Summer Research Program for Science Teachers
Bergen Academies
2000
Activity #2 Related to Natural Products
Activity 1: Operation of the Microwave Oven for Chemistry Experiments
Activity 3: Growing Barley and Detecting the Presence of Amino Acids
Introduction to Activity 2: Natural products are substances produced in living systems that may be useful to humankind, especially in the field of medicine. For example, taxol is a substance derived from Pacific yew trees that has been shown to be effective against certain types of cancer. The extraction of such substances is necessary before their therapeutic value can be evaluated.
This action plan presents three activities related to natural products. One of these is the extraction of a natural product, caffeine, from tea leaves. This has been chosen since the starting ingredients are relatively easy to come by, and the student will still find a reasonable level of challenge. The microwave oven was chosen to provide energy for heating the tea bags, to emphasize the importance of the microwave oven in the field of organic chemistry. Microwave-assisted chemical reactions are increasingly important, especially for organic chemistry. Many chemical reactions that used to take hours now take minutes or seconds with the use of microwave techniques. A simple demonstration of the microwave is included in the action plan. A third activity is the growing of barley under controlled conditions, since it is often necessary to grow plants (or animals) to provide raw material from which natural products can be extracted. The growing of plants offers ample opportunity for open-ended activities
II. Extraction of
Caffeine from Tea Leaves
Caffeine is a natural product found in coffee and tea.
It is chosen here because it is relatively easy to extract
compared to some of the other substances students might be
interested in.
Objective:
To obtain the greatest number of grams of
caffeine from four bags of tea.
[9-12 Content Standard E- Abilities of technological design]
Materials and Equipment
rotovapor machine or hot plate
three 400-mL beakers
1000-mL beaker
basin for ice
ice (cubes or crushed)
Earl Grey tea (or any tea containing caffeine)
petri dish
100-mL graduated cylinder
glass stirring rod
NaHCO3
500-mL separatory funnel
ring stand with ring
expendable rubber tubing
dichloromethane
regular funnel
hood
goggles
250-mL Erlenmeyer flask
filter paper
Na2SO4
(anhydrous)
rubber tubing
aspirator or vacuum setup
round-bottom flasks
gloves
organic waste can
kitchen mitts
stirring rod
[Teaching Standard D- Make accessible science tools]
Before conducting this experiment, ensure individuals
(such as wearers of pacemakers) who should not be near operating
microwave ovens are out of the room.
(Students perform this activity in groups of four or
five. Every member has a lab book in which procedures,
observations, and data must be recorded. The four members
of each group have specific tasks to do. Task #1 is safety
engineer, the person who directs the others and reminds them to
wear goggles and to follow other safety procedures, task #2 is
balance technician, task #3 is microwave oven technician, and
task #4 is “setups technician,” who sets up various
pieces of equipment, such as the separatory funnel. For
five-member groups, there is a director distinct from the safety
engineer. )
1. Put on goggles.
2. Set up the separatory funnel in advance. Place
the ring stand in the hood. It is desirable to place rubber
bumpers on the iron ring so as to protect the glass from
breakage. The rubber for this will come from expendable
rubber tubing. Cut a short section of tubing, then cut it
open lengthwise, so that it can be wrapped around the ring.
Place these bumpers approximately 120o from each other
on the iron ring, and this will protect the funnel against damage
when it is placed in the iron ring.
3. Prepare a basin of ice for cooling the beaker
of tea later.
4. In a hood start heating the water in the
rotovapor machine (or in a beaker on the hot plate, if there is
no rotovapor machine).
5. The objective is to produce the greatest number
of grams of caffeine per tea bag. Students are given this
objective in advance, so they can do research in the library, on
the Internet, and by talking to experts, to identify promising
teas for extraction of the most caffeine. [9-12 Content Standard A- Identify questions/concepts that guide
inquiry] Start with four tea bags.
6. Four tea bags are to be massed. It
is important that tea leaves not leave the bags, so the bags
should not be punctured, but strings and tags should be cut off
and paper wrappers removed before massing.
