Cerritos Community College
Organic Chemistry 211 Laboratory
Isolation and Characterization of a Natural Product:
Caffeine.
N
NN
N
O
O
H3C
CH3
H3C
N
NN
N
H
purine
caffeine
O
OH
N
N
N
HN
2'-deoxyguanosine
5'-phosphate
H2N
O
OPOH
O
O–
In this experiment, the techniques of solid-liquid extraction and liquid-liquid extraction
will be used to isolate caffeine from tealeaves. A new purification technique, sublimation,
will be used to perform the final purification.
Caffeine is a member of the class of natural products called alkaloids, which contain
nitrogen. Other members of this class include morphine, mescaline, and strychnine. The
strong biological activity of these compounds has led to their thorough investigation by
many different disciplines. Caffeine possesses the oxidized skeleton of purine, a relative
of which can be found as a constituent of DNA (see above). Caffeine is found in many
plants with coffee and tea being the most familiar. A cup of coffee or tea provides a 25- to
100-mg “Dose” of caffeine, which stimulates the central nervous system in a widely
exploited manner.
From the preceding, it is not surprising that caffeine is soluble in hot water, but it is also
soluble in dichloromethane, allowing the following extractive protocol to isolate it. This
two-step extractive isolation assures that ionic species remain in the aqueous layer while
taking advantage of the swelling that water causes in the tea leaves. Simply extracting the
tealeaves with dichloromethane directly is ineffective. The sodium carbonate added to the
water during the “steeping” stage is to insure that the caffeine and organic acids are
deprotonated. Thus, caffeine will be free to dissolve in dichloromethane while the
carboxylate salts will not (see Experiment 3). The caffeine supplied by extraction is fairly
pure, but sublimation will further purify the material in a procedure that is effective with
the small amounts obtained here.
Procedure
With care, measure out 1-2 grams of tealeaves. To a 100 ml round bottom flask, mass 1.1
g of anhydrous sodium carbonate, and then add 10 mL of deionized water. Heat this
mixture with the heating mantle to dissolve the sodium carbonate. Add the tea to this
solution, in the Erlenmeyer flask. Add a water jacketed condenser standing upright or
vertical so that all vapors condense and flow back into the mixture. Heat the mixture to a
gentle boil. Maintain constant volume by replacing any water that has escaped as vapor.
After 30 minutes of heating, cool the flask to room temperature and transfer the aqueous
extracts (after vacuum filtration) to a separatory funnel. Try to pour the liquid onto the
funnel before the solid portion which may clog the pores of the filter paper. To assure that
