LAB 17: SYNTHESIS OF BANANA OIL: REACTIONS OF ALCOHOLS: FISCHER ESTERIFICATION

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1 LAB 17: SYNTESIS F BANANA IL: REATINS F ALLS: FISER ESTERIFIATIN PURPSE: To synthesize isoamyl acetate by Fischer Esterification. To purify a liquid by simple distillation. SAFETY NERNS: Always wear safety goggles. Sulfuric Acid and Glacial Acetic Acids are dangerous to skin eyes, mucus membranes and clothes. Use these with caution. If contacted, wash with soap and copious amounts of water. ESTERS: Volatile esters usually have pleasant, fruity odors. The characteristic fragrance and flavor of fruits and flowers are due, in most cases, to mixtures of esters. The mixture of esters responsible for a natural flavor is usually complex and difficult to duplicate. owever, if the flavor is attributed to a major component then a synthetic ester of the same structure can be substituted for the natural flavor at a fraction of the cost. For this reason, esters are used in the food, flavor, and fragrance industries. A formula for artificial pineapple flavor is given below. The composition of the mixture is very important to duplicating the flavor; and it should also be pointed out that our perceptions of an ester s smell may depend on its dilution. ARTIFIIAL PINEAPPLE FLAVR Pure ompounds % Essential ils % allyl caproate 5 oil of sweet birch 1 isoamyl acetate 3 oil of spruce 2 isoamyl isovalerate 3 balsam Peru 4 ethyl acetate 15 volatile mustard oil 1 ethyl crotonate 5 oil cognac 5 ethyl butyrate 22 concentrated orange oil 4 terpinyl propionate 3 distilled oil of lime 2 caproic acid 8 butyric acid 12 acetic acid _5 81 When alcohols are combined with carboxylic acids in the presence of an acid catalyst an esterification reaction occurs to form esters and water. The reverse reaction, hydrolysis, decomposes an ester into a carboxylic acid and an alcohol. Esterfication and hydrolysis are in equilibrium. Thus, the ester product is favored when an excess of acid or alcohol is used or when water or the ester is removed as soon as it forms. Addition of excess water shifts the equilibrium toward hydrolysis. Esterification 19 arboxylic Acid Alcohol Ester Water propanoic acid (propionic acid) ethyl alcohol (ethanol) water 105 Lab 17: Synthesis of Banana il (F15) 73 ethyl propanoate (ethyl propionate) ydrolysis

2 The name of an ester indicates the acid and the alcohol that combined to form it. The first word in the name comes from the alkyl group of the alcohol, and the second word is the name of the acid with its ic ending changed to ate. The structures and approximate smell of a few esters follow: Name Flavor Structure isoamyl acetate banana methyl butyrate n-propyl acetate isobutyl propionate ethyl butyrate octyl acetate apple pear rum pineapple oranges ( 2 ) 6 3 Many esters can be conveniently prepared by refluxing a mixture of a carboxylic acid and an alcohol in the presence of a strong mineral acid such as sulfuric acid or hydrochloric acid. The acid catalyst increases the rate at which equilibrium is reached but does not affect the position of the equilibrium. In order to shift the equilibrium to the right and prepare the ester in reasonable yield two measures can be taken: 1) use a large excess of the alcohol, or 2) remove either the water or ester as it is formed. The most common method of the two, especially when the alcohol is inexpensive as is the case for methanol and ethanol, is to use an excess of the alcohol. This procedure is call Fischer Esterification. In this lab we will be making isoamyl acetate according to the following equilibrium reaction: Because the reaction is in equilibrium there will be a mixture of compounds that must be separated from each other to isolate the final ester product. Esters are usually insoluble in water so form a separate layer than can be isolated using a separatory funnel. PURIFIATIN METDS: Very few materials we encounter are pure. The beverages we drink, the fuel for our automobiles or stoves, and the ground we walk on are all mixtures of various elements or compounds. Any material made up of two or more substances that are not chemically combined is a mixture. The isolation of pure components from a mixture requires that the individual substances be separated from one another. The following list gives several common methods used to separate the components of a mixture Lab 17: Synthesis of Banana il (F15)

