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Objective
The aim of this experiment was to extract essential oils from the cloves by steam distillation and identifying the volatile compounds present in the extracts.
Introduction
Essential oils are volatile, ethereal oily liquids that have been in use even before the days of advanced organic chemistry. They are usually extracted from plants depending on the nature of the plant by many techniques, including distillation, cold-press, solvent, supercritical fluid extraction and enfleurage. Most essential oils can be extracted by application of direct or indirect steam distillation. Steam distillation is an extraction technique that uses steam to separate mixture components. The oils have odors that are highly characteristic of the plants from which they are extracted, and for this, they were assumed to be the essence of the original plants, hence the name essential oils (Parthasarathy, Chempakam and Zachariah).
The main ingredient found in the essential oil extracted from the cloves is Eugenol. Eugenol has many applications, ranging from perfumery to the manufacture of synthetic vanillin, from dental analgesic to antiseptic. Other important constituents in the essential oils found in cloves include; acetyl eugenol, vanillin; crategolic acid; beta-caryophyllene, gallotanic acid, tannins, methyl salicylate; kaempferol, the flavonoids eugenin, eugenitin and rhamnetin; triterpenoids like stigmasterol, oleanolic acid and campesterol; and other several sequiterpenes (Belitz, Grosch and Schieberle).
Eugenol is a substituted methoxy phenol chemical compound that has a similar structure as that of vanillin. However, eugenol has an allylic functional group in the para position in place of the aldehyde. The allylic functional group forms a chain that gives euginol compound its characteristic strong odor.
The difference between essential oils and fatty acids is their volatility and non-greasiness. In addition, they are not saponifiable, i.e. they cannot be used to make soap. Essential oils impart specific odors to leaves, flowers or woods For example, juniper oil, cedar oil, peppermint oil, oil of turpentine etc. They can also be developed by enzyme action on plant components. These oils are normally soluble in ether and alcohol, flammable and slightly soluble in water, and can contain esters, acids, hydrocarbons, ketones, alcohols, aldehydes, phenols and ethers (Williams).
In this experiment, the steam distillation apparatus was used in extraction of essential oils from cloves, followed by identification of volatile components in the extracted essential oils by utilizing GCMS. The chemical compounds in the essential oil were identified by comparing the molecular mass fragmentation patterns with those available at the Saturn 2200 GCMS library.
Experimental Procedure
Steam Distillation:
The distillation apparatus was prepared using a 500 Ml round-bottom flask, steam distillation head, condenser and receiver. The flask was then filled up with 50 Ml of water and 20g of cloves, and then the contents distilled to collect 100 Ml of the distillate. Using 10Ml dichloromethane, the cooled distillate was extracted. Once the dichloromethane layer had separated from the aqueous layer, a long Pasteur pipette was used to remove the lower layer. The dichloromethane extract was then dried by passing it in a Pasteur pipette that was filled with 4 cm of dried magnesium sulphate. The figure below shows how the apparatus was set-up during the experiment.
GCMS:
The micro-syringe was rinsed with a diluted extract of essential oils from cloves. The GCMS was set and loaded with the gas chromatography and mass spectroscopy method as described in the “CTEC2101” folder. 1µL of a sample of extracted essential oils was then injected and the GCMS run and the resulting spectrum analyzed.
Results and Discussion
The distillation technique is an effective method of extracting components of essential oils with high boiling points as high as 200oC, yet the oil vapors are close to 100oC. This preserves the structural integrity of the essential compounds by allowing the distillation process to occur at temperatures below the actual boiling points of the components. Steam vaporizes the essential oils while the hot vapors condense into a liquid, along with water after passing through the cooling vessel. Since the essential oils are immiscible in water, two layers of distillate are formed; an oil layer and a water layer. The oil usually floats on water due to its low density. This makes it possible to siphon the aqueous layer using a separatory funnel (Pavia, Kriz and Lampman). Development of an emulsion, as is often the case in a small scale distillation, the characteristic immiscibility of the hydrophobic essential oils makes extraction of a non-polar organic solvent product highly effective.
Essential oil from clove was tested using gas chromatography/mass spectrometry (GCMS) to identify the compounds present in the oil and purity. The figures 1 and 2 below shows GCMS chromatogram illustrating identifying characteristics of the essential oils.
Identification of Components of the essential oils
Using library searches, interpretation and identification of components of the essential oils on mass spectrum GCMS can be ascertained. The spectrum of unknown components in the essential oils was compared with a matching spectrum of known components stored in the library search facility. The figure below shows the comparison of the two spectra that were found to have a match.
The chemical compounds present in essential oils from clove represented in table 1 below. The compounds have been identified by comparing to the results of molecular weight from the search library.
Table 1: The main composition of essential clove oil
Compound Identified Molecular Weight (Saturn 2200 GCMS library) Molecular Weight (Identified compound) Molecular Formula
Eugenol 164.0 164.2 C10H12O2
Carvacrol 147.0 149.1 C10H14O
Benzoic acid 137.0 133.2 C8H8O2
2-Heptanol 103.0 103.0 C7H16O
The major component of the extracted essential oil from clove is eugenol. Other constituents include carvacrol, benzoic acid and 2-hetanol. Identification and characterization of essential oil extract has been conducted by comparing the spectral molecular masses of the unknown compounds with those of a matching spectrum from the search library. Eugenol comprises the highest percentage of the essential oils (>85%). It is the constituent responsible for the strong aroma of clove oil. Other components of essential oil extracted from cloves may be present in the sample, but at relatively low percentages.
Sources of Errors
Errors in this experiment may have resulted from use of unclean glassware, which may have resulted to side reactions. Also, if the cloves are not well grounded, it will affect the quantity of yield. The cloves have to be distilled long enough at sufficiently enough temperatures. Having loose connections between the glassware can reduce the quantity of oil yield.
Improving the Experiment
The main challenge in this experiment was to extract sufficient quantities of essential oils from clove. This can be improved by combining samples from other students to obtain sufficient amount of essential oils for analysis. Other alternatives that can be used to characterize the product include; retention times and peak are percentage.
Conclusion
Four constituents were identified in the essential oil extracted from clove; Eugenal, Carvacrol, Benzoic acid and 2-Heptanol. Eugenol comprises the largest percentage of the essential oils extracted from the cloves. It comprises more than 85% of the essential oil. Eugenol is the compound that is responsible for the strong aroma of the cloves. This procedure provides a relatively easy method of extraction and characterization of essential oils from cloves.
References
Belitz, H.-D., Werner Grosch and Peter Schieberle. Food Chemistry. United Kingdom: Springer Science & Business Media, 2009.
Parthasarathy, V. A., Bhageerathy Chempakam and T. John Zachariah. Chemistry of Spices. United Kingdom: CABI, 2008.
Pavia, Donald, et al. A Microscale Approach to Organic Laboratory Techniques. U.K: John Wiley & Sons, 2012.
Williams, Cheryll. Medicinal Plants in Australia Volume 2: Gums, Resins, Tannin and Essential Oils. Australia: Rosenberg Publishing, 2011.
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