Many naturally occurring chemicals have the right to be provided isolated and used come make various other compounds. Methyl salicylate is a naturally developing compound that we will use to create salicylic acid, which will then be used to make the wonder medicine aspirin (acetylsalicylic acid). This is not the resource of salicylic mountain in the industrial synthesis of aspirin, but it is, nevertheless, a good one for activities use. Two various chemical techniques will be employed. First is hydrolysis, which is the break of a bond with water. Esters room quite conveniently hydrolyzed right into their two beginning components, an acid and an alcohol. Then, we do an ester synthesis for the formation of aspirin. Equilibrium favors hydrolysis, but using acetic anhydride together the acid resource prevents this behind reaction, due to the fact that water is not developed during ester formation. Both salicylic acid and aspirin are quickly isolated.
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BackgroundMethyl salicylate (an ester) deserve to be hydrolyzed to create salicylic acid. The two different functional teams on the aromatic ring are utilized in this lab. First, the free carboxylic acid group will be produced when we hydrolyze the methyl salicylate. Methanol is the alcohol which is exit by hydrolysis. Second, the hydroxyl team on salicylic acid will be supplied in ester formation to produce aspirin. As soon as we perform an ester synthetic previously, we took unique precautions to stop water native being produced (we consisted of a dessicant in the reaction mixture and also had a drying tube affixed on optimal of the reflux column). Acetic anhydride will certainly be offered in this experiment so that as soon as ester is formed, water is no produced. Together a result, the thermodynamic equilibrium will currently be because that the development of one ester instead of that hydrolysis. Before proceeding through the experiment you need to review number of items. First, you should be acquainted with the ester sensible group. Esters are created when one acid and also an alcohol combine. Girlfriend should be able to quickly determine an ester by looking in ~ the structure formula. Over there are just three species of link which have an oxygen located between two carbons. These space ethers, esters and also acid anhydrides. Have the right to you recognize the differences? Second, us will execute a hydrolysis reaction. Hydrolysis occurs once water is used to break a bond. Hydrolysis can take place in either basic or acidic conditions. We will learn later on the yes, really mechanisms, however in both cases we develop one chemistry which is an alcohol and also the various other chemical will be a carboxylic acid once esters space hydrolyzed. Third, we will create an ester. It must be detailed that ester development cannot happen in the presence of base, just acid. Throughout the very first day that this lab, we will create salicylic acid. This acid will certainly then be supplied to do aspirin. The synthesis of aspirin is a multi-billion dollar a year chemical. If salicylic mountain as some therapuetic value, it is not as efficient as aspirin in to reduce inflammation and other typical medical conditions for i m sorry aspirin can be used. Aspirin is component of a big group of chemistry classified together Non-Steriodal Anti-Inflammatory medicine (NSAIDS).
ProcedureThis experiment is composed of two parts. The very first involves the hydrolysis the methyl salicylate in stimulate to develop salicylic mountain (Day 1). The salicylic acid created in this component of the experiment will be used to prepare acetylsalicylic mountain (aspirin) (Day 2). The aspirin should be very pure, so girlfriend will carry out a 2nd purification that the aspirin ~ above the third day.
