Objectives

Many normally arising chemicals have the right to be provided isolated and provided to make various other compounds. Methyl salicylate is a normally developing compound that we will certainly use to develop salicylic acid, which will then be used to make the wonder drug aspirin (acetylsalicylic acid). This is not the source of salicylic acid in the commercial synthesis of aspirin, however it is, neverthemuch less, a great one for laboratory use. Two different chemical approaches will certainly be employed. First is hydrolysis, which is the breaking of a bond via water. Esters are fairly easily hydrolyzed right into their two beginning components, an acid and an alcohol. Then, we perform an ester synthesis for the development of aspirin. Equilibrium favors hydrolysis, however using acetic anhydride as the acid resource stays clear of this backward reactivity, because water is not produced throughout ester formation. Both salicylic acid and also aspirin are conveniently isolated.

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Background

Methyl salicylate (an ester) have the right to be hydrolyzed to create salicylic acid. The two different functional teams on the fragrant ring are used in this lab. First, the complimentary carboxylic acid group will be created once we hydrolyze the methyl salicylate. Methanol is the alcohol which is released by hydrolysis. 2nd, the hydroxyl group on salicylic acid will certainly be offered in ester formation to develop aspirin. When we percreated an ester synthesis formerly, we took one-of-a-kind precautions to prevent water from being created (we contained a dessicant in the reactivity mixture and also had a drying tube affixed on peak of the reflux column). Acetic anhydride will be used in this experiment so that as soon as ester is developed, water is not created. As an outcome, the thermodynamic equilibrium will currently be for the formation of an ester instead of its hydrolysis. Before proceeding through the experiment you have to testimonial numerous items. First, you need to be familiar via the ester practical group. Esters are created once an acid and an alcohol integrate. You need to be able to quickly determine an ester by looking at the structural formula. Tright here are just three forms of compounds which have an oxygen located in between 2 carbons. These are ethers, esters and also acid anhydrides. Can you recognize the differences? 2nd, we will certainly percreate a hydrolysis reactivity. Hydrolysis occurs when water is provided to break a bond. Hydrolysis have the right to take place in either standard or acidic problems. We will learn later the actual mechanisms, but in both instances we produce one chemical which is an alcohol and also the other chemical will certainly be a carboxylic acid once esters are hydrolyzed. Third, we will produce an ester. It must be noted that ester development cannot take place in the visibility of base, only acid. Throughout the first day of this lab, we will produce salicylic acid. This acid will then be provided to make aspirin. The synthesis of aspirin is a multi-billion dollar a year chemical. While salicylic acid as some therapuetic worth, it is not as effective as aspirin in reducing inflammation and other prevalent clinical conditions for which aspirin can be offered. Aspirin is component of a big team of chemicals classified as Non-Steriodal Anti-Inflammatory Drugs (NSAIDS).

Procedure

This experiment is created of two components. The first involves the hydrolysis of methyl salicylate in order to create salicylic acid (Day 1). The salicylic acid produced in this component of the experiment will be offered to prepare acetylsalicylic acid (aspirin) (Day 2). The aspirin should be incredibly pure, so you will certainly do a second purification of the aspirin on the third day.