7. Using the graduated cylinder, measure 100mL of
distilled water into a 400-mL beaker.
8. Mass 2.0 g of NaHCO3 and use glass
rod to stir into beaker of water.
9. Submerge tea bags in the solution in the
beaker.
10. Place a clean, dry petri dish on the top of
the beaker to prevent splattering. Thus covered, the beaker
should be placed on the turntable of the microwave oven. Set
microwave oven for 100% power for a duration of 1 minute. Then
start the oven. After one minute, if boiling is observed,
then go to next step. If no boiling is observed, irradiate
for another 1-minute interval, and continue to do so in 1-minute
intervals until boiling is observed.
11. Decant the liquid to a 400-mL beaker and
examine the liquid to see if any tea leaves have escaped the
bags. If the liquid is free of tea leaves, then proceed to
the next step. Otherwise, repeat steps 6 through 11.
12. Cool the tea by setting the beaker in a basin
of ice.
13. Ensure separatory funnel valve shut. Using
an ordinary funnel, pour the tea into the separatory funnel.
14. Put on gloves.
15. The separatory funnel should be placed in the
hood if it has not been already.
16. Using a graduated cylinder, measure 25 mL of
dichloromethane. Dichloromethane and the tea mixture can
form an emulsion difficult to separate if allowed to be agitated,
so slowly pour the dichloromethane into the
separatory funnel.
17. Avoid shaking the separatory funnel too
vigorously. Remove the top of the separatory funnel (if it
is not already removed), and gently tilt the mixture
back and forth, or else a bothersome emulsion will form.
18. After the bottom layer is removed from the
separatory funnel, it must pass through a drying agent (such as
Na2SO4). The purpose of this second
filtration setup is to remove any H2O from the bottom
layer. Set up the Erlenmeyer flask close by the separatory
funnel, and place a conical funnel in the Erlenmeyer flask.
Line the conical funnel with filter paper. Place a small
amount of dichloromethane on the filter paper so that it will
adhere to the sides of the funnel. This setup will be used
in the next step to remove Na2SO4.
19. Place an Erlenmeyer flask under the separatory
funnel to catch the bottom layer. Gently open the valve to
allow only the bottom layer to pass through. Turn the valve
to the shut position before any of the top layer passes through.
Add anhydrous Na2SO4 to the liquid and
stir. Pour the contents of this flask through the
paper-lined conical funnel so as to remove the Na2SO4.
20. Set up the rotovapor machine. [9-12 Content Standard E- Understandings about science and
technology] (Omit this step if you will be
using a hot plate instead.) Ensure tubing is hooked up for
aspirator (or vacuum) and for cooling water, including a secure
hose leading to a drain. Turn on the cooling water.
Transfer the filtrate to a round-bottom flask, and
attach this to the appropriate end of the rotovapor machine.
Ensure a receiving flask is also in place. Apply a partial
vacuum by opening the vacuum valve, or, if you lack a vacuum
valve, set up an aspirator to provide a partial vacuum. Shut
the valve at the top of the condenser. Start the rotation
of the sample flask. Gently lower the sample flask into the
water, but if the solvent boils too violently, elevate the sample
flask and lower the temperature of the water, then try again.
21. If you lack a rotovapor machine, do the
following: set up a heating bath in a 1000-mL beaker on a
hot plate in the hood. Place the filtrate in an Erlenmeyer
flask, and using kitchen mitts, lower the Erlenmeyer flask until
its bottom is in contact with the hot water. This will provide
heat to evaporate the solvent. Any time the filtrate begins
to boil, lift the flask, then lower it again. Eventually
the solvent will be driven off and a solid will be left behind.
22. With a spatula, remove the solid left behind
and mass it. This solid is principally caffeine. Record
this for comparison with other teas.
23. If this is the last tea sample to be tested,
then commence clean up.
Repeat the experiment with other brands of tea to see which is has the most caffeine per bag. The number of tea bags tested at a time may also be changed. [Content Standard Unifying Concepts- Change, constancy, and measurement]