Day 1: Hydrolysis that Methyl Salicylatecountless esters have familiar odors. Methyl salicylate, an ester obtained from the mix of salicylic acid and also methanol, is also known as the oil that wintergreen. Methyl salicylate was first isolated in pure form in 1843 by exploit from wintergreen plant (Gaultheria). It to be soon found that this compound had analgesic and antipyretic character virtually identical to the of salicylic acid when taken internally. This medicinal result probably results from the ease v which methyl salicylate is hydrolyzed to salicylic acid under the alkaline conditions found in the minister tract. Methyl salicylate deserve to be taken internally or took in through the skin, therefore its usage in some liniment preparations. When applied to the skin, that produces a mild burning or soothing sensation, which is probably because of the action of that phenolic hydroxyl group. Methyl salicylate additionally has a pleasant odor, and also it is offered as one extract for flavoring purposes. Esters deserve to be hydrolyzed into their carboxylic acid and also alcohol contents under one of two people acidic or basic conditions in the visibility of heat. In this experiment, methyl salicylate, one ester also known together oil the wintergreen because of that natural resource and odor, is treated through aqueous base and heated. Since, in our experiment, hydrolysis occurs in the presence of basic (instead of acid), the carboxylic acid and also phenolic -OH teams on salicylic acid are ionized and also this compound exists as the salt salt of salicylic acid, sodium salicylate. The reaction mixture is consequently acidifed utilizing sulfuric acid, i beg your pardon converts this anion into the totally protonated acid, salicylic acid. The alcohol is methanol. The salicylic acid, i m sorry is greatly insoluble, is a solid and can it is in isolated and also purified by crystallization. The chemical equation that describes this experiment is: As discussed above, the phenolic hydroxyl group, which is likewise acidic, would be ionized and also exist together the salt salt throughout the simple hydrolysis, similar to the carboxylic acid group, yet it is not shown ionized in this figure due to the fact that we are came to with the ester hydrolysis. As the following number shows, the phenolic -OH, and also the carboxylic acid group, will be protonated during the acidification step adhering to the enhancement of the sulfuric acid. The following figure shows what happens during acidification: The hydrolysis the methyl salicylate will be performed making use of the following setup.Obtain around 25 mL that freshly ready 5 M NaOH (or, alternatively, you can dissolve 5.0 g of sodium hydroxide pellets in 25 mL the water). Pour into a 100-mL round bottom flask (always use a funnel; never ever pour chemicals through a ground-glass opening).Add 7.5 g (0.050 mol; 50 mmol) the methyl salicylate (a liquid) to the 100-mL round-bottomed flask comprise the NaOH. (a white solid might form, however it will certainly dissolve quickly when the mixture is heated.)Add ~3-4 boiling stones to protect against bumping (which is the manufacturing of a large gas bubble as soon as heated) or uneven boiling. Attach a reflux condenser to the peak of the flask and also turn on the cooling water. warmth the reaction mixture to boiling using a heater mantel. Allow the mixture to reflux (with cooling) for about 20 minutes. The liquid mixture should be continually boiling for the entire reflux time. after ~ a 20 min reflux, deliver the reaction mixture to a 250-mL beaker. Add 50 mL of DI water come the reaction contents in her beaker.Either add a stirring bar or vigorously stirr the solution with a glass stirring rod together you include acid in the next step.Carefully include enough 3 M H2SO4 to make the systems acidic to litmus document (pHydroin paper) to a pH the 1. Note: the is best to include the acid slowly with stirring come mix the contents rather than simply pouring the acid right into the beacker. Stirring and including slowly should prevent sodium salicylate from becoming entrapped in the solid salicylic acid.You may need to add much more than 25 mL that 3 M sulfuric acid (for example, you will need much more than 20 mL simply to neutralize the NaOH provided in the reaction). Solid salicylic acid should form as the neutralization proceeds. After pHydroin record shows a pH of 1, add 1-2 mL much more of the 3M sulfuric acid to ensure all the salicylic acid precipitates. The mixture will certainly be acidic, yet too much acid will certainly not be a problem: Acid continues to be acid in acid!Cool the mixture in an ice-water bath to about 0oC. Permit beaker remain in the ice bucket for around 15 min while permitting the crystals come settle.The salicylic acid should must it is in a slurry prior to you carry out the filtration. So, if the heavy is not freely flowing in the beaker, include enough water so the the hard is suspended and also a fluid slurry appearance.Collect the crystals through vacuum filtration, using a Büchner funnel and also filter paper. The filtration deserve to be performed most easily by decanting off most of the supernatant liquid with the Büchner funnel before adding the mass of crystals. Closely wash the beaker with ice cold water, if necessary, to transfer all the crystals come the funnel. keep the salicylic mountain crystals in an evaporating dish or beaker in the drying oven until the following lab period. Since your gathered crystals native an mountain solution, friend cannot store your filter record with your chemical.
STOP and also STORE THIS component OF THE EXPERIMENT till THE following LAB PERIOD!