Day 1: Hydrolysis of Methyl Salicylate

Many esters have actually familiar odors. Methyl salicylate, an ester acquired from the combicountry of salicylic acid and methanol, is additionally recognized as the oil of wintergreen. Methyl salicylate was initially isolated in pure form in 1843 by extractivity from wintergreen plant (Gaultheria). It was quickly found that this compound had actually analgesic and also antipyretic character practically similar to that of salicylic acid once taken internally. This medicinal result most likely results from the ease with which methyl salicylate is hydrolyzed to salicylic acid under the alkaline problems discovered in the intestinal tract. Methyl salicylate have the right to be taken internally or absorbed via the skin, hence its usage in some liniment preparations. When used to the skin, it produces a mild burning or soopoint sensation, which is more than likely because of the action of its phenolic hydroxyl group. Methyl salicylate also has actually a pleasant odor, and it is provided as an extract for flavoring functions. Esters can be hydrolyzed right into their carboxylic acid and also alcohol components under either acidic or standard conditions in the presence of warm. In this experiment, methyl salicylate, an ester additionally known as oil of wintergreen bereason of its organic source and also odor, is treated through aqueous base and heated. Because, in our experiment, hydrolysis occurs in the presence of base (instead of acid), the carboxylic acid and also phenolic -OH teams on salicylic acid are ionized and this compound exists as the sodium salt of salicylic acid, sodium salicylate. The reactivity mixture is ultimately acidifed making use of sulfuric acid, which converts this anion right into the completely protonated acid, salicylic acid. The alcohol is methanol. The salicylic acid, which is mostly insoluble, is a solid and can be isolated and purified by crystallization. The chemical equation that defines this experiment is: As stated over, the phenolic hydroxyl team, which is additionally acidic, would be ionized and exist as the sodium salt throughout the basic hydrolysis, simply choose the carboxylic acid group, however it is not presented ionized in this figure because we are involved via the ester hydrolysis. As the complying with figure reflects, the phenolic -OH, and the carboxylic acid team, will be protonated in the time of the acidification action following the addition of the sulfuric acid. The complying with figure reflects what happens throughout acidification: The hydrolysis of methyl salicylate will certainly be percreated using the complying with setup.Obtain about 25 mL of freshly prepared 5 M NaOH (or, alternatively, you can dissolve 5.0 g of sodium hydroxide pellets in 25 mL of water). Pour right into a 100-mL round bottom flask (constantly use a funnel; never before pour chemicals via a ground-glass opening).Add 7.5 g (0.050 mol; 50 mmol) of methyl salicylate (a liquid) to the 100-mL round-bottomed flask containing the NaOH. (a white solid might create, yet it will certainly disdeal with conveniently once the mixture is heated.)Add ~3-4 boiling stones to prevent bumping (which is the manufacturing of a big gas bubble when heated) or uneven boiling. Attach a reflux condenser to the peak of the flask and rotate on the cooling water. Heat the reactivity mixture to boiling making use of a heating mantel. Allow the mixture to reflux (through cooling) for around 20 minutes. The liquid mixture need to be continually boiling for the whole reflux time. After a 20 min reflux, transport the reactivity mixture to a 250-mL beaker. Add 50 mL of DI water to the reactivity contents in your beaker.Either add a stirring bar or vigorously stirr the solution via a glass stirring rod as you add acid in the next action.Caretotally add sufficient 3 M H2SO4 to make the solution acidic to litmus paper (pHydroin paper) to a pH of 1. Note: It is finest to include the acid progressively via stirring to mix the contents fairly than simply putting the acid into the beacker. Stirring and also including progressively must proccasion sodium salicylate from coming to be entrapped in the solid salicylic acid.You might need to include even more than 25 mL of 3 M sulfuric acid (for example, you will certainly require more than 20 mL simply to neutralize the NaOH supplied in the reaction). Solid salicylic acid must develop as the neutralization proceeds. After pHydroin paper shows a pH of 1, add 1-2 mL more of the 3M sulfuric acid to ensure all the salicylic acid precipitates. The mixture will be acidic, yet as well much acid will not be a problem: Acid continues to be acid in acid!Cool the mixture in an ice-water bath to around 0oC. Let beaker continue to be in the ice bucket for about 15 min while allowing the crystals to settle.The salicylic acid should need to be a slurry before you perform the filtration. So, if the solid is not easily flowing in the beaker, add sufficient water so that the solid is suspended and a liquid slurry appearance.Collect the crystals by vacuum filtration, using a Büchner funnel and also filter paper. The filtration can be performed a lot of conveniently by decanting off many of the supernatant liquid with the Büchner funnel prior to including the mass of crystals. Carefully wash the beaker with ice cold water, if necessary, to move all the crystals to the funnel. Store the salicylic acid crystals in an evaporating dish or beaker in the drying oven until the next lab period. Due to the fact that your collected crystals from an acid solution, you cannot store your filter paper with your chemical.

