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Organic natural
products
Examples of useful organic
natural products include aspirin,
caffeine, morphine and quinine
Adjustments to the LC Chemistry Syllabus
In section 7.4 of the syllabus (Organic
Natural Products), the steam distillation of
an organic substance is being adjusted to
specify the extraction of clove oil and to
include the liquid-liquid extraction of
eugenol from the emulsion produced using
cyclohexane. This does not introduce any
new theory. The extension of this experiment
will make up for the reductions in the
mandatory experiments in sections 7.3 and
8.2.
Extraction techniques
• Steam distillation (extraction of
clove oil from cloves
• Solvent extraction (using an
organic solvent to extract a
natural product from an
aqueous solution)
 Cloves are the dried buds of a tree that is cultivated primarily in
Zanzibar and Madagascar. The tree produces abundant clusters
of small red flower buds that are gathered before opening and
are dried to produce the dark-brown, nail-shaped spice clove.
 Whole and ground cloves are popular food seasonings and
account for the use of half the world production of cloves. The
other half is ground and used in the manufacture of a type of
cigarette popular in Indonesia.
 Almost 20 percent of the clove's weight is essential oil, obtained
by distillation and used in perfumes, blends of spices,
medicines, and sweets. Clove oil is a powerful antiseptic, and is
also used as a local anaesthetic for toothache.
Why Steam Distillation?
•Steam distillation used because plant material
and oils would decompose if heated directly in a
simple distillation apparatus.
•Passing steam through the cloves avoids a very
high temperature that would destroy the plant
material. In the steam distillation of cloves, an
emulsion is formed. This emulsion consists of
droplets of oil of cloves dispersed with water.
Steam distillation
•Have a safety opening to the atmosphere
•Some organic compounds are immiscible with
water. Usually these compounds have a low vapour
pressure. After mixing them with water, however,
the mixture will distil when the sum of the two
vapour pressures reaches atmospheric pressure. It
follows, then, that this must happen below the
boiling point of water.
This process is known as steam distillation.
•Cover cloves with a little warm water (about 5
cm3).
•Use anti-bumping granules in the steam generator.
•If the level of the boiling water in the steam
generator falls too low, the system will not work
smoothly. Refill with hot water. Reconnect
everything and heat again.
•After 30 minutes disconnect steam generator to
avoid suck-back then turn off the heat.
•Collect 40 - 50 cm3 of the pale milky distillate
[emulsion]. Note the smell
•Oil separated by dissolving in solvent, placing in
separating funnel
•Collect organic solvent fraction and then evaporate
solvent.
Expt 23B
‘To isolate clove oil (eugenol)
from an emulsion of clove oil
and water by solvent
extraction (liquid-liquid)
using cyclohexane’
Solvent extraction involves adding an
organic solvent (e.g.cyclohexane) to the
clove oil emulsion. The cyclohexane
dissolves the oil of cloves in the
emulsion but does not mix with the
water. The organic solution (containing
cyclohexane and dissolved oil of cloves)
is then separated from the water using a
separating funnel, The organic solvent is
then allowed to evaporate leaving the
pure oil behind.
•Disconnect the dropping funnel from the rest of the
apparatus.
•Add about 10 cm3 of cyclohexane to the distillate
(about 50cm3 of the clove oil emulsion) in the
dropping funnel. Note that the cyclohexane floats on
the emulsion as it is less dense than water.
Stopper the dropping funnel and shake the mixture
back and forth about 10 times. Release any
pressure build-up carefully after each shake by
inverting the dropping funnel while holding the
stopper and slowly opening and shutting the tap.
This stage is referred to as ‘washing’ the emulsion
with organic solvent.
•Clamp the separating funnel containing the
mixture in the retort stand. Run the lower aqueous
layer off. Collect in beaker marked ‘aqueous layer’
• Collect the top layer - this contains the clove oil
and the cyclohexane. Label another beaker
‘organic layer’ and allow the organic layer to flow
into it.
•Pour the aqueous layer back into the separating
funnel. Add a fresh 10 cm3 of cyclohexane and
repeat the washing process two more times This
extracts the maximum amount of oil from the
emulsion.
