Experiment 2: Isolation of Eugenol from Cloves Background; Readings on Vapor pressure, Raoult’s Law from TRO: A mixture of the essential oils, eugenol and acetyleugenol, will be steam distilled from cloves. These compounds are isolated from aqueous distillate by extraction into dichloromethane. The dichloromethane solution is shaken with aqueous sodium hydroxide, which will react with eugenol, to yield the sodium salt of eugenol in the basic aqueous layer, and acetyleugenol in the organic layer. The basic aqueous layer can be acidified to re-extract eugenol from it.
And the organic layer can be dried and concentrated to yield acetyleugenol 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(applies for iscible mixtures) (that is PT = Po(A)n(A) + Po(B)n(B), 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. The boiling point of eugenol, an oil found in cloves, is 248 °C, but it can be isolated at a lower temperature by performing a co-distillation with water. Steam distillation allows separating substances at lower temperatures which is useful since many organic compounds tend to decompose at high temperatures which regular distillation would require.
For steam distillation to be successful, the material to be isolated must be insoluble in water. Usually these compounds have a low vapour pressure. After mixing them with water, however, the mixture will distil when the sum of the two vapour pressures reaches atmospheric pressure. It follows, then, that this must happen below the boiling point of water. Note that by steam distillation, as long as water is present, the high-boiling component vaporizes at a temperature well below its normal boiling point without using a vacuum.
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; (Note, the suspension boils when it’s vapor pressure is equal to the external pressure.
Since both the eugenol and the water are contributing to the vapor pressure of the suspension, the suspension will boil before either pure substance would normally boil. ) Since the distillate will contain both water and eugenol, the eugenol must be extracted from the water using an organic solvent. Once the eugenol is extracted into an organic solvent,the organic layer is separated from the aqueous layer and dried. The eugenol is finally isolated by evaporation of the organic solvent. When the sum of the separate vapor pressures equals the total pressure, he mixture boils and P =P(A) + P(B) Where PA is vapor pressure of pure water A PB is vapor pressure of pure B 1 Then the vapor composition is Y (A)= PA/P Y(B) =PB/P Dalton’s Law: PAV1 = nART1 and PBV2 = nBRT2 V1 = V2 and T1 = T2 n = moles, The ratio moles of B distilled to moles of A distilled is OH OCH3 OAc OCH3 Eugenol Acetyleugenol
Objectives: To extract Eugenol and Acetyleugeonol from cloves To separate the mixture of eugenol and acetyleugenol using their acid-? base properties. To characterize eugenol and acetyleugenol using TLC(Rf values) and
Refractive index. Glassware: Beaker to mass the cloves, Erlenmeyer flasks(2, 50-? ml), storage container+ distillation glassware(there should be an assembly in the fume hood) Procedure: Week 1: Steam Distillation Place 10 g of whole cloves (ground using a mortar and pestle by the teacher) in a 100-mL round-bottom flask, add 50 mL of water, and set up an apparatus for simple distillation- steam (will be set up in the fumehood and you can draw the set up while in the lab) will be generated in situ(50 ml of water added to the flask will generate the steam).
Heat the flask until boiling begins, then reduce the heat just enough to prevent foam from being carried over into the receiver. Use a 50-mL Erlenmeyer flask as a receiver(the distillate will collect in the flask thro a funnel) and transfer periodically your distillate to a 50-mL graduated cylinder. While you have removed one receiver, do not forget to replace the Erlenmeyer flask with a second one(that is clean and dry). 2 Caution: It is important that the cloves remain covered with water at all times. Or else, the cloves will burn and smoke!
Also, the distillation has to be steady. If not the mixture will foam and the foam will drop down the condenser into the receiving flask. And this would contaminate the distillate. Save the distillate in a tightly capped bottle for the following week. Week 2: Separation of Eugenol and Acetyleugenol via acid/base extraction Place the 50 mL of distillate in a 125-mL separatory funnel and extract with three 10-mL portions of dichloromethane. Combine the dichloromethane extracts and reserve 1 mL for thin layer chromatography. teacher will explain this step) To separate eugenol from acetyleugenol: pour back the dichloromethane extracts into the separatory funnel, extract the dichloromethane solution with 5% aqueous sodium hydroxide solution. Carry out this extraction three times, using 5-mL portions of sodium hydroxide each time. KEEP the aqueous extracts (it contains eugenol) and dry the organic layer over sodium sulfate (add enough so the drying agent no longer clumps together but appears to be a dry powder as it settles in the solution).