Day 2: Procedure for the preparation of aspirinonce the crystals room thoroughly dry, sweet them and determine the percent yield, based on the quantity of starting material. Remember, 1 mol of methyl salicylate yields 1 mol the salicylic acid). Recognize the melting suggest of her purified salicylic mountain (m.p. 159-160oC) and also compare it come a sample of pure salicylic acid from the stockroom. Aspirin is a trade name for acetylsalicylic acid, a typical analgesic. Acetylsalicylic mountain is an acetic acid ester derivative of salicylic acid. The earliest well-known uses the the drug have the right to be traced ago to the Greek doctor Hippocrates in the fifth century B.C. He offered powder extract from the bark of willows come treat pain and reduce fever. Salicin, the parent of the salicylate drug family, was successfully isolated in 1829 from willow bark. Sodium salicylate, a predecessor come aspirin, to be developed together with salicylic acid in 1875 together a pain reliever. Sodium salicylate was not often popular though, as it has actually a habit the irritating the stomach. However, in 1897, a man named Felix Hoffman changed the face of medicine forever. Hoffman was a German chemist working for Bayer. He had been using the usual pain reliever of the time, salt salicylate, to treat his father's arthritis. The sodium salicylate caused his father the exact same stomach problem it brought about other people, for this reason Felix decided to try and concoct a less acidic formula. His work brought about the synthetic of acetylsalicylic acid, or ASA. This soon became the pain killer of an option for physicians about the globe. Scientists never really understood the inner operations of the medicine however. It wasn't till the 1970's, once British pharmacologist john Vane, Ph.D. Began work on aspirin that people began to understand just how aspirin yes, really works. Vane and also his colleagues uncovered that aspirin inhibited the relax of a hormone favor substance dubbed prostaglandin. This chemical regulates details body functions, such together blood ship elasticity and changing the features of blood platelets. Thus have the right to aspirin influence blood clotting and ease inflammation. The reaction because that synthesis of acetylsalicylic acid is displayed in the following figure. Salicylic acid, prepared from the hydrolysis of methylsalicylate is reacted with acetic anhydride producing the ester product, acetylsalicylic acid. In a vault experiment, we have used the Fischer esterification reaction to develop isopentyl acetate indigenous an acid (acetic acid) and an alcohol (isopentyl alcohol). The existing experiment uses the carboxylic acid derivative, acetic anhydride, for ester formation. The advantage of using acetic anhydride is the you perform not create water which have the right to be provided for hydrolysis that the newly created ester. Focused sulfuric acid will certainly be used to keep everything in the protonated state. Acetic anhydride is the wanted acid derivative come synthesize aspirin commercially due to the fact that the acetic acid developed in this reaction (a reaction by-product) have the right to be used again, by converting it earlier into acetic anhydride. If girlfriend recovered much less than 3.5 g the salicylic acid, girlfriend will require to change the amounts of reagents supplied inthis protocol. However, if friend recovered at least 3.5 g salicylic acid, usage the quantities of reagents listed below (remember, if girlfriend recovered more than 3.5 g the salicylic acid, use only 3.5 g salicylic acid regardless of exactly how much you recovered). If girlfriend recovered less than 3.5 g salicylic acid, just proportion the amounts of the other reagents because that this reaction. begin the aspirin synthetic reaction: Preheat 60-90 mL the water in a 400-mL beaker come boiling. Place around 3.5 g that salicylic acid into a 125-mL Erlenmeyer flask (do no use an ext salicylic acid, also if friend isolated more)Add 3.5 mL that acetic anhydride (density is 1.08 g/mL) making use of a pipettor (if girlfriend reset the pipettor come a different value, please reset it back to the 3.5 mL value so other students don"t usage the wrong amount).Add around 4 or 5 drops of concentrated (18 M) sulfuric mountain
Thoroughly cool the flask to complete the early stage crystallization that aspirin. Remember that when a solution becomes cloudy, that is a solid forming and also this would be the crystals the aspirin girlfriend desire. If crystals are sluggish in forming, you might need to scrape the inside of the Erlenmeyer flask v a glass rod, i beg your pardon will rate up crystal development by seeding, or initializing the development of crystals. Collect your aspirin via vacuum filtration, and let air continue to be drawn over the solid for about 10 minute to evaporate many of the water surrounding the solid.
