Chemistry Experiment (Module: Lab Technique Training)
IJSO Training: Chemistry Experiment
Lab Technique Training: Separating an Organic Mixture and Analyze a Mixture by
TLC
Isolation of the Active Ingredient in an Analgesic Drug
Introduction:
The purpose of this experiment is to illustrate the laboratory techniques that
are often applied for separating the components in an organic mixture. The major
ingredients that present in the common painkilling drugs are aspirin, acetaminophen,
and caffeine:
O
O
OH
O
HN
CH3
H 3C
O
CH3
O
OH
Aspirin
(Acetylsalicylic acid)
mp 135°C
Acetaminophen
(p-Hydroxyacetanilide)
mp 169-170.5°C
O
CH 3
N
N
N
N
CH 3
Caffeine
mp 238°C
In this activity, you will be given a powdered sample of a common pain-killer
that contains all of the three above ingredients. You will try to isolate the three
different ingredients from the sample mixture by making use of their different
solubility in different solvents.
Aspirin has two functional groups attached to the aromatic ring: an ester group
and a carboxylic acid group. It is an acidic compound and dissolves in basic solutions
(in which aspirin is converted into a water-soluble salt) but not in neutral or acidic
aqueous solutions.
It is also soluble in some organic solvents such as
dichloromethane (CH2Cl2).
On the other hand, acetaminophen is a phenol with an acetamido group
attached to the aromatic ring. It is a very weak acid and dissolves in strongly alkaline
solutions but not in mildly basic, neutral, or acidic aqueous solutions. In addition, it is
insoluble in dichloromethane.
Contrary to the above two compounds, caffeine is polar and soluble in
aqueous solutions. Being a base (with a lone pair available at one of the nitrogen
atoms), it is highly soluble in strong acids because caffeine can be protonated and
converted to a water-soluble salt. Like aspirin, caffeine is also soluble in
dichloromethane.
They can be easily separated by making use of their different solubility in
different solvents. For example, aspirin and caffeine are soluble in dichloromethane
while acetaminophen does not. Hence, we can separate acetaminophen from aspirin
and caffeine with dichloromethane followed by filtration.
Chemistry Experiment (Module: Lab Technique Training)
Notes:
(i)
Aqueous solution and dichloromethane are immiscible. The latter is denser
than the former.
(ii)
Rotary evaporator can help to evaporate the solvent from an organic solution
efficiently.
Procedure:
1.
Separation of acetaminophen/binder from aspirin caffeine
(Retain about 0.05 g of the sample powder for TLC analysis)
Weigh the drug powder and put it into a 25-mL conical flask. Add about 10 ml
of dichloromethane. Warm the mixture briefly with a ~30oC water bath, and stir the
mixture for 2 to 3 minutes. Filter the mixture with a pre-weighed filter paper and use
a test tube to collect the filtrate. Wash the solid with 1 to 2 ml of dichloromethane.
Keep the solid residue.
2.
Separation of aspirin and caffeine
Transfer the filtrate to a separatory funnel and add about 8 ml of ~3 M NaOH
solution. Shake the funnel and let the funnel stand to allow the two phases to separate.
Transfer the upper phase into a conical flask. Add another 5 ml of ~3M NaOH
solution into the funnel and extract the organic layer again. Combined the aqueous
solutons.
3.
Isolation of aspirin
Acidify the alkaline solution (which contains aspirin) that collected in Part (2)
with 3 M hydrochloric acid until the pH of the solution reached about 3. Put the flask
into an ice bath. Filter the mixture with a pre-weighed filter paper. Wash the solid
with 1 to 2 ml of iced-water. Allow the solid to dry in air. Weigh the filter paper
which contains aspirin and determine the mass of the solid obtained.
4.
Isolation of acetaminophen
Transfer the solid residue obtained in Part (1) to a conical flask, and add 8 mL
of ethanol. Heat the mixture to gentle boiling for 1-2 minutes. Filter the mixture into
a beaker. Evaporate the solvent carefully, and the solid residue obtained is the
isolated acetaminophen. Weigh the solid obtained.
5.
Isolation of caffeine
To the dichloromethane solution (which contains caffeine) obtained in Part (2),
add a small amount of anhydrous MgSO4 powder (to dry the solution). Swirl the
mixture for 1 to 2 minutes to complete the drying process. Filter the mixture and
collect the filtrate with a pre-weighed round-bottom flask. Wash the residue on the
filter paper with a small amount of dichloromethane, and combine the washing with
the filtrate. Evaporate the solvent from the filtrate with a rotary evaporator (or by
Chemistry Experiment (Module: Lab Technique Training)
simple distillation). Weigh the round-bottom flask to determine the mass of the
solid obtained.
Data:
1.
Mass of the given drug sample:
2.
Mass of acetaminophen isolated:
3.
Percentage of acetaminophen present in the sample (experimental):
4.
Mass of caffeine isolated:
5.
Percentage of caffeine present in the sample (experimental):
6.
Mass of aspirin isolated:
7.
