Extraction of Caffeine From Tea Leaves
Extraction of Caffeine From Tea Leaves
Extraction of Caffeine From Tea Leaves
INTRODUCTION
METHODOLOGY
The objective of this experiment is to isolate, purify, and extract caffeine from tealeaves.
Three (3) Bigelow green teabags were prepared for extraction then boiled (as shown in figure 2).
However, the liquid obtained from the boiling of green teabags is not yet the pure caffeine. To
maximize the liquid to be used in the following procedures, the teabags were filtered using a
filter paper and squeezed to release more of its liquid. The liquid obtained is then placed in a
separatory funnel with an addition of 20 mL of CH2Cl2 to extract the caffeine present in the tea
(as shown in Figure 3). The mixture was shaken well to
eradicate bubbles present in the mixture. No bubbles
must be present to avoid errors in the percentage yield of
caffeine. After the mixing process in the separatory
funnel, CH2Cl2 lower layer was drained from the mixture
and was collected in a clean flask. However, the water
layer was discarded. Moreover, the mixing process was
repeated thrice with 20 mL of CH2Cl2. The combined
CH2Cl2 was again placed in the separatory funnel for
further extraction though a different solvent was added
which is NaOH solution. After placing 6 mL of 6M
NaOH solution in the separatory funnel, the CH2Cl2 layer
is again collected in a clean flask and later on added a
half spatula of anyhd Na2SO4. It was then placed in a hot
water bath to transform the liquid to solid and to
evaporate the excess water in the mixture.
DATA SHEET
TREATMENT OF RESULTS
Weight of mortar with combined weight of tealeaves – weight of mortar = weight of combined
tealeaves.
114.12 g - 108.10 g = 5.82 g
Weight of Erlenmeyer flask with crude caffeine - Pre-weighed Erlenmeyer flask = Crude
caffeine
% yield = (pure caffeine + excess g from foil / combined weight of tealeaves) X 100
% yield = {[(16.4611 g – 16.4588 g) + (7.31 g – 7.19 g)] / 5.82 g } X 100
% yield = [(0.0023 g + 0.12 g) / 5.28 g] X 100
% yield = 2.10137457 %
% yield = 2.10%
DISCUSSION OF RESULTS
About 0.0023 g of pure caffeine was obtained in pure green tea unlike in black teas such
as Oolong tea, the grams of caffeine are much higher (). After boiling the teabags in a hot bath,
the liquid obtained was filtered to remove any insoluble material. The extracted liquid can be
further separated through liquid/liquid extraction using different solvents. This technique
selectively dissolves one or more compounds into an appropriate solvent. The solvents used in
this experiment are dichloromethane and NaOH solution. The liquid was extracted in a
separatory funnel with repetitions of 20 mL of CH2Cl2 instead 60 mL of CH2Cl2 at once in one
extraction because the more repetition of washing of CH2Cl2, the greater amount of caffeine will
be obtained. The two solutions then separate into two layers: the aqueous layer and the organic
layer. The separation of layers is due to their difference in solubility and difference in density (as
shown in Figure 5). The different layers can also be observed on their immiscibility. The
immiscible one is the aqueous layer, which is then discarded in the solution.
After the extraction process, the crude caffeine was further purified through sublimation
if impurities are non-volatile. Crude caffeine is place in an air bath with a “cool finger” on top.
The crude caffeine is then heated to sublimation. External heating drives the sublimation process.
The gaseous caffeine will be separated from the less volatile impurities and then forms crystal
caffeine deposits along the cool surface. For a substance to change phase into a gas, its molecules
must reach a vapor pressure equal to that of its external air pressure because a vacuum lowers the
air pressure, the caffeine can reach this vapor pressure at a lower temperature and bypass the
liquid phase (as shown in Figure 6)(Khan Academy).
Figure 6: Caffeine Phase diagram with the arrow indicating the path of the caffeine
sublimation.
To confirm if the obtained pure caffeine is free from impurities, the melting point of the
pure caffeine was determined using a melting point apparatus. Knowing the melting point of an
organic compound is essential in gauging its purity. This test is done because even small
quantities of impurities change the melting point or enlarge its melting range. The first point
where the pure caffeine turned black is at 223 degrees Celsius and it turned fully black at the
point of 235 degrees Celsius. This shows that pure crystalline substances have a clear, sharply
defined melting point (Stanford Research Systems).
The pure green tea yielded 2.10% pure caffeine, which shows that minimal caffeine but
close to its theoretical value of 2% present in this kind of tea. The extraction process was made
possible by the addition of CH2Cl2 or dichloromethane, which separated the organic layer from
the aqueous layer. This occurrence is due to the difference in solubility levels of the mixture
present and their visual representation that distinguished that there are two (2) dissimilar layers
present. The visual representation may be immiscible or miscible. In this experiment, the
aqueous layer or water layer was immiscible with CH2Cl2 resulting to an easier washing with
CH2Cl2 and separation of layers. The bubbles present in the separatory funnel must be released to
eradicate as much as possible the errors in obtaining the percentage yield of pure caffeine. Error
may also arise from the draining of the CH2Cl2 layer wherein some are still left in the separatory
funnel after repetitive extractions. In the purification process, there is a tendency that the pure
caffeine will not stick on the fitted inner tube or cold finger when not done properly. A well-
executed purification set-up is wherein the flask containing the crude caffeine is covered
properly, the cold finger was replaced consistently in a span of 35 minutes, and no water was
inserted inside the flask while the replacement of water in the cold finger was taking place. After
the air bath, the pure caffeine was scraped off on the cold finger and white substances remaining
on the flask was also scraped off. However, a problem may be encountered in the process of
scraping off the pure caffeine in the flask. The dirty light yellow substance or crude caffeine
might also be obtained because of its similarity in appearance to the pure caffeine. When the
crude caffeine is obtained together with the pure caffeine, the weight of pure caffeine might have
some impurities. To know if there are impurities in the pure caffeine obtained, the melting point
was determined. The melting point range recorded, which is from 223 degrees Celsius to 235
degrees Celsius, was not large but ideal enough to produce 2.10% from the theoretical yield of
2% pure caffeine in the green tea.
REFERENCES
[1] Experiment 2 – Isolation and Sublimation of Caffeine from Tea Leaves. (n.d.). Retrieved
from https://acrochem.sites.ucsc.edu/wp-content/uploads/sites/291/2015/11/Exp-
2- Isolation-and-Sublimation-of-Caffeine-from-Tea-Leaves-4.pdf.
[2] Experiment # 6 – Isolation of caffeine from tea leaves. (2003). Retrieved from
http://employees.oneonta.edu/knauerbr/chem226/226expts/226_expt06_pro.pdf.
[4] Postu, A. (2013). Isolation of Caffeine from Tea Leaves via Acid-Base Liquid-Liquid
Extraction. Retrieved from http://edspace.american.edu/ap7794a/wp-
content/uploads/sites/159/2015/03/Isolation-of-Caffeine-from-Tea-Leaves-via-
Acid-Base- Liquid-Liquid-Extraction.pdf.