The aspirin product will be analyzed using HPLC (High pressure Liquid Chromatography). The HPLC resolves the aspirin from the salicylic acid. For your analysis, load out precisely 0.0100 grams the sample and also place in a clean test tube. To this check tube, add five mL methanol, and also swirl come dissolve aspirin. Then, include 5 mL Milli-Q water (ultra purified) to facilitate dissolving. This liquified material will certainly be given to one IA who will run your sample ~ above the HPLC and also give you a copy of the color layer analyzer of your crude aspirin.Characterization the aspirin by re-crystallization and solubility
Take about 2 grams of her slightly moist aspirin isolated over and add to a little beaker. Add either 5 mL of methanol or 5 mL the acetone and gently swirl come dissolve the solid. You may need to warm slightly, yet do no boil the mixture. Every one of the aspirin should dissolve in the heat solvent. Eliminate the manufacturer containing the aspirin-solvent mixture and also let the cool to room temperature ~ above the bench. When it is about room temperature (the beaker will certainly feel slightly cool to the touch), location the beaker in an ice bucket to proceed to produce crystals. After about 15 minutes on ice, collect by vacuum filtration your crystals (do not use water to wet the filter paper, but use the exact same solvent come wet the filter file prior come collecting crystals).
Let the vacuum proceed to be drawn through the Buchner funnel for around 15 minutes to completely evaporate the solvent.
At this point, your filter record and her crystals have to be dry. Weigh your sample to recognize your yield of re-crystalized aspirin. Because that HPLC analysis of your re-crystallized aspirin, weigh out around 0.0100 grams of your re-crystalized aspirin and include 5 mL of the anhydrous methanol, dissolve and also then add 5 mL Mili-Q water to dissolve her solid. Slim warming must not it is in necessary.
Do a yield, percent yield, and melt temp of your re-crystallized aspirin. Be certain to have actually your aspirin samples analyzed via HPLC.
Caution: Aspirin decomposes in boil water (therefore, execute not boil the aspirin) or when liquified in solutions of alkali hydroxides and carbonates. Not natural salts of acetylsalicylic acid space soluble in water (especially the Calcium salt, yet are decomposed quickly.An alternate re-crystallization procedure might include among the following options:The purpose of re-crystallization is to eliminate contaminating chemicals, such as salts. So, even if you carry out not fully dissolve all your aspirin, you might still impact a purification by adding a specific amount the water. After including some water (e.g., approximately 100 mL water), heat the mixture increase to50-60oC and let as lot aspirin dissolve as possible. Then, cool the mixture and let the crystals form, also though not all the heavy may have gone solution. This an approach effectively washes the crystals and lets the contaminants obtain diluted into the solvent. After cooling, collect the crystals by vacuum filtration.You can take advantage of the high solubility in one solvent and the reduced solubility in another. Because that example, if her solid dissolves quickly in ethanol, however not well in water (check the solubilities above), very first dissolve your solid in as tiny ethanol together possible, maybe at a slightly elevated temperature. Then, include a large excess that water (e.g., 100 mL the water), and also let her sample stand on ice cream for 10-15 min. Collection the crystals together normal.
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Analysis of product.
What is the productivity of dried aspirin? What is the percent yield? What is the melt point? (The crystals may have a broad melting range, native 125-138oC, since of potential of decomposition. The use of a preheated melting point maker (heated to around 110oC) will help to minimization this decomposition. Why carry out you think this could help prevent decomposition?)Chemicals, Reagents, and also Supplies link MW amount mmol mp bp density ηD msds Methyl salicylate 152.15 6.4 mL (7.5 g) (use pipettor) 49.3 -8.6 223.3 1.184 msds Salicylic acid 138.12 3.5 g 25.3 159 211 1.44 msds Acetyl salicylic acid (aspirin) 180.16 135 140 1.35 msds Acetic anhydride 102.09 3.5 ml (use pipettor) -73.1 139.9 1.08 1.389 msds NaOH (5 M) 40.0 25 mL 125 msds H2SO4 (6 M) because that Day 1 98.0 8-10 mL msds H2SO4 (18 M) because that Day 2 98.0 a few drops msds