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Microsoft word - caffeine.doc

Introduction In nature, a wide variety of compounds are produced by plants. These naturally-occurring compounds generally occur in a mixture in the plant tissue. Often, it is useful to extract these compounds for use in foods and drugs. The varying chemical properties of individual compounds allow chemical techniques to be developed to isolate the desired compound. Caffeine is produced by coffee and tea plants and is used as an analgesic, stimulant, and diuretic. It stimulates the heart, the central nervous system, increases glomerular filtration rate, and its use is widespread throughout the world. The chemical properties of caffeine, a bicyclic ring containing two nitrogen atoms (purine), allow it to be quite soluble in water and methylene chloride. Also, weak intermolecular interactions allow it to sublimate, or pass directly from the solid phase to the gas phase. These properties make it relatively easily to extract and purify from natural sources. Table of Reagents 1. Wear Goggles 2. Avoid ethyl acetate vapors, dry TLC plates under hood 3. Do not look directly into UV lamp 4. Avoid skin contact with Methylene Chloride Procedure Two tea bags were placed in a beaker containing 15 mL of boiling water and 2 g of dissolved sodium carbonate. The solution was allowed to steep for 5 minutes. A suction filtration apparatus was setup with a suction flask and a buchner funnel. The steeped tea solution was poured through the funnel. The tea leaves were then washed with about 10 mL of hot water. When about 25 mL of solution had been obtained, the contents was transferred to a 50 mL Erlenmeyer flask and 400 mg of NaCl was dissolved in it. The beaker was placed in an ice bath and cooled to about 5 C, then washed with
approximately 5 mL methylene chloride. The flask was sealed with a stopper, agitated,
then allowed to vent and settle into an emulsion. The layer of methylene chloride was
then drawn out with a pipette and placed into a filter flask.
The methylene chloride wash was repeated three times and the 15 mL of this solvent was
collected. A few drops of the solvent were placed on a TLC plate next to a control sample
of pure caffeine, and this plate was placed in a jar containing ethyl acetate. The flask was
then heated to boil off the methylene chloride and leave behind the caffeine-containing
residue. The flask was weighed and compared to the weight of the empty flask to
determine the mass of the material extracted from the tea.
A test tube was inserted into the neck of the filter flask and the junction was sealed with a
rubber filter adapter. The side arm was sealed with a pipette bulb. Ice was packed down
into the length of the test tube and continuously replenished as heat was applied to the
flask. A temperature was maintained that was below 220 C, to sublimate the Caffeine for
recrystallization onto the cold test tube. When a sufficient amount of caffeine had
crystallized onto the test tube, it was carefully removed and scraped onto a watch glass.
Note: pure caffeine was added before the sublimation process began in order to gain a
higher yield for melting. The caffeine crystals were crushed and packed into a closed-
end capillary. The capillary was placed in a Mel-temp and slowly heated to determine
the melting point of the collected solid.
Data and Observations
TLC Plate:
Two large dots were observed under UV light.
Rf (pure caffeine):
.23
Rf (extract)
.28
Weight of extracted material:
.41 g
Observed melting point caffeine purified by sublimation:
237 C
Results and Discussion
TLC indicated that the material extracted contained mostly caffeine, as the Rf values were
relatively close. Approximately 410 mg of material was extracted by the solvent, a
reasonable level of caffeine for two tea bags. The observed melting point was 237 C, one
degree off from the standard melting point value of 238 C. It is likely that some
impurities were present in the extract, as it is likely that tea does contain some other compounds were eluted by the water and were soluble in the methylene chloride, and since the technicians were not professional organic chemists. The small disparity in the melting point may have several causes. It is possible that the temperature on the thermometer bulb could have been slightly different than the temperature inside the capillary, or that a few impurities such as dust accumulated on the watch glass and were packed into the capillary with the caffeine, causing the substance to melt at a lower temperature. Conclusion This experiment demonstrated that caffeine (note: tea actually contains theophylline) possesses chemical properties that allow it to easily be extracted with the proper solvents. Sublimation is an extremely effective method for purification, as a sublimated material in the gaseous phase will recrystallize in pure form if properly manipulated, such as with a low temperature on a glass surface. Identification by melting point is useful for determining the purity of a sample.

Source: http://webpages.uah.edu/~gas0001/BYS119L/caffeine.pdf

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