3 1. Filtration is used to separate an insoluble solid from a liquid. A simple way to separate a solid from a liquid is to strain the mixture through a porous filter material like paper, charcoal (carbon), glass wool, cotton, or cloth. The solid will remain in the porous filter and the liquid will pass through. The liquid that passes through is called the filtrate. The solid remaining on the porous material is the residue or precipitate. Filtration is useful when separating tea leaves from tea, or coffee grounds from a coffee drink. 2. Decantation is used to separate a liquid from insoluble solid sediment that has settled to the bottom of the container. The liquid is carefully poured off without disturbing the solid. Decantation is a quick and easy way to separate, however it seldom results in a complete separation of the solid from the liquid. It is useful when crude separations are appropriate as decanting wine off of sediment or pouring sea water off of sand. 3. Solubility Extraction occurs when a solvent selectively dissolves one component of a mixture but does not dissolve the other. For example, if water was added to a mixture of the solids salt and sand, the salt would dissolve but the sand would not. The Dissolved salt could then be filtered or decanted away from the sand. To recover the salt as a solid the water can be evaporated or distilled away. 4. Evaporation separates a volatile (easily vaporized) liquid from a nonvolatile (difficult to vaporize) solid. eat will turn the volatile liquid to a gaseous vapor that will be driven off into the atmosphere leaving the remaining solid component behind. This would be an ideal method for separating salt from sea water as water can easily be vaporized but salt can not. 5. Distillation is a common way to separate volatile (easily vaporized) substances from other less volatile or nonvolatile substances. Besides separating a liquid from a solid, a mixture of liquids can be separated as well. If a mixture is composed of two liquids, the one with lower boiling point can be removed from the other by distillation. As the mixture is heated its temperature rises and the lowest boiling liquid begins to vaporize first. The vapors are then cooled and recondensed back into liquid and are caught in a separate container. The liquid that is caught is called the distillate. As the distillation continues and most of the lower boiling component is distilled off, the temperature of the mixture will rise and the higher boiling component will begin to distill. If the higher boiling condensed liquid is caught in a different container than was the lower boiling liquid, then the two liquids distillates will be separated. 6. Fractional rystallization occurs when one compound of a mixture is less soluble than the other in a certain solvent. For example, Listerine mouthwash is a solution that contains many compounds dissolved in water. If Listerine is cooled in ice, however, benzoic acid becomes less soluble and starts to turn solid. The cold Listerine looks cloudy due to the suspended benzoic acid solids. The solid could then be filtered away from the water solution and thus separated. In this laboratory experiment we will attempt to purify a mixture that contains soluble and insoluble ionic impurities. We will use Solubility extraction Filtration through paper, and Distillation. 105 Lab 17: Synthesis of Banana il (F15) 75

