extraction of caffeine from tea
Shanbhag
Caffeine Extraction
2006
Extraction of Caffeine from Tea
Purpose is to learn some of the basic techniques of organic chemistry:
extraction, filtration, evaporation of a solvent and drying methods-in the context of
working with a chemical known to all, caffeine.
O
H3C
N
O
O
CH3
N
N
H
N
O
CH3
N
N
CH3
N
N
CH3
Caffeine (Coffee)
Theobromine(Chocolate)
Pure caffeine is a white, tasteless substance that makes up as much as 5% of
the weight of tea leaves. By structure, caffeine is closely related to the purine bases,
guanine and adenine, found in deoxyribonucleic acids (DNA).
N
N
N
N
H
Purine
O
H3C
O
OH
CH3
N
N
N
N
N
N
H2N
NH2
N
N
H
N
N
N
N
H
CH3
Caffeine
Guanine
Adenine
Shanbhag
Caffeine Extraction
2006
A number of plants contain caffeine and its use as a stimulant predates
written history. The origins of tea and coffee are lost in legend. In addition to being in
tea leaves and coffee beans, caffeine is a natural constituent of kola nuts and cocoa
beans. Cola soft drinks contain 14-25 mg of caffeine per 100 mL (3.6 oz), and a
sweet chocolate bar weighing 20 g (0.7 oz) contains about 15 mg of caffeine. "Stay
awake" preparations such as No Doz have caffeine as a main active ingredient.
The caffeine content of tea leaves depends on the variety and where they
were grown; most tea has 3-5% by weight. Coffee beans contain only about 2%
caffeine by weight, yet a cup of coffee has about 3.5 times as much caffeine as does
a cup of tea. How can this be? Coffee is usually boiled in its brewing or else ground
extremely fine: tea leaves are simply steeped in hot water for a few minutes
Furthermore more ground coffee than tea is used to brew one cup of beverage. A
cup of tea contains about 25 mg of caffeine.
The biological action of caffeine includes cardiac and respiratory stimulation,
and it has a diuretic effect as well. Tea also contains a trace of the alkaloid
theophylline, which is similar in structure to caffeine; it stimulates muscle action and
relaxes the coronary artery. Theophylline also has veterinary applications as a
diuretic and a cardiac stimulant.
O
H3C
O
O
H
N
N
N
CH3
N
R
N
O
N
R'
N
Xanthine: R = R' = R'' = H
Caffeine: R = R' = R" = CH 3
N
Theophylline: R = R" = CH 3, R' = H
Theobromine: R = H, R' = R" = CH 3
R"
Theophylline
Obtaining pure caffeine from tea requires a method for separating caffeine
from the other substances found in tea leaves. Cellulose, the primary leaf
component, poses no problem, because it is virtually insoluble in water. However, a
large class of weakly acidic molecules called tannins also dissolve in the hot water
used to dissolve the caffeine from tea leaves. Tannins are colored compounds
having molecular weights between 500 and 3000 and phenolic groups that make
them acidic. If calcium carbonate, a base, is added to tea water, calcium salts of
these acids form in the tea solution. The caffeine can then be separated from the
alkaline tea solution by a process of extraction using dichloromethane, an organic
solvent in which caffeine readily dissolves. The calcium salts of the tannins remain
dissolved in the aqueous solution. Flavinoid pigments and chlorophylls also
contribute to the color of a tea solution. Although chlorophylls have some solubility in
dichloromethane, the other pigments do not. Thus, the dichloromethane extraction of
a basic tea solution removes nearly pure caffeine, which has a slight green color
from the chlorophyll impurity.
Shanbhag
Caffeine Extraction
2006
After the extraction procedure, the organic solution of dichloromethane and
caffeine is dried with an anhydrous inorganic salt. Crude caffeine is recovered as a
solid residue by evaporation of the dichloromethane.
The solubility of caffeine in water at 20°C is 2.2 g per 100 mL, so there is no
problem in keeping it in water solution while you filter off the spent tea leaves and
calcium salts. Caffeine is far more soluble in dichloromethane: 10.2 g per 100 mL at
20% So this extraction takes advantage of distribution coefficient (k) of 4.6. To
Conserve dichloromethane and time, we will settle for two 15 mL extractions of the
aqueous tea solution. This method does not extract all the caffeine but yields more
than enough for the purification step. The 10 g of tea that you boil with water should
contain at least 300 mg of caffeine. You will be able to recover 10-30% of this
amount.
