THE EXTRACTION OF CAFFEINE FROM COFFEE

Caffeine From Coffee
THE EXTRACTION OF CAFFEINE FROM COFFEE
PURPOSE
• To carry out an extraction of an aqueous solution of coffee
with an organic solution.
• To isolate caffeine from
coffee.
MATERIALS NEEDED
• To determine the melting
point of caffeine.
• 100 mL coffee extract solution
• 2 g solid sodium carbonate
• 25 mL methylene chloride
DISCUSSION
• spoonful anhydrous sodium sulfate
• 250 mL beaker
Every day, throughout the
• 500 mL Erlenmeyer flask
world, people start out their
• 12.5 cm filter paper
morning by extracting a
• iron ring
• glass funnel
family of natural products
• 50 mL beaker
called alkaloids from
• pipet
naturally occurring materials
• hot plate
and then drinking this
• melting point apparatus
extract. The most common of
• melting point tube
• test tube
these alkaloids caffeine,
1,3,7 – trimethylxanthine,
occurs naturally in coffee
beans and tea leaves, but is added to soft drinks and stimulants
such as Vivarin and No-Doz, dieting aids such as Dexatrim and
Diatac and painkillers such as Anacin and Excedrin.
Alkaloids are a broad category of nitrogen containing organic
metabolites produced by plants. Since they contain nitrogen,
they behave like bases (alkalis) and hence, they are termed
alkaloids. Other common alkaloids are morphine, quinine, cocaine
and codeine. These substances are extremely bitter and/or toxic.
By producing them, plants make their leaves unattractive to
eating by insects and higher animals.
In this experiment, you will extract caffeine from coffee using
methylene chloride (CH Cl ). Methylene chloride is an organic
2
2
solvent that is somewhat nonpolar. In this experiment, we take
advantage of the same principles we used in thin layer
chromatography, especially “like dissolves like”. Methylene
chloride is a liquid but it isn’t like water so they form two
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Caffeine From Coffee
layers, just like vinegar and oil. The caffeine molecule is
closer in structure to methylene chloride, so it will dissolve
in that layer. The two layers can then be separated, and the
methylene chloride, which has a very low boiling point, can be
evaporated in the hood, leaving a residue of caffeine.
In order to verify that you have obtained caffeine, you will
take a melting point of this residue. Melting points are a
unique property of pure substances. For example, pure water
melts at 0 degrees C. Pure caffeine melts at 238 ° C. If the
material you collect melts at a temperature close to 238
degrees, you can be more confident that it is caffeine. The
material that you have extracted will probably have a slightly
lower melting point.
PROCEDURE
A .
Extraction of the Coffee Solution
1.
To a clean 500 mL Erlenmeyer flask, add 100 mL of coffee
extract. This extract will have been prepared for you in
advance.
2.
Add approximately two grams of sodium carbonate (NaCO ) to
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the coffee solution. This will react with some of the
substances in the coffee extract and make them extremely
water soluble. Swirl the mixture until all the sodium
carbonate dissolves.
3.
Add 25 mL of methylene chloride (CH Cl ), and vigorously
2
2
swirl the mixture for 10 minutes. Do not shake the mixture
or an emulsion will form.
4.
Allow the mixture to stand and separate into two layers; a
dark aqueous top layer and a clear methylene chloride
bottom layer.
5.
Carefully pour off into a beaker, as much of the top layer
as you can, without removing the bottom layer. This process
is called decanting.
6.
Place a 12.5 cm fluted filter paper in a long stem glass
funnel. Put the funnel in a small iron ring and suspend it
over a 250 mL Erlenmeyer flask.
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Caffeine From Coffee
7.
Using a squeeze bottle of water, thoroughly wet the filter
paper.
8.
Slowly and carefully pour the methylene chloride/water
mixture into the fluted filter paper. The excess water will
drain through and the methylene chloride solution of
caffeine will remain on the filter paper.
9.
Using a pipet, transfer the methylene chloride solution to
a 50 mL Erlenmeyer flask. To this solution, add a scoop of
anhydrous sodium sulfate (Na SO ), in order to remove the
2
4
last traces of water.
10.
While the solution is drying, weigh (tare) a 50 mL beaker
to the nearest 0.001 g on a balance. Record this tare
weight in Table 1 on the DATA SHEET.
11.
Using a pipet, transfer the dried solution to the tared 50
mL beaker.
12.
Evaporate most of the methylene chloride in the hood on a
warm hot plate. When only a fraction of a milliliter of
liquid is left, remove the beaker from the hot plate. Allow
the beaker to stand in the hood for a minute or two. The
heat remaining in the glass will cause the last amount of
methylene chloride to evaporate and produce a solid residue
of crude caffeine.
13.
In order to determine your recovery of caffeine, reweigh
the cool beaker and record this mass in the Table.
14.
By difference, determine the mass of the caffeine in the
beaker and record this value in the Table.
15.
Pure caffeine is a white solid. Describe the appearance of
your product in the Table.
B .
Melting Point Determination
1.
To a melting point tube, add a small amount of your
caffeine. This can most easily be done by pressing the open
end of the tube down on the caffeine, turning the tube
right-side-up and tapping the tube on the bench until the
solid falls to the bottom of the tube. Tap the tube on the
bench a few more times so that the caffeine is compacted.
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Caffeine From Coffee
2.
Place the tube in the slot of the melting point apparatus.
Turn on the switch of the instrument. This will turn on a
light that illuminates the sample. By looking through the
magnifying glass, you should have a clear view of your
sample.
3.
Turn the heating dial to a setting of about 40. This will
cause a rapid heating of your sample initially, but should
not cause it to melt. As the temperature increases, there
will be a decrease in the rate of heating. Since your
sample will melt above 200 ° C, you may need to periodically
increase the setting of the heating dial. Ideally, the
temperature increase at the melting point should be only 1-
2 ° C per minute.
4.
Record the range of the melting range of your sample as
follows. In the Table record the temperature at which you
first see liquid beginning to form. The sample will
continue to melt. When the last of the sample has melted,
record the second temperature. These two values are
separated by a dash, i.e., 63-65 ° C. For a relatively pure
compound, this temperature range will generally be only a
few degrees.
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Caffeine From Coffee
DATA SHEET - THE EXTRACTION OF CAFFEINE FROM COFFEE
Tare weight of the empty beaker (g)
_____________
Mass of the beaker and the caffeine (g)
_____________
Mass of the caffeine (g)
_____________
Appearance of the caffeine
Melting range of the caffeine
QUESTIONS
1.
a. Is methylene chloride more or less dense than water?
b. What evidence do you have to support your answer?
2.
Was your melting point the same as the reported melting
point? If not, why not?
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Caffeine From Coffee
3.
Why was sodium carbonate added to the coffee solution?
4.
Explain why the caffeine that you obtained in this
experiment may not have been white in color.
5.
List some substances that contain caffeine other than
coffee.
a.
b.
c.
d.
e.
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