4 PREDURES: ATINS: I. ISAMYL AETATE (Banana il): 1. Into a dry ml round bottom flask (rbf) add: 12 ml of isoamyl alcohol 2 and 20 ml of glacial acetic acid 3 ( ) arefully add 1 ml of concentrated sulfuric acid 4 ( 2 S 4 ) while swirling. 2. Add boiling stones 5 and assemble the apparatus for reflux placing the boiling flask high enough above the burner (6-8 inches) to get moderate heating rather than high heat. 6 Gently reflux for at least 30 minutes. 7 (Read ahead to get ready for procedures coming up.) 3. Allow the flask to then cool at room temperature until cool enough to handle (about five minutes). 4. Pour the mixture into a separatory funnel and add 10 ml of cold water (distilled water chilled in an ice bath) to wash 8 the oil. Gently shake the layers and then let stand to allow the layers to separate. 9 (If Layers are not visible add more water to the separatory funnel without further shaking.) 5. Remove and discard the lower, aqueous layer but keep the top organic layer in the separatory funnel To further wash the banana oil layer in the separatory funnel add another 10 ml portion of cold water to the organic oil, shake the layers and separate them again. Discard the aqueous layer but keep the top organic layer. 7. Wash the oil again but this time slowly add 10 mls of saturated sodium bicarbonate 10 (Na 3 ), to the top organic layer in the separatory funnel. Shake with frequent burping and separate again. Discard the aqueous layer but keep the top organic/oil layer. 8. Now wash the oil layer with 10 mls of saturated sodium chloride 11 solution (Nal). 9. Transfer the organic layer to a 125 ml Erlenmeyer flask and dry 11 it for five minutes over anhydrous magnesium sulfate (MgS 4 ) or anhydrous sodium sulfate (Na 2 S 4 ). 10. Decant the dried solution (or filter through a fluted 12 filter paper) into a 50 ml round bottom flask (rbf) using a stirring rod 13 if needed to direct the oil. 11. Purify the banana oil by simple distillation. NTES: 1 Any water present will serve to shift the equilibrium back toward reactants and away from the desired product esters. 2 The IUPA name of isoamyl alcohol is 3-methylbutanol. Another common name is isopentyl alcohol. 3 The IUPA name of Acetic acid ( 2 3 2) is Ethanoic Acid. Glacial acetic acid refers to the concentrated form. 4 oncentrated Sulfuric Acid ( 2S 4) is dangerous to your skin, eyes, and clothes. Do not breathe the vapors. Wash hands with soap and water immediately if contacted. 5 Boiling stones create a surface on which vapors can collect in order to produce a smooth and even boil. Without them there is potential for bumping and uneven boil. Magnetic stir barring bars can also be used if available. 6 Apparatus for reflux: 7 Reflux allows a reaction mixture to boil without the substances evaporating away. This enables continued heating so equilibrium can be established. ne hour is preferred. 8 When water or aqueous solutions are mixed with organic oil mixtures the purpose is to wash the water soluble compounds away from the organic oil thus purifying the oil. Acetic acid and sulfuric acid are miscible with water. The solubility of isoamyl alcohol is 2.7 ml/100 ml water and isoamyl acetate is 0.25 ml /100 ml water which means they will remain in an insoluble layer without dissolving in the amount of water in the washes. 9 The separatory Funnel is a tool for separating two layers. The bottom more dense layer containing water (d=1g/ml), acetic acid (d=1.049g/ml), & sulfuric acid (d=1.84g/ml) drains out the bottom and the top less dense layer containing isoamyl alcohol (d=0.815g/ml) and isoamyl acetate (d=0.876g/ml) goes out the top. Water out Water in 10 Sodium bicarbonate (a base) will react with any leftover acids (acetic acid & sulfuric acid) to turn them into water soluble salts that will wash away into the water layer Na 3 Na S 4 + Na 3 Na 2S Sodium chloride, magnesium sulfate, and sodium sulfate attract water like a sponge taking it away from the oil layer to dry it. 12 To flute filter paper: 1) fold in half 2) fold again into quarters 3) fold back and forth from the point as if making a fan 4) unfold the paper into a cone that will fit into a funnel. 1) 3) 4) 2) oil water 13 The stirring rod helps to channel the flow of liquid to prevent dripping Lab 17: Synthesis of Banana il (F15)

5 II. SIMPLE DISTILLATIN 1. Get 2 small dry graduated cylinders ready to use as collection (receiving) containers. 14 Accurately suspend the thermometer so that the temperature of the vapor is measured just as it comes to the condenser. 2. lamp the 50 ml rbf of oil to a ring stand about 6-8 inches above a laboratory burner. Add boiling stones 5 and set up a glass simple distillation apparatus 14 equipped with a thermometer, and water-cooled condenser 15. Place the first collection container at the end of the condenser. 3. eat the flask over the low flame of a Laboratory burner. When the solution begins to boil make note of the temperature and watch the temperature rise to the point where the vapors are gathered around the thermometer and start condensing. 4. When the temperature approaches the boiling point of isoamyl alcohol 16 collect the distillate in a clean dry graduated cylinder, while continuing to observe the temperature. Report your experimental boiling point of isoamyl alcohol as the range in which the temperature remains relatively constant or levels off (plateaus). 5. As soon as the temperature rises beyond the boiling point of isoamyl alcohol trade collection containers and collect the isoamyl acetate in the second graduated cylinder and record the boiling point (also as a range). Do not let the flask boil completely dry When the crude oil is nearly gone (without going dry) 17 stop the distillation. 7. Determine the mls (yield) of any isoamyl alcohol and of any isoamyl acetate product. 15 The water needs to be turned on just enough to maintain a continuous flow through the condenser. If it is on too strong the water pressure will pop off the hoses and water will spray everywhere. 16 The crude oil collected is a mixture of unreacted isoamyl alcohol (bp 130 o ) and product isoamyl acetate (bp 142 o ). The unreacted acetic acid (bp 118 o ) and the sulfuric acid catalyst (bp 290 o ) have been previously washed away into the water layers in the separatory wash steps. 17 Never let the boiling flask boil completely dry. Without liquid in it the glass flask would heat to a much higher temperature. The alcohol thermometer and possibly the Pyrex glass could break. 8. alculate the % yield of isoamyl acetate, and turn in the product. III. ENMI ANALYSIS: Assume you are entering a fragrance business where you intend to make and sell fragrant potions such as banana oil (isoamyl acetate). 1. onsult the Aldrich hemical atalogue to determine and record the cost of the reactants used. 2. onsult the Aldrich hemical atalogue for the market value of your banana oil (isoamyl acetate). 3. Based on the amount of isoamyl acetate product you actually produced determine the net profits from the sale of your banana oil. 105 Lab 17: Synthesis of Banana il (F15) 77