Swirl the flask to complete the drying process and let the drying agent settle for 1 minute before decanting into a DRY and TARED Erlenmeyer flask, rinse the drying agent with two 2-mL portions of dichloromethane. Evaporate the solution on a steam bath, the residue should be aetyleugenol. Acidify the combined aqueous extracts to pH 1 with concentrated hydrochloric acid (use Litmus paper to monitor the pH), and then extract the eugenol with three 5-mL portions of dichloromethane.
Dry the combined extracts over sodium sulfate, as done before, decant into a DRY and TARED Erlenmeyer flask, and evaporate the solution on a steam bath, the residue should be eugenol. Cleaning Up: Combine all aqueous layers, neutralize with sodium carbonate, dilute with water, and flush down the drain. Any solutions containing dichloromethane should be placed in the halogenated organic waste container. Wash up all glassware with soap and water. Analysis: Calculate the weight percent yields of eugenol and acetyleugenol oils based on the weight of cloves used. Analyze your products sing refraction index. Analyze your products using thin layer chromatography (TLC). Eluent: dicloromethane-hexane (1:2 or 2:1)
Vizualization: under UV light and iodine chamber AS Co AE AS – Acetyleugenol Standard Co – Co-spot AE – Acetyleugenol Extract ES Co EE ES – Eugenol Standard Co – Co-spot EE – Eugenol Extract ES Co CM ES – Eugenol Standard Co – Co-spot CM – Crude Mixture First a TLC plate is prepared by spotting the purified unknown and an authentic sample of each possible compound. Then the TLC plate is developed. For the next step (co-spotting), an authentic sample of the 3 ompound closest in Rf value to the unknown is chosen. TLC co-spotting of a second plate allows for preliminary identification of your compound. Three spots are applied to the adsorbent on the baseline of the TLC plate: the purified unknown, an authentic sample, and a co-spot of unknown and authentic sample. If the developed TLC plate shows only one row of spots, it can be concluded that the unknown has been purifed, and that the unknown is possibly the same compound as the authentic sample.
However, because Rf values are relative, not absolute, some compounds may have very similar Rf values Pre-? ab: FOR WEEK 1 only: All the required formulae for the caculations have been presented here. Hence googling is not required. MSDS is required for the following chemicals: Eugenol and acetyl eugenol. Pre-? lab should be complete to the best of your ability before the lab. Answers will be discussed during the lab. For the procedure : You will draw the glassware set up when you come to the lab; Just come prepared with titles, objectives, MSDS. Questions from pre-lab should ensure that you have understood the theory behind WEEK 1 ; Distillation. 1a. What is the vapour pressure of benzene at 80 egrees celcius. Explain the term vapour pressure. 1b. What is an azeotrope? How would the term azeotrope apply in this experiment? 2a. The vapor pressure of water at 99oC is 733 torr. What is the vapor pressure of eugenol that codistills at this temperature? The amount of the substance X that co-? distills together with the water is given by Pwater/px = nwater/nx n(water) = moles of water n(X)= moles of Eugenol 2b. Calculate the mass of eugenol that co-distills with each gram of water at 99oC. How many grams of water must be distilled to steam distill 2 grams of eugenol from an aqueous solution?
Calculate mass% for both eugenol and water. 3. What is the difference between essential oil and fatty oil? What would be suitable IUPAC name for eugenol and acetyl eugenol? 4. Based on the formulae presented so far, cite one disadvantage of steam distillation of organic compounds. 5. Steam distillation may be used to separate a mixture of 4-? nitrophenol and 2-? nitrophenol. The 2-? nitrophenol distills at 93 degrees but the 4-? nitrophenol does not. Explain. 6. List your observations during the lab: Record the temperatures at various times, nature of the distillate, odour….. 4
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