A comment about filtering the boiled tea solution should be made before you
begin. If it is filtered when it is too hot, messy bubbling occurs in the filtrate and
some solution may be lost. Yet if it is filtered when it is too cool, the gelatinous
material that separates on cooling will clog the pores of the filter paper. Fast, non
retentive filter papers such as Schleicher and Schuell (S&S) No. 410 and Whatman
No. 54 work well.
Safety:
Dichloromethane is toxic, an irritant, absorbed through the skin, and harmful if
swallowed or inhaled. Use it in a well ventilated hood. Wear gloves and wash
your hands thoroughly after handling it.
Solid caffeine is toxic and an irritant. Avoid contact with skin, eyes, and clothing
Place approximately 10 g of tea leaves in a 400-mL weighed (tared) beaker;
record the mass of the tea leaves. If you use teabags, four bags should contain
about 10 g of tea; remove the tea leaves from the bags and place the tea in the
beaker. Add 4.8 g of. Calcium carbonate and pour 100 mL of water over the tea. Boil
the mixture gently on a hot plate for 15 min, stirring every minute or two with a
stirring rod.
Let the tea mixture cool to about 55oC, then filter it, using vacuum filtration
through S&S No. 410 or Whatman Filter paper. Pour the tea mixture in the Buchner
funnel in two portions. If the filter paper clogs while the first portion is filtering,
replace it with a fresh piece before filtering the remainder of the tea mixture.
Cool the filtered solution to 15-20°C by adding a few ice chips. Set up a 125-mL
separatory funnel and pour the cooled tea solution into the separatory funnel (be
sure the stopcock is closed). Add 15 mL of dichloromethane to the funnel. Stopper
the separatory funnel, hold the stopper firmly in place with your index finger, and
invert the funnel. Open the stopcock to vent the vapors. Rotate the inverted funnel
for 2-3 min, so that the two layers swirl together many times, opening the stopcock
frequently to vent the funnel.
Allow the layers to separate and then drain the dichloromethane layer into a 50mL Erlenmeyer flask. If a small emulsion layer is present at the interface between
the organic and aqueous phases, add it to the Erlenmeyer flask. Cork the
Shanbhag
Caffeine Extraction
2006
Erlenmeyer flask to prevent evaporation of the dichloromethane. Add 15 mL of fresh
dichloromethane to the separatory funnel (still containing the tea solution) and
repeat the extraction process. Again, allow the layers to separate and drain the
dichloromethane layer, including any emulsion layer, into the Erlenmeyer flask
containing the dichloromethane solution from the first extraction. Pour the tea
solution out of the top of the separatory funnel into a beaker.
Rinse the separatory funnel with water before pouring the combined
dichloromethane solutions into the funnel; add about 20mL of water. Stopper the
funnel, invert and rock it gently to mix the two layers. Some emulsion layer may be
present at this point. If only a thin layer of emulsion exists at the interface between
the aqueous phase and the dichloromethane solution, push a small piece of glass
wool to the bottom of the dichloromethane layer with a large stirring rod. The glass
wool will break the membranes of the emulsion. Drain the lower dichloromethane
layer slowly into a clean, dry 50-mL Erlenmeyer flask.
Add anhydrous magnesium sulfate to the dichloromethane solution. Cork the
flask and allow the mixture to stand for at least 10 min, swirling the flask
occasionally.
Weigh (tare) a dry 50-mL Erlenmeyer flask on a balance that measures to
0.001 g. Place a fluted filter paper in a dry conical funnel and filter the drying agent
from the dichloromethane solution collecting the filtrate in a tared 50 mL Erlenmeyer
flask. Rinse the magnesium sulfate remaining in the flask with approximately 2 mL of
dichloromethane and also pour this rinse through the funnel. Add a boiling stick or
boiling chip to the flask containing the dichloromethane solution so that it boils
without bumping
Evaporate the dichloromethane on a steam bath or water bath heated on a
hot plate in a hood. Alternatively, the dichloromethane may be removed by
evaporation, using a stream of nitrogen, in a hood, or with a rotary evaporator.
Continue the evaporation until a dry greenish residue of crude caffeine forms on the
bottom of the flask. Weigh the flask and determine the mass of crude caffeine.
Calculate the percent recovery. Cork the flask and store it in your laboratory drawer
for purification and analysis.
Cleanup:
Place the tea leaves in the non-hazardous solid waste container. Wash the
tea solution remaining from the initial extractions and the water remaining in the 125mL separatory funnel down the sink. Allow the flask containing the magnesium
sulfate drying agent to dry in a hood before putting the spent drying agent in the
inorganic waste container.
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