Steam Distillation to Extract Essential Oils Lab Report

Experiment Extracting Essential oil via steam distillation

In this experiment, students isolated the natural product limonene from orange peel using steam distillation.

Introduction

Steam distillation allows for the separation and purification of organic compounds that are immiscible with water. Steam distillation provides for the ability to distill a compound at just below 100 °C even when the boiling point of the pure organic compound is far above 100 °C (the boiling point of limonene is 176 °C). This can be of tremendous value in the purification of substances that are heat sensitive and would therefore decompose at higher temperatures (citral is a chemically labile substance).

How does it work? The laws of physics completely change for immiscible compounds. Each component will exert its own vapor pressure, independent of the other components present and independent of the mole fraction. As a result, the mixture will boil at a temperature lower than the boiling point of either component as a pure compound, i.e. lower than the boiling point of the most volatile component, lower than 100 °C.

For the steam distillation, the vapor pressure is the sum of the vapor pressures of the pure component(s) and water, at a given temperature. The mole fractions do not matter.

 

P Total = P°A + P°H2O = 1 atm = 760 mm Hg

 

Because water has a much lower boiling point compared to limonene, its vapor pressure at a specific temperature will be much larger, relatively speaking. For example, at 99 °C, the vapor pressure of water is 733 mm Hg. As a result, limonene will distill despite its low vapor pressure at that temperature. This is because it will only need a vapor pressure of 27 mm Hg at 99 °C to distill. The mixture will distill when the sum of the vapor pressures equals atmospheric pressure. Separation of the two liquids will be easy because limonene is immiscible in water. We will utilize a special piece of laboratory equipment, called a Separatory funnel, for this purpose.

 

The name Limonene is derived from lemon. In particular, the rind of lemons, as well as other citrus fruits, contains considerable amounts of limonene which contributes to their odor. Limonene is a chiral molecule (see structure below), and biological sources produce only one of the two possible enantiomers: D-limonene ((+)-limonene), which is the (R)-enantiomer.

 

 

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Steam Distillation Apparatus:

 

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Watch the video on how to extract the essential oil Limonene from lemon https://www.youtube.com/watch?v=IC0qYhQ2XNg, then answer the following questions.

 

  1. What was the mass of lemon peel shavings to begin the distillation?
  2. How does the condenser work?
  3. What is in the vapor/distillate?
  4. If there are two phases are the components miscible or immiscible?
  5. Why does the distillate appear cloudy?
  6. Referring to the written discussion above, approximately what percentage of the distillate do you expect to be the limonene? (Rough educated guess)
  7. Of the two phases in the distillate (water and limonene) which is less dense? Which will form the top layer?
  8. What type of intermolecular forces are at play in limonene? How about water?
  9. How did the chemist know when to stop the distillation?
  10. Why was hexane added during the extraction process?
  11. When evaporating off the hexane why was the process stopped when the temperature rose to ~80 oC?
  12. What instrument in the Organic Laboratory could you use to remove the hexane?
  13. How would you dry the organic layer before evaporation?
  14. If the percent yield was 2.4% what was the mass of limonene recovered?
  15. Reflecting on the equation for distillation of immiscible liquids:

P Total = P°A + P°H2O = 1 atm = 760 mm Hg

Which component supplies the majority of the vapor pressure of the mixture? Why?

Which component has the higher boiling point?

Which component has the higher vapor pressure?

Why do you think steam distillation is a good method for isolating essential oils?

You obtained the IR spectrum of limonene below. Analyze the spectrum and assign peaks to show your compound is limonene.

 

IR of Limonene

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