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C. Additional tasks/instructions to carry out: 6) Include reaction scheme using Chemdraw for: the complete reaction showing the conversion of the reaction to the product (ii) Show the calculation of: a. the mass of the reactant used b. the number of moles of reactant and number of moles of product c. the mass of the final product d. the % yield of the product (iii) Include any observed odor and your inference (if any) (iv) Include snapshots of the two IR spectra (of the reactant and product) and circle and label the relevant peaks that prove the formation of the product and disappearance of the reactant.1
Banana Oil In this experiment you will be synthesizing an cster. Many of the simple esters have pleasant odors and many of the characteristic flavors and aromas of fruits and flowers are due to the presence of naturally occurring esters. Food and beverage manufactures have known this for many years and have often added synthetically produced esters to enhance the taste of their product. To be sure, a single ester does not produce the full flavor of a delicious fruit. It is often the naturally occurring combination of a dozen or more esters, carboxylic acids and other organic compounds that make up the pleasant tastes of many of the foods we eat. The ester that you will be synthesizing is isopentyl acetate also known as banana oil, the principal component of the taste and aroma of bananas. The esterification reaction involves the combination of and acid with an alcohol to produce an ester and water. In this case the acid will be acetic acid and the alcohol will be isopentyl alcohol, also named, isoamyl alcohol. H CHE CH3-C-OH + CH3-CH-CH2-CH2-OH Acetic acid Isopentyl alcohol (excess) (limiting reagent) + , -— CH-8.O.CH.CH сн. CH3-C-O-CH2-CH2-CH-CH3 + H2O Since the equilibrium of the above reaction does not favor the formation of the ester, it is shifted to the right by using an excess of acetic acid (Le Chatelier's principal). The excess acetic acid and any unreacted alcohol are then removed by extraction with water, then again with sodium bicarbonate and water. This extraction process involves your using a separatory funnel in which the denser layer that dissolves the excess acid and alcohol (the water or aqueous layer) lies below the organic layer which contains the ester. The organic layer, on top, is then finally extracted with aqueous NaCl (discarding the water layer all three times) and finally this organic layer is dried with anhydrous sodium sulfate and distilled to collect the isopentyl acetate at its boiling point. Chemists refer to the process of "cooking" a reaction mixture as refluxing. In refluxing any liquids that are boiled off do not escape the reaction vessel but are condensed back to a liquid and boiled over again and again. You will perform your reaction in a reflux apparatus so you should use the model reflux apparatus displayed in the front of the lab as your guide
Procedure Weigh (tare) an empty graduated cylinder and record its weight. (You may, alternatively, use the electronic balance that automatically subtracts the tare weight) Pour approximately 5.0 mL of isopentyl alcohol into the graduated cylinder and weigh it to determine the exact weight (four decimal places) of the alcohol. Record the weight. Remove the round bottom flask of the reflux apparatus and pour the alcohol that is in the cylinder into the flask. Without cleaning the graduated cylinder, pour 7.OmL of glacial acetic acid into the cylinder and add it to the alcohol in the flask. (BE CARE WHEN HANDLING GLACIAL ACETIC ACID AND CONC. SULFURIC ACID. IF IT SHOULD GET ON YOUR SKIN, IMMEDIATELY WASH IT OFF WITH LARGE AMOUNTS OF WATER). Measure ImL of concentrated sulfuric acid with a Pasteur pipette and also add it to the flask while gently swirling the flask to mix the four components. Add a corundum boiling chip to the flask and reattach the flask to the reflux apparatus. Allow water to slowly circulate in the condenser, turn up the voltage on the heating mantle so that the mixture starts to boil and continue heating under reflux for 60-75 minutes. Then tum off or remove the heating mantle and allow the mixture to cool to room temperature. While you're waiting, you should set up a ring stand containing a ring to hold your separatory funnel (See this set-up displayed in the front of the lab). The white stopcock should be in a horizontal position so that it is closed. When the cooling is complete carefully take apart the reflux apparatus. Remove the ground glass stopper from the separatory funnel and pour the contents of the round bottom reaction flask into the top separatory funnel (Try not to transfer the boiling stone) Add 10 mL of water to the funnel, put back the ground glass stopper and carefully shake the finel while frequently venting it while in the upside-down position. (Venting is done by turning the stopcock to the vertical position, but be sure that the funnel is inverted when you do this or you will lose your product) Let the two phases separate. Replace the funnel in the ring stand. Remove the ground glass stopper and let the lower, aqueous layer slowly drain into a beaker. You may discard the contents of the beaker only if you are sure that it contains the lower aqueous layer. For your second extraction you will add 5ml. portions of 5% aqueous sodium bicarbonate to the separatory funnel until mixture is basic to litmus. Now extract the organic layer once again exactly as you did before. Finally, you do a third extraction, but this time use SmL of saturated aqueous sodium chloride solution. There is a little bit of water in the organic layer in what we now refer to as the "crude ester". You can remove this water by transferring the crude ester to a clean, dry 25 ml Erlenmeyer flask and adding approximately 1 gram of anhydrous sodium sulfate. Place a cork into the flask and allow it to stand for 10-15 minutes while you set up the distillation apparatus. (Observe the model distillation set-up in the front of the laboratory) If the solution still looks cloudy or you see any droplets of water, transfer the crude ester to a new clean, dry flask and allow it to stand with the addition of about another half a gram of anhydrous sodium sulfate.
Be for you start the distillation you must weigh a small round bottom or Erlenmeyer flask in which you will collect your product. Record its weight. Then the collection flask should be placed in an ice bath at the end of the distillation apparatus to insure condensation and reduce odors in the laboratory. Look up the boiling point of isopentyl acetate in the Handbook of Chemistry and Physics. This is the approximate temperature to collect your product. Five degrees below and above the literature value should give you a pure product to collect. Continue to distill until only a drop or two remains in the distilling flask. Record the observed boiling range in your note book and note any odor that you smell. Weigh your final product and use this weight to calculate the percent yield of your reaction. Bring your product into the instrument room, carefully prepare a salt plate containing your product and under the guidance of a College Laboratory Technician obtain its infrared spectrum using the IR spectrometer. Record the name and model number of the spectrometer. Compare the spectrum of your product with that of the alcohol reactant which will be given to you by the technician. Write on the graph printout the identity of two or three peaks that characterize the identity of your product and do the same for the isopentyl alcohol.
Scans: 32 Resolution: 8.000 90 85 BO with 75 70 65 60 55 50 %Transmittance 45 40 1875.34 7 35 30 2953.42 25 20 15 3336.99 10 oon 1500 1000 500 5 -0 4000 3500 3000 2500 2000 Wavenurnbers (cm-1) Date: Thu Nov 02 14:52:48 2008 (GMT-05:Ocertified isopentyl alcohol Scans: 32 Resolution: 8.000
75 70 65 60 55 50 1469.01 104656 45 40 % Transmittance 35 30 1227.40 25 20 174247 1375 34 15 10 5 o O 1500 1000 500 4000 3500 3000 2500 2000 Wavenumbers (cm-1) Date: Mon Oct 28 12:34:56 2019 (GMT-05:CCHM 31 Isopentyl Acetate (Banana Oil) Scans: 32 Resolution: 8.000