6 Lab 17: Synthesis of Banana il (F15)

7 LAB 17: SYNTESIS F BANANA IL: PRE LAB EXERISES: NAME DATE 1. When water is heated in the distillation process the temperature eventually reaches a constant value and forms a plateau when graphed. What does the plateau indicate? A. The limit of the thermometer used. B. The boiling point.. The value of the heat of vaporization. 2. Match each of the following descriptions with the term it best describes: A. Distillate B. Distillation. Filtrate D. Filtration E. Decant F. Residue The process where a volatile substance is separated from a less volatile substance by heating to vaporize and then recondense. The liquid that has been vaporized and recondensed and collected from the distillation process. To pour the liquid off of an insoluble solid without disturbing the solid. The solid that has been collected in the porous material during the filtration process. The liquid that has passed through a porous material. 3. omplete the structures of the starting materials and product for the following reaction: Esterification arboxylic Acid Alcohol Ester Water Name Acetic Acid Name _Isoamyl Alcohol isoamyl acetate water 4. omplete the following table of names and properties for the reactants and products: Show calculations when requested. Names Acetic Acid Isoamyl Alcohol Isoamyl Acetate M.W. (g/mol) Boiling point ( o ) Density (g/ml) Solubility (ml/100 ml 2) Amount of Reactants used (in mls and mols) mls used mols used; show calculations mls used mols used; show calculations Amount of Product expected (in mols and mls) mols expected; mls expected; show calculations 105 Lab 17: Synthesis of Banana il (F15) 79

8 Lab 17: Synthesis of Banana il (F15)

9 LAB 17: SYNTESIS F BANANA IL REPRT: Results: dor/ bservations Isoamyl Alcohol (recovered reactant) NAME PARTNER DATE Isoamyl Acetate (product) Boiling Point ( o ) Theoretical bp from literature Actual bp from experiment Theoretical bp from literature Actual bp from experiment Amount obtained Actual Yield recovered in mls Actual Yield produced in mls Amount expected Percent Yield (Theoretical yield mls from prelab calculations) Show calculations Actual X 100 = Theoretical Analysis: Economic Analysis: onsult the Aldrich hemical catalogue to determine the cost for 100 ml units of reagent grade ingredients. Reactants mls used Price/100 ml ost (of reagents you used) Isoamyl alcohol mls used Acetic Acid (glacial) mls used Total cost of reagents = Products mls made Price/100 ml Market value of product (of what you made) Isoamyl acetate mls made Market value of product = Net Profit = Analysis/onclusion: Advise from an economic/business perspective. 105 Lab 17: Synthesis of Banana il (F15) 81

10 RELATED EXERISES: 1. Why did the procedures used in preparation of banana oil require you to wash your product with water? 2. Why did the procedures used in preparation of banana oil require you to wash your product with sodium bicarbonate? 3. Write the balanced equations for the reactions of sodium bicarbonate with the following components of the product mixture: Account for any gas produced. A. With Acetic acid B. With Sulfuric acid 4. A. Why did the procedures used in preparation of banana oil require you wash your product with a saturated sodium chloride solution? B. Explain what the sodium chloride is doing and how it works. 5. A. Why did the procedures use in preparation of banana oil have you add anhydrous sodium sulfate or anhydrous magnesium sulfate to your product before distillation? B. Explain what these are doing and how they work Lab 17: Synthesis of Banana il (F15)

Experiment 12: Grignard Synthesis of Triphenylmethanol

1 Experiment 12: Grignard Synthesis of Triphenylmethanol Reactions that form carbon-carbon bonds are among the most useful to the synthetic organic chemist. In 1912, Victor Grignard received the Nobel