STOP AND STORE THIS PART OF THE EXPERIMENT UNTIL THE NEXT LAB PERIOD!

Day 2: Procedure for the preparation of aspirin

When the crystals are thoaround dry, weigh them and recognize the percent yield, based on the amount of starting product. Remember, 1 mol of methyl salicylate yields 1 mol of salicylic acid). Determine the melting allude of your purified salicylic acid (m.p. 159-160oC) and also compare it to a sample of pure salicylic acid from the stockroom. Aspirin is a profession name for acetylsalicylic acid, a prevalent analgesic. Acetylsalicylic acid is an acetic acid ester derivative of salicylic acid. The earliest recognized uses of the drug have the right to be traced back to the Greek medical professional Hippocrates in the fifth century B.C. He offered powder extracted from the bark of willows to treat pain and also minimize fever before. Salicin, the parent of the salicylate drug family members, was properly isolated in 1829 from willow bark. Sodium salicylate, a predecessor to aspirin, was developed along with salicylic acid in 1875 as a pain reliever. Sodium salicylate was not regularly famous though, as it has actually a habit of irritating the stomach. However, in 1897, a guy named Felix Hoffmale changed the challenge of medication forever. Hoffguy was a Gerguy chemist working for Bayer. He had been using the widespread pain reliever before of the moment, sodium salicylate, to treat his father's arthritis. The sodium salicylate caused his father the exact same stomach trouble it resulted in other civilization, so Felix determined to try and also concoct a much less acidic formula. His work led to the synthesis of acetylsalicylic acid, or ASA. This soon ended up being the pain killer of option for medical professionals roughly the globe. Scientists never really understood the inner workings of the drug but. It wasn't till the 1970's, once British pharmacologist John Vane, Ph.D. began occupational on aspirin that people started to understand exactly how aspirin really works. Vane and also his colleagues discovered that aspirin inhibited the release of a hormone like substance dubbed prostaglandin. This chemical regulates specific body attributes, such as blood vessel elasticity and altering the attributes of blood platelets. Therefore have the right to aspirin influence blood clotting and also ease inflammation. The reactivity for synthesis of acetylsalicylic acid is presented in the complying with number. Salicylic acid, all set from the hydrolysis of methylsalicylate is reacted through acetic anhydride developing the ester product, acetylsalicylic acid. In a previous experiment, we have offered the Fischer esterification reactivity to create isopentyl acetate from an acid (acetic acid) and an alcohol (isopentyl alcohol). The current experiment offers the carboxylic acid derivative, acetic anhydride, for ester formation. The advantage of using acetic anhydride is that you do not create water which can be offered for hydrolysis of the recently created ester. Concentrated sulfuric acid will certainly be supplied to keep everything in the protonated state. Acetic anhydride is the preferred acid derivative to synthedimension aspirin commercially because the acetic acid created in this reaction (a reactivity by-product) have the right to be used aacquire, by converting it back into acetic anhydride. If you reextended less than 3.5 g of salicylic acid, you will have to adjust the amounts of reagents provided inthis protocol. However, if you respanned at least 3.5 g salicylic acid, usage the quantities of reagents provided listed below (remember, if you reextended even more than 3.5 g of salicylic acid, usage just 3.5 g salicylic acid regardless of how much you recovered). If you respanned much less than 3.5 g salicylic acid, just proportion the amounts of the various other reagents for this reactivity. Initiate the aspirin synthesis reaction: Preheat 60-90 mL of water in a 400-mL beaker to boiling. Place around 3.5 g of salicylic acid right into a 125-mL Erlenmeyer flask (carