in red, Nitrogen atoms in blue, Carbon in gray, and hydrogen in white.

The isolation of Caffeine from tea is a simple-seeming experiment, which in fact makes use of a number of rather advanced chemical processes. To isolate the Caffeine in a sample of tea, it is necessary to chemically separate the Caffeine from the rest of the tea prior to evaporation. This process is known as ‘extraction.’ Extraction is a chemical method of separating a specific component of a solution from the rest of the solution. This is done by using a solvent (in this case Chloroform) in which the substance to be isolated is very soluble, while the rest of the solution is not as soluble.

For the purposes of this experiment, Chloroform was chosen as the solvent because Caffeine is very soluble in this substance. Thus, when the separatory funnel is used, the Caffeine in the tea dissolves into the Chloroform and the rest of the tea can be discarded. This is done three times so that the amount of Caffeine left in the discarded tea is minimized. This is followed by two washings with Sodium Hydroxide and one with water. It is believed that the Sodium Hydroxide weakens the attraction Chloroform has on Caffeine, allowing the Caffeine to be isolated more easily later on.

ii. Problem and Variables:

At standard temperature and pressure, what is the Caffeine content, by mass, of two kinds of Caffeinated tea? In this experiment, the controlled variables are the temperature of the teas, the pressure under which the experiment is carried out, the sizes and shapes of all containers, and the amount of time that each step in the procedure is allowed to proceed. The manipulated variable is the kind of tea used in each phase of the experiment. The responding variable will be the determined Caffeine content of each of the teas.

iii. Hypothesis:

Based on the accepted value that 7 oz of tea contain between 30 and 70 mg of Caffeine, it is expected that the 200 g sample of tea prepared will contain approximately 150 mg (0.150 g) of Caffeine. This number was derived by converting 7 oz to 200 g, averaging the Caffeine content, and then multiplying the accepted Caffeine content by three because three bags will be used.

B. Experimental

i. Materials:

This experiment was performed simultaneously by two students, so that in this way, the results could be shared for comparative purposes and time would be saved. Thus, the materials and procedure are written from the point of view of one student, but in fact, each element should be doubled. The following materials were used:

ii. Procedure

The following procedure is a summary of that found in the original Project Plan, with modifications to compensate for actual events.

Mass of three tea bags of Red Rose tea was obtained using the electronic scale. 200 g of distilled water was heated to 99 oC in a beaker using the hot plate. The bags were placed into the beaker and swirled for 60 seconds, at which time the three bags were removed and the liquid remaining in the bags squeezed back into the beaker using the two glass slides. The beaker was placed into the cold water bath in the large plastic container. When the temperature had reached 26 oC, the tea was strained using filter paper.

120 ml 6M NaOH was prepared by dissolving 28.7 g of solid NaOH into 120 ml of distilled water. This was set aside. The contents of the tea beaker were placed into the separatory funnel and allowed to settle. 20 mL of CHCl3 was added and the funnel was inverted back and forth ten times, stopping every three times to allow gas to escape. The organic layer in the funnel was released into a new beaker. The 20 mL CHCl3 washing was repeated twice more, each time releasing the organic layer into the second beaker. After the three washings, the contents of the separatory funnel were discarded and the contents of the second beaker were placed into the separatory funnel. Two washings with 20 mL NaOH were done, followed by one washing with 20 mL of distilled water.

Next, the contents of the separatory funnel were poured into the third beaker. This was placed over the hot plate and the temperature was set to "6". When all the liquid had evaporated, the beaker was massed on the electronic scale. Then, the white residue was scraped off the bottom of the beaker and onto a massed piece of paper. Both the clean beaker and the piece of paper with the white residue were massed. In this way, the mass of the residue was obtained in two separate ways.

iii. Safety Points

See attachment OAC ISP Laboratory Investigation Safety Report.

C. Observations

Data Recorded During the Isolation of Caffeine from Tea

Tea Brand

Red Rose Orange Pekoe Tea

Combined weight of 3 tea bags (g)

10.4

Amount of water used to make tea (ml)

202

Temp. of water when tea bags were added (oC)

99

Temperature of water after cold-water bath (oC)

26

Weight of Caffeine crystals by beaker method (g)

0.104

Weight of Caffeine crystals by paper method (g)

0.113

In addition to the tabular observations, the tea was noted to be dark orange in colour, and to have a cloudy appearance. Straining the tea collected only a minimum of physical residue. During the extraction process using the separatory funnel, a dark, spongy layer was observed between the clear organic layer and the brown tea layer. When isolated, the Caffeine crystals were a pale yellow colour, and broke apart easily when probed with the powder scoop.

 

D. Analysis

Data Calculated from Observations

Source of Data

Red Rose Tea

Partner’s Experiment (Earl Gray Tea)

Average Amount of Caffeine Isolated (g)

0.109

N/A

Caffeine Isolated Per Tea Bag (g)

0.036

0.031

Caffeine Content by Mass (%)

1.04

N/A

As can be seen in the table above, Red Rose Tea appears to have a slightly higher Caffeine content by mass than Earl Gray. As well, the average amount of Caffeine isolated is similar to the original hypothesis for this amount, which was 150 mg, or 0.150 g. The official amount of Caffeine in instant tea is 0.040 g, leading one to believe that not all of the Caffeine in the tea was successfully isolated. However, according to one source, "The variability in the amount of caffeine in a cup of coffee or tea is relatively large even if prepared by the same person using the same equipment and ingredients day after day." This would lead the experimenter to believe that perhaps most of the Caffeine was isolated.

In addition, the final steps of this lab were not performed according to established procedure. Rather than use a sublimation process to generate the Caffeine crystals, the final solution was simply boiled until only white crystals remained. It is possible that some of the Caffeine could have been lost to evaporation in this way. Neither was any testing done on the white powder that was collected. It is possible, even likely, that this powder was not pure Caffeine, but in fact contained other impurities found in the tea.

In a separate mini-experiment, which was not described in the Procedure or accounted for in the Materials, a second cup of tea was prepared as described in the Procedure. However, instead of using the cold-water bath and continuing as before, the tea was simply kept boiling until all the liquid had evaporated. As expected, white crystals were not formed on the bottom of the container. Instead, a sticky, dark brown sludge coated the entire beaker and later proved difficult to clean. This mini-experiment proves that the extraction process is necessary for pure Caffeine crystals to be successfully obtained.

It was noticed during the steps of the experiment involving the electronic scale that the number displayed never seemed to reach equilibrium. Even when the furniture containing the scale was closed and no one was moving nearby, the number on the display continued to fluctuate within a range of approximately 0.01 g. Thus, even though the Caffeine was massed at 0.109 g, it could actually have been anywhere between 0.099 g and 0.119 g.

It is also possible that some Caffeine was lost during the use of the separatory funnel. To insure a pure result, the separatory funnel was not emptied completely of the organic layer. Almost 1 cm of organic layer was left in the funnel after each release. Every time the solution was transferred from one beaker to another, some Caffeine could have been left behind coating the container. Finally, some Caffeine might have been lost or destroyed during the evaporation process.

This experiment has been described by one source as "a popular second-year organic experiment." Since the experimenter is currently working with a high school level of chemistry knowledge, it should not be surprising that some of the theory behind this experiment has proven confusing. It is believed that the experiment was carried out to the best of the experimenter’s ability, however it is possible that with more experience and by using more sophisticated equipment, a more satisfactory result might have been obtained.

E. Conclusion

In consideration of the numerous sources of error, this experiment has been a success. Pure, or mostly pure, Caffeine crystals have been isolated from a cup of tea and weighed. This value was similar to the accepted Caffeine content of tea, thus the results supported the original hypothesis.

Caffeine is a substance with a variety of uses. From medicines to beverages to foods, Caffeine is amoung the most popular natural products used today. However, Caffeine also acts to increase blood pressure and is addictive. Because of its effects, Caffeine is also used in the treatment of migraines and asthma relief. However, it has recently been linked to birth defects and cancer. People who have acquired a tolerance to the drug experience headaches, dizziness, and vomiting when they withdraw. For these reasons, the full effects of Caffeine as well as the amount contained in various products is very important to know.