Allow the organic layer to flow into the conical flask
containing the organic layers from the three washings. This
conical flask now contains about 30cm3 of cyclohexane
containing the oil of cloves dissolved in it plus some water
that has come out of the separating funnel when the
cyclohexane was being transferred from the separating
funnel. This water must now be removed.
Using a spatula add anhydrous magnesium sulfate in small
quantities to the cyclohexane solution in the conical flask
and swirl after each addition.
You will notice that at first MgSO4 will form clumps that stick
to the sides and bottom of the flask where it comes in
contact with the water present in the flask. Continue adding
MgSO4 until the fine powder settles at the bottom of the
flask without forming clumps. Don’t worry about adding too
much as this will be filtered off later.
Obtain a clean dry conical flask and find its mass.
The hydrated MgSO4 must now be removed. Place a fluted filter
paper in a clean dry funnel above the conical flask you have
just weighed.
Pour the contents of the conical flask containing the oil of
cloves, the cyclohexane and magnesium sulfate into the fluted
filter paper and allow the clear cyclohexane containing the oil of
cloves to flow through the filter paper and into the weighed
conical flask.
Using 10cm3 of fresh cyclohexane
Solvent, wash out the conical flask
containing the magnesium sulfate
residue and traces of oil into the fluted filter paper. This
removes any traces of oil that
may be attached to the
magnesium sulfate
in the conical flask.
In a fume hood, place the conical flask containing the
oil of cloves solution on a water bath and evaporate
off the volatile cyclohexane solvent (Cyclohexane has
a b.p. Pg 810). Do not heat the conical flask directly
with a hotplate as this could boil off the clove oil as
well as the cyclohexane. Cyclohexane is also
flammable.
Note that a small quantity of an oily substance is left
in the conical flask. This oily substance is the oil of
cloves which contains mainly eugenol as the
essential ingredient but some other oils are also
present. Note the smell of the clove oil. Do not allow
the clove oil to come in contact with your skin.
Allow the conical flask to stand overnight.
Record the new mass of the conical flask and
calculate the mass of oil formed
Questions on this experiment
1. Write a brief note to explain how steam distillation is used to extract
oils from plant materials.
When steam is passed through the plant material, it forms a gaseous
emulsion with the oil in theplant material. This very hot emulsion is forced
under pressure into a Liegbig condenser whichconverts the gaseous
emulsion into a liquid. The oil may then be extracted from the emulsion
using an organic solvent.
2. Why is it not possible to distil the clove oil directly from the cloves?
If the cloves were heated directly, the heat would cause them to char and
the oil would be destroyed. Steam is used as the temperature is kept slightly
above 1000 C and at this temperature the clove oil is not destroyed.
3. Why is the product of this experiment referred to as an emulsion?
Name one other common emulsion found in everyday life.
An emulsion is formed when droplets of oil are dispersed in a liquid like
water. Many paints are sold in the form of emulsions. Mayonnaise is also an
emulsion of oil in water.
4. In carrying out this experiment a long glass tube open at both ends
is usually placed in thesteam generator. What is the reason for this?
The long glass tube is a safety tube and is used to ensure that there is not a
build up of pressure inthe steam generator. As the pressure increases inside
the steam generator, water is pushed up the safety tube.
5. What is the purpose of the steam trap in the experiment?
As the name suggests, the steam trap collects or traps steam that has
condensed to water. If the trap were not present, the flask containing the cloves
would quickly fill up with water from the condensed steam.
6. Describe how you would isolate the clove oil from the distillate.
The clove oil can be isolated using a process called solvent extraction. This
involves adding an organic solvent to the emulsion. A suitable organic solvent is
petroleum ether or dichloromethane.
The emulsion and organic solvent will be added to a separating funnel and the
two liquids shaken for a few minutes in the stoppered funnel. The two liquids
separate into layers and the water layer is discarded. The organic solvent is
allowed to evaporate leaving the oil behind in the evaporating basin.
7. What name is given to the main constituent of the oil found in cloves?
Eugenol.
8. Why are cloves usually picked before they flower?
They are picked before they flower because this is the stage at which they are
richest in oil.
9. Give two uses for clove oil.
Clove oil is used for flavouring food products, in antiseptics, and in perfumes
and soaps.
10. Why is it better to use whole cloves rather than powdered cloves in
this experiment? Powdered cloves have usually lost a lot of their oil
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