Essential Oils: Extraction of Oil of Cloves by Steam Distillation

Isolation of (R )-(+)-Limonene from Orange Peel

Adapted from Pavia.

Essential oils are volatile compounds responsible for the aromas commonly associated

with many plants (see essay “Terpenes and Phenylpropanoids”). The chief constituent

of the essential oil from cloves is aromatic and volatile with steam. In this experiment,

you will isolate the main component derived from this spice by steam distillation. Steam

distillation provides a means of isolating natural products, such as essential oils, without

the risk of decomposing them thermally.

▲found in oranges found in spruce trees▲

Apparatus

Using a 20- or 25-mL round-bottom flask to distill and a 10-mL round-bottom flask to

collect, assemble a distillation apparatus similar to that shown in Figure 1. Use a hot

water bath to heat and insert a water condenser. The collection flask may be immersed

in ice to ensure condensation of the distillate. Be careful not to assemble the apparatus

permanently because you will have to open it to add the spice and prepare the

distillation mixture.

▲Figure1. Steam distillation apparatus

Preparing the Orange

Weigh approximately 1.0 g of your orange peel onto a piece of weighing paper and

record the exact weight. Mix the orange peel with 12–15 mL of water in the 20-mL

round-bottom flask and add a magnetic stirring bar or boiling stone. The solution will

begin to foam. Be careful not to let the foaming action become vigorous enough to

rise above the level of the neck of the round-bottom flask. As the solution begins to

foam, reduce the vacuum so that the bubbles recede into the flask. Repeat this

process until foaming action subsides or until 15 minutes have passed, whichever is

longer.

Steam Distillation

Turn on the cooling water in the condenser, begin stirring if you are using a stirring bar,

and begin heating the mixture to provide a steady rate of distillation. If you approach

the boiling point too quickly, you may have difficulty with frothing or bump-over. You

will need to find the amount of heating that provides a steady rate of distillation but

avoids frothing or bumping. A good rate of distillation would be to have 1 drop of liquid

collected every 2–5 seconds. Continue distillation until at least 5 mL of distillate has

been collected. Normally, in a steam distillation the distillate will be somewhat cloudy

due to separation of the essential oil as the vapors cool. However, you may not notice

this and still obtain satisfactory results.

Extraction of the Essential Oil

Transfer the distillate to a 15-mL screw-cap centrifuge tube and add 1.0 mL of

acetone/pet ether to extract the distillate. Cap the tube securely and shake it

vigorously, venting frequently. Allow the layers to separate. If the layers do not separate

well, the mixture may be spun in a centrifuge. Stirring gently with a spatula sometimes

helps resolve an emulsion. It may also help to add about 1 mL of a saturated sodium

chloride solution. For the following directions, however, be aware that the saturated salt

solution is quite dense, and the aqueous layer may change places with the organic

layer, which is normally on the bottom. Transfer the lower methylene chloride layer to a

clean, dry, 5-mL conical vial. Repeat this extraction procedure two more times with

fresh 1.0-mL portions of organic solvent and place them in the same 5-mL conical vial

as you placed the first extraction. If there are visible drops of water, you need to transfer

the organic solvent solution to a clean, dry, 5-mL conical vial.

Drying

Dry the organic solution by adding granular anhydrous sodium sulfate to the conical

vial or small beaker. Let the solution stand for 10–15 minutes and stir occasionally.

Evaporation While the organic solution is being dried, clean and dry the first 5-mL

beaker and weigh (tare) it accurately. Be careful to keep any of the sodium sulfate

from being transferred. Working in a hood, evaporate the organic solvent from the

solution by using a gentle heating.

Pre-Laboratory Questions

1. Why was a steam distillation rather than a simple distillation performed in the

isolation of limonene from orange peel?

2. What type of product is expected from the reaction of limonene with Br2/CH2Cl2?

With chromic acid?

3. Explain why the substitution of 1-propanol, bp 97 °C (760 torr), for water in a

steam distillation would not work.

4. Suppose that you are to steam-distill a sample of a natural product whose vapor

pressure at 100 °C is known to be half that of limonene. What consequence

would this have on the amount of distillate required per mole of the natural

product present?