Percentage of aspirin present in the sample (experimenta0:
Chemistry Experiment (Module: Lab Technique Training)
8.
The powdered sample that is given to you is actually contains several crushed
tablets of different brands that are mixed together. (Ask your teacher) The
actual compositions of the sample:
Brand
No. of tablets
Component 1
Component 2
9.
Look up the ingredient information from the packages of the drugs and
calculate the theoretical mass and percentage of each of the individual
ingredient that supposedly present the given crushed sample. Compare the
theoretical and experimental determined contents of the active ingredients in
the sample.
Total mass of the tablets: (theoretical)
(experimental)
Ingredients
Mass (theoretical) Percentage
(theoretical)
Percentage
(experimental)
Acetaminophen:
Caffeine:
Aspirin:
9.
Are your experimentally determined data greatly differed from the theoretical
ones? Why?
Chemistry Experiment (Module: Lab Technique Training)
Analysis the components of common drugs by TLC
(Thin-Layer Chromatography)
Procedure
1.
Prepare solutions for the given standard samples:
(a)
Aspirin – dissolve about 0.1 g of aspirin in 3 mL of methanol in a vial.
(b)
Caffeine – dissolve about 0.05 g of caffeine in 3 mL of methanol in a
vial.
(c)
Acetaminophen – dissolve about 0.05 g of acetaminophen in 3 mL of
methanol in a vial.
2.
Prepare solutions for the aspirin, caffeine and acetaminophen isolated from the
given powdered drug sample:
(d)
Aspirin – dissolve about 0.1 g of the isolated aspirin in 3 mL of
methanol in a vial.
(e)
Caffeine – dissolve about 0.05 g of the isolated caffeine in 3 mL of
methanol in a vial.
(f)
Acetaminophen – dissolve about 0.05 g of the isolated acetaminophen
in 3 mL of methanol in a vial.
(g)
Original mixture – dissolve about 0.05 g of the original powdered drug
mixture in 3 mL of methanol in a vial.
(Make sure the samples solutions are labeled properly)
Selection of solvent for development:
Spot the solutions of standards on TLC plates (at different positions) and run
the TLC with different solvents for development given. [The solvents for
development are usually mixtures of organic solvents for running TLC and are
not the same as the solvent used in dissolving the solutes in Step (1) above.
Also, the TLC plates are not reusable. Use one spotted TLC plate for each
solvent system.] Compare the results and choose the best solvent for the
following part.
Three solvent systems will be given for testing the standard solutions. They
are (i) n-hexane, (ii) ethanol and (iii) butyl acetate/acetic acid (4:1) mixture.
3.
Obtain a TLC plate and have the white colour side facing up.
4.
Use a pencil and a ruler to draw a starting line at about 5mm from the bottom
of the plate.
5.
Apply the solutions one by one along the line using capillary tubes.
6.
Add a small amount of n-hexane to a glass jar. Make sure that the solvent
level is below the line drawn (the sample spots) on the plate.
Chemistry Experiment (Module: Lab Technique Training)
7.
Develop the TLC plate by putting it vertically inside the glass jar and cover
the jar immediately. Wait for the solvent to advance up the plate. Remove the
plate from the jar when the solvent front reaches the top of the plate.
8.
Repeat the above steps using the other two solvents ((ii) ethanol; (iii) butyl
acetate/acetic acid (4:1)).
All of the standard and sample solutions are colourless and therefore the spots
cannot be directly seen on the TLC plates. However, you can use an
ultraviolet lamp to visualize the spots on the plates. Mark out the shapes of the
spots on the plate using a pencil. Find out the solvent that gives the best
separation for the three standard compounds. Use the chosen solvent system
for analysing the sample solutions.
TLC
run
#1
#2
#3
#4
Spots
Std. Ac
Std. Ac
Std. Ac
Std. Ac
Std. As
Std. As
Std. As
Std. As
Std. Ca
Std. Ca
Std. Ca
Std. Ca
#5
Std. Ac
Std. As
Std. Ca
#6
Std. Ac
Std. As
Std. Ca
#7
Std. Ac
Std. As
Std. Ca
Std. Ac = Standard acetaminophen (given)
Std. As = Standard aspirin (given)
Std. Ca = Standard caffeine (given)
Solvent (A):
Solvent (B):
Solvent (C):
n-Hexane
Ethanol
Butyl acetate / acetic acid (4:1)
The best solvent for running the TLC
is:
---------Product
obtained in
part (3)
Product
obtained in
part (4)
Product
obtained in
part (5)
Original
mixture
Solvent
for
development
Solvent (A)
Solvent (B)
Solvent (C)
The selected
one
The selected
one
The selected
one
The selected
one
Chemistry Experiment (Module: Lab Technique Training)
9.
.
Stick the developed TLC plates onto spaces provided below:
Run 1
Run 2
Run 3
Solvent: n-hexane
Solvent: ethanol
Solvent:
butyl acetate / acetic
acid (4:1)
Run 4
Run 5
Run 6
Run 7
Product obtained
in part (3)
Product obtained
in part (4)
Product obtained
in part (5)
Original mixture