Eim A. Chemist
June 16, 2005
“Essential oils” are the volatile components associated with the aromas of many plants.1 In this experiment, the essential oil eugenol (the main component of oil of cloves) will be isolated from ground cloves using the technique of steam distillation, which is often used to isolate liquid natural products from plants.2 The principle of steam distillation is based on the fact that two immiscible liquids will boil at a lower temperature than the boiling points of either pure component, because the total vapor pressure of the heterogeneous mixture is simply the sum of the vapor pressures of the individual components (i. e. PT = PoA + PoB, where Po is the vapor pressure of the pure liquids). This leads to a higher vapor pressure for the mixture than would be predicted for a solution using Raoult’s Law (that is PT = PoANA + PoBNB, where N is the mole fraction of the component in the mixture). The higher total vapor pressure leads to a lower boiling point for the mixture than for either single component.2 During the isolation of a liquid natural product by steam distillation, water is one of the components, and the liquid natural product being isolated (which is immiscible with water) is the other component. The product can be steam distilled from the natural source at a relatively low temperature (always less than 100 oC), thus avoiding decomposition of the product.2
Steam distillation can be carried out in two ways: the direct method and the live steam method.3 In the direct method, steam is generated by boiling a mixture of the source of the compound of interest and water. The live steam method is carried out by passing steam from an external source into the distillation flask. The direct method of steam distillation will be used in this experiment and is carried out on a semi-micro scale using the apparatus shown in Figure 1 below:
Ground cloves and water will be charged into the distillation flask shown in the figure. The mixture will then be heated to boiling on a hot plate with an aluminum heating block and the distillate (a eugenol/water mixture) will be collected. The eugenol will then be separated from the water by extraction with methylene chloride. The methylene chloride solution will then be dried, decanted and evaporated to afford the liquid eugenol. The percent recovery from cloves will be determined, and is expected to be about 10%, based on literature data.5 The product will be analyzed by transmission infrared spectroscopy (IR) as a neat sample using NaCl plates6 to confirm its structure. This will be done in two ways: (1) by looking at the major absorptions in the spectrum and comparing them to a correlation table7 and (2) by comparing the spectrum to that of an authentic sample. The major IR absorptions are expected to be 3200 – 3500 cm-1 (OH stretch), 3000 – 3150 cm-1 (sp2 C-H stretch), 1600 – 1680 cm-1 (alkene C=C), and 1400 – 1600 cm-1 (aromatic C=C)7.
Table of Chemical Substances8
Methylene chlorideCH2Cl2Solvent84.93-97 oC39 –
40 oC1.32 g/mL
Sodium sulfateNa2SO4Drying agent------------
-10 oC254 oC1.06 g/mL
When heating a reaction apparatus, be sure that it is open to the air so that pressure build up and subsequent rupture of the apparatus does not occur.
When heating liquids, make sure the liquid is stirred (or a boiling chip is added) to prevent “bumping”.
When performing an extraction, make sure to vent the centrifuge tube often to prevent...