Isolation and Identification of Eugenol: The Fragrant Component of Cloves *Adri, Kiersten Jayne R. , Aguinaldo, Samuel Jr. Group 2 Department of Chemistry, College of Science University of Santo Tomas, Espana, Manila 1008 Abstract. In this experiment, the primary objective was to isolate eugenol from cloves. An amount of 30 grams of dried cloves and 300 mL of water was distilled over a flame for over 2 hours. The distillate underwent extraction with dichloromethane, water and sodium hydroxide. Concentrated hydrochloric acid was added to the aqueous extract to lower it to pH 9; it was again extracted with 2 x 30 mL of DCM.
These organic extracts were dried over anhydrous magnesium sulfate, filtered into a pre-weighed flask and had their solvent removed on the rotary evaporator. The amount in grams of the eugenol obtained was 0. 4770 g, which gave a % yield of 1. 578 %. INTRODUCTION Cloves are small, tropical evergreen trees (Syzygium aromaticum or Eugenia caryophyllata) which are members of the myrtle family. Its unopened flower bud is considered as an important spice which is dried and used whole or ground for cooking. The clove bud’s aroma and medicinal uses are attributed to the distillate of the oil of cloves, or eugenol.
Eugenol is an aromatic liquid which can either be colorless or yellowish in color, with molecular formula CH2CHCH2C6H3(OCH3)OH. It is known for its pleasantly spicy aroma. Eugenol comprises 72-90% of the essential oil extracted from cloves, making it the main component. Eugenol is used in perfumes, flavorings, essential oils, in medicine as a local antiseptic and anesthetic, and in the production of isoeugenol for the manufacture of vanilla. When mixed with zinc oxide, eugenol forms a material which has restorative and prosthodontic applications in dentistry. METHODOLOGY
The materials used in this experiment were the following: 30 g of dried cloves, 400 mL of water, 2 portions of 2 x 30 mL dichloromethane, 2 x 50 mL sodium hydroxide, concentrated hydrochloric acid, anhydrous magnesium sulfate, distillation set-up (500 mL round bottom flask, condenser, adapter, thermometer jacket, rubber tubing, tripod, Bunsen burner), Erlenmeyer flasks, separatory funnel and dropping pipettes. Figure 1. Steam Distillation Set-Up. Figure 2. Extraction Set-Up In a 500 mL round bottom flask, 30 g of cloves were placed along with 300 mL of distilled water.
The mixture was distilled over direct heat until 200 mL of distillate was collected. The oily distillate was transferred to a separatory funnel and extracted with 2 x 30 mL DCM. The combined organic layers were washed with 100 mL distilled water, extracted with 2 x 50 mL of 3M sodium hydroxide and lowered to pH 9 with concentrated hydrochloric acid. The milky aqueous mixture was extracted with 2 x 30 mL DCM, and the organic layer was collected and dried over anhydrous magnesium sulfate. The solution was filtered into a pre-weighed flask and its solvent was removed on the rotary evaporator. RESULTS AND DISCUSSION Weight of sample: 30. 145 g Distillate: White oily and milky solution 1st extraction with DCM Upper layer: (aqueous – white sticky solid mixture) Lower layer: (organic – DCM, clear) 2nd extraction with NaOH Upper layer: (aqueous – NaOH) Lower layer: (organic – DCM, clear) Addition of concentrated HCl Formation of white milky aqueous solution (pH 9) 3rd extraction with DCM Upper layer: (aqueous – white milky solution) Lower layer: (organic – DCM) Pre-weighed flask: 82. 0231 g Pre-weighed flask + organic extract : 82. 5001 g Experimental Yield: 0. 4770 g % Yield : 1. 79 % Eugenol was isolated from cloves by steam distillation. Since eugenol is not soluble in water, the concentration of the eugenol in the vapor over the boiling eugenol–water suspension does not depend on concentration of the eugenol. The relative amounts of eugenol and water in the vapor simply depend on the vapor pressures of the pure materials. The vapor pressure of water at 100 °C is 760 torr, and the vapor pressure of eugenol at 100 °C is approximately 4 torr; therefore, the vapor is roughly 0. 5 % eugenol. The suspension boiled when its vapor pressure was equal to the external pressure.
Since both the eugenol and the water contributed to the vapor pressure of the suspension, the suspension boiled before either pure substance would normally boil. Since many essential oils contain liquids that may not survive heating at higher temperatures, steam distillation is an especially advantageous technique for isolating them because their immiscible mixture with water boils below 100 °C. Figure 3. Structure of Eugenol Since the distillate contained both water and eugenol, the eugenol was extracted from the water using DCM and NaOH. After obtaining the oil of cloves by steam distillation, the eugenol was isolated by extraction.
In this process the fact that eugenol, because it is a phenolic compound, is weakly acidic whereas both eugenol acetate and caryophllene are neutral was considered. Thus, when the clove oil was treated with a sodium hydroxide (a strong base) it resulted in the selective formation of the sodium salt of eugenol which was soluble in the aqueous phase. The other neutral compounds did not react with sodium hydroxide and therefore remained in the organic phase. After the separation of the aqueous phase, its extraction with DCM and its acidification, the organic extract was dried over anhydrous magnesium sulfate.
The eugenol was finally isolated by evaporation of the organic solvent in the rotary evaporator. CONCLUSION From the cloves, 0. 4770 g of eugenol or 1. 578% was extracted. Although the procedures were followed word per word, the % yield was considered too small, because eugenol usually comprises 72% to 90% of the oil of cloves (distillate). REFERENCE/S Pavia, Lampman, Kriz, and Engel. (1999) Introduction to Organic Laboratory Techniques: A Microscale Approach. USA: Saunders College Publishing. Pavia, D. Organic Laboratory Techniques, 2nd edition. (1995). USA: Harcourt Brace & Company.