Isolation of Acetyleugenol (Clove Oil) from Cloves
In this experiment, you will obtain the essential oil from cloves by steam distillation. You will then separate a component (acetyleugenol) from the oil by liquid-liquid extraction. Finally, you will isolate the acetyleugenol by using a rotovap for reduced pressure distillation, which will remove the organic solvent (dichloromethane).
Whole cloves contain between 14% and 20% by weight of essential oils, but only half of that can be isolated as acetyleugenol.
Clove oil contains two basic compounds: eugenol and acetyleugenol. As a result of Dalton’s Law and Raoult’s Law, both of these substances can be removed from the cloves with a steam distillation.
Eugenol is polar due to the acidic hydroxyl (OH) group, but acetyleugenol is not polar. As a result, they can be separated by extraction from a 5% aqueous NaOH solution. Acetyleugenol will dissolve in the organic CH2Cl2 layer, while eugenol remains in the aqueous base layer as a phenoxide. This can be seen in the reaction below (where ArOH is eugenol), because dissolved ions prefer the aqueous phase.
ArOH(aq) + OH-(aq) ArO-(aq) + H2O(Liq)
Acetyleugenol has no acid proton, and cannot ionize. So, it prefers the organic phase.
Essential oils from plant materials are used today for medicinal and other purposes. Among these oils are camphor, quinine, oil of cloves, cedarwood, turpentine, cinnamon, gum benzoin, and myrrh. The U.S. FDA has declared clove oil to be the most effective remedy for a toothache.
25 g whole cloves (350 g per lab section)
100 ml DI water (1.5 L per lab section)
10 ml 5% NaOH (150 ml per lab section)
45 ml CH2Cl2 (650 ml per lab section)
Mg SO4 or Na2SO4 (anhydrous)
Items in kit
250-ml round-bottomed flask
large bore condenser
125-ml separatory funnel
Items not in kit
100-ml graduated cylinder
stands and clamps
heating mantle (for 250-ml flask)
250-ml separatory funnel
125-ml Erlenmeyer flask w/ stopper
Place 25 g of whole cloves in a 250-ml round-bottomed flask, and add 100 ml of DI H2O. A plastic funnel can be used if necessary to transfer the cloves into the flask.
Set up a well-clamped simple distillation apparatus with the large bore condenser. Insert a Claisen adapter with a 125-ml separatory funnel between the flask and the distillation head, similar to Fig. 23.4 of Zubrick. Ensure the valve on the separatory funnel is closed. Then cover the flask, distillation head, and the bottom of the heating mantle with aluminum foil to insulate for a faster distillation rate.
Collect 60 ml of distillate. Also, simultaneously heat distilled water to ~90oC on a hot plate for addition in step 4.
Add 60 ml of hot H2O to the separatory funnel, then open the stopcock to add the water to the flask. Be sure to remove stopper from funnel before opening its valve. Also, be sure to close the valve after adding the water.
Collect another 60 ml of distillate.
Add 10 ml of 5% NaOH solution to the distillate to neutralize (deprotonate) the eugenol.
Acetyleugenol is not very soluble in H2O, and is easily extracted from the distillate with CH2Cl2. Place the 130 ml of distillate solution in a 250-ml separatory funnel and remove the acetyleugenol with three 15-ml portions of CH2Cl2.
Gently shaking the separatory funnel will fail to remove the acetyleugenol, however vigorous shaking will produce a boundary layer that is a visible organic- aqueous emulsion. Therefore, shake vigorously, and remove the lower layer up to, and not including, the emulsion.
Pressure typically builds inside separatory funnel when shaken! Be sure to vent stopcock frequently while shaking!
Do not vent towards yourself or any other individual!...
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