Extraction is a process that can be used to determine the content of a certain substance within a solution. However, each extraction process is different. To take only one example, the extraction of Caffeine from various substances, such as tea, coffee, and Coca Cola, requires different extraction techniques, since the composition of the solution is different in each case. It would be beneficial to find a process that would extract a substance regardless of the solution it is part of. It would also be interesting to learn of Caffeine alternatives. Perhaps in the future a substance will be developed with the positive effects of Caffeine, but without the addictive qualities or possible side effects of this substance. In the meantime, it seems that students will continue to make use of the priceless effects of Caffeinated drinks.

F. Bibliography

  1. "BridgeTown Coffee Sundries" BridgeTown Coffee (1998): 2pp. Online. Internet Explorer 5.00. May 19, 2000. Available: http://www.bridgetowncoffee.com/sundry_3.html
  2. "Caffeine." Microsoft Encarta 97 Encyclopedia. CD-ROM. Microsoft Corporation. 1997.
  3. "Caffeine Extraction from Tea - A Simplified Procedure" Department of Chemistry at Okanagan University College (December 1996): 3pp. Online. Internet Explorer 5.00. May 8, 2000. Available: http://www.sci.ouc.bc.ca/chem/faculty/neeland2.html
  4. "Caffeine Isolation" Organic Chemistry Laboratory (March 2000): 1pp. Online. Internet Explorer 5.00. May 19, 2000. Available: http://www.brynmawr.edu/Acads/Chem/mnerzsto/caffeineisolationflowchart.htm
  5. "Experiment 11B Isolation of Caffeine, pp. 232-237" Chemistry 25 - Chemistry of Organic Compounds (November 1999): 2pp. Online. Internet Explorer 5.00. May 12, 2000. Available: http://www.chem.brown.edu/chem25/caffeine.html
  6. "Extraction." Microsoft Encarta 97 Encyclopedia. CD-ROM. Microsoft Corporation. 1997.
  7. "Frequently Asked Questions about Caffeine" Coffee Page (1998): 20pp. Online. Internet Explorer 5.00. May 8, 2000. Available: http://aomt.netmegs.com/coffee/caffaq.html
  8. "Isolation of Caffeine" Chemistry 211: 1pp. Online. Internet Explorer 5.00. May 19, 2000. Available: http://www.facstaff.bucknell.edu/casteel/chem211/labs/caffeine.html
  9. "Isolation of Caffeine from Coffee Using Solid Phase Extraction with C-18 Silica" Undergraduate Organic Chemistry Laboratory Experiments (February 1996): 2pp. Online. Internet Explorer 5.00. May 12, 2000. Available: http://www.dartmouth.edu/academia/chem/chemexp/Expt5.html
  10. "MATERIAL SAFETY DATA SHEET Sodium Hydroxide" PROSCITECH Microscopy & Electron Beam Instrument Supplies (October 1997): 4pp. Online. Internet Explorer 5.00. May 21, 2000. Available: http://www.proscitech.com.au/msds/c200.htm
  11. "MSDS Dichloromethane(DCM)" MSDS for Solvents and Reagents (January 1997): 3pp. Online. Internet Explorer 5.00. May 21, 2000. Available: http://glenres.com/ProductFiles/MSDS/f_mDichloromethane.HTML
  12. New Lexicon Webster’s Dictionary of the English Language Deluxe Encyclopedic Edition, The. New York: Lexicon Pulications, Inc. 1987.
  13. Rosenberg, Jerome L. & Epstein, Lawrence M. College Chemistry Eighth Edition. Toronto, Ontario, McGraw-Hill, 1997.
  14. "Tea." Microsoft Encarta 97 Encyclopedia. CD-ROM. Microsoft Corporation. 1997.
  15. Wingrove, Alan S. & Caret, Robert L. Organic Chemistry. New York, Harper & Row, 1981.


Caffeine Molecule Observed Caffeine Crystals