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Experiment 3: Isolation of Caffeine from Tea
I
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The caffeine was then confirmed using
Thin Layer Chromatography, as well as the melting point determination, and the Retention
Factor of the standard and the extract was computed and thus compared
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Introduction
The goal of the experiment was to obtain a percent yield of caffeine and confirm its
presence through Thin Layer Chromatography (TLC)
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The purpose of the
sodium carbonate is to prevent tannins to combine with caffeine
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The beaker is then heated for 20 minutes, but not vigorously as it
may lead to frothing and thus sample loss
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To obtain residue, the tea bags are pressed
with a test tube and pour the liquid obtained into the separatory funnel
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Afterwards,
the black solution was washed with methylene chloride five times
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Instead, inverting the funnel slowly or using a
test tube to pop the emulsions may be used
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The organic layer is then collected and dried over
sodium sulfate and it is then decanted into a round bottom flask, ready for distillation
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The solution is then transferred to a pre-weighed beaker then the round bottom
flask is rinsed with 2mL methylene chloride then put into the same beaker
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It is then
weighed and the second part, TLC, is then performed
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A TLC plate was obtained and a line was drawn from its
two
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Using two separate capillary tube, spot the two labels from the standard and the
extract
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The mixture must not go over the bottom
line
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The retention factor of each spot is then computed and
compared
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III
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Beaker
Wt
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Caffeine
%Caffeine
Retention Factor of Standard
Retention Factor of Extract
Accuracy
Melting Point

33
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77g
(33
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70)=0
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07g/0
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44%
(0
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09g per tea bag; there are 4 tea bags)
(1cm/2
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36 cm
N/A
N/A
236
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36-0
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36 x 100 = 80
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44%
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Using the Melting Point Determination, the result was 236
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A factor that could have affected the TLC results is not
drying the TLC plate after soaking it in the benzene/ether/acetic acid/methanol mixture
before putting in under the UV lamp
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A % error of 80
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IV
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Caffeine content is
reported to be at 19
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6 oC is close to that of the standard (238 oC),
but it was not confirmed to have the presence of caffeine through Thin Layer
Chromatography because there were no spots for the extract
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56%
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Answers to Questions
1
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Suggest two ways of purifying caffeine
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A cup of coffee contains about three to four times as much caffeine as a cup of tea even
though the caffeine content of tea leaves is greater than that of roasted coffee beans
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cup, where the same size cup
of coffee tends to have about 80-135mg of caffeine; but by dry weight, tea actually contains
more caffeine than coffee
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cup of tea
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The brewing method for tea [and to some degree for coffee] can have a large effect on the
caffeine content
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3
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If 200mL of
coffee solution contains 0
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80-x))
X=0
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80g - 0
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18g caffeine in aqueous layer
10=(x/30)*(200/(0
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48g à 0
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48g = 0
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32-x))
X=0
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32g - 0
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13g caffeine in aqueous layer

The two 30mL’s gives a more complete reaction because more caffeine is extracted and less
of the caffeine is left in the aqueous layer
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Why was frothing expected as you heat the tea in aqueous base?
Because of the saponins, which have similar properties as a soap
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5
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Give reasons
why you had to distill the solvent
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The second is because it is highly
carcinogenic and toxic and inhalation of methylene chloride is more probable if a lot of
methylene chloride is evaporated
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References
[1] Guidote, A
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Experiencing Organic Chemistry
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Print
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Organic Chemistry Laboratory Website
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p
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d
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Accessed July 15, 2013
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chem
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ca/~orglabs/Techniques%20Extra%20Info/TLC
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The more polar compound will win this
compettion and adhere (adsorb) to the adsorbent, while the rest of the mixture will move
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Rf (retention or
retardation factor): is a measure of the distance travelled by the compound spot in relation to
the distance travelled by the eluent
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Technology Transfer Network Air Toxics Website
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p
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d
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Accessed July 15, 2013
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epa
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html>
The effects of chronic (long-term) exposure to methylene chloride suggest that the
central nervous system (CNS) is a potential target in humans and animals
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Animal studies have shown increases
in liver and lung cancer and benign mammary gland tumors following the inhalation of
methylene chloride

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