Essential Oils: Extraction of Oil of Cloves by Steam Distillation

Essential Oils: Extraction of Oil of Cloves by Steam Distillation

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. Identification and characterization of

this essential oil will be accomplished by infrared spectroscopy. Oil of cloves (from

Eugenia caryophyllata) is rich in eugenol (4-allyl-2- methoxy- phenol). Caryophyllene is

present in small amounts, along with other terpenes. Eugenol (bp 250°C) is a phenol, or

an aromatic hydroxy compound

Setting Up

Assemble a steam distillation apparatus, as shown in Isolation of Trimyristin from Nutmeg.

Be sure to include the water condenser.

Use a 20- or 25-mL round-bottom flask as a distillation flask and water bath to heat the

distillation flask. Weigh approximately 1.0 g of ground cloves or clove buds onto a

weighing paper and record the exact weight. If your spice is already ground, you may

proceed without grinding it; if you use clove buds, cut the buds into small pieces. Mix

the spice with 12–15 mL of water in the round-bottom distillation flask, add a magnetic

stirring bar, and attach the flask to the distillation apparatus. Allow the spice to soak in

the water for about 15 minutes before beginning the heating. Be sure that all the spice

is thoroughly wetted. Swirl the flask gently, if needed.

Steam Distillation Apparatus▲

Extraction and Isolation

Steam Distillation Turn on the cooling water in the condenser, begin stirring the mixture

in the distillation flask, and begin heating the mixture to provide a steady rate of

distillation. The temperature for the heating device should be about 130°C. If you

approach the boiling point too quickly, you may have difficulty with frothing or bump-

over. You 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 one drop

of liquid collected every 2–5 seconds.

Normally in a steam distillation, the distillate is somewhat cloudy owing to separation of

the essential oil as the vapors cool. You may not notice this, but you will still obtain

satisfactory results.

Extraction of the Essential Oil

Collect all the distillate in a small beaker. Using a calibrated Pasteur pipette (see

instructor), add 2.0 mL of acetone to extract the distillate.

Allow the layers to separate. Using a Pasteur pipette, transfer the organic layer to a

clean, dry, beaker. Repeat this extraction procedure two more times with fresh 1.0-mL

portions of organic and combine all the organic extracts in the same beaker that you

used for the first extraction.

Drying

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

beaker. Transfer the supernatant liquid to a clean, dry beaker and prepare to

evaporate the solvent.

Your product is a volatile oil (i.e., a liquid), and if you continue to heat and evaporate

the liquid beyond the point where the solvent has been removed, you will likely lose

your sample.

Analysis

Weigh the trimyristin and determine its melting point. The reported melting point is 55–56

°C. Based on the original weight of nutmeg used, calculate the percent recovery.

Calculations:

Mass Recovered

% Recovery = ---------------------

Original Mass

Pre-Laboratory Questions

1. Why is eugenol steam-distilled rather than purified by simple distillation?

2. A natural product (MW = 150) distills with steam at a boiling temperature of 99°C

at atmospheric pressure. The vapor pressure of water at 99°C is 733 mm Hg.

a. Calculate the weight of the natural product that codistills with each gram of

water at 99°C.

b. How much water must be removed by steam distillation to recover this natural

product from 0.5 g of a spice that contains 10% of the desired substance?

3. In a steam distillation, the amount of water actually distilled is usually greater

than the amount calculated, assuming that both water and organic substance

exert the same vapor pressure when they are mixed that they exert when each is

pure. Why does one recover more water in the steam distillation than was

calculated? (Hint: Are the organic compound and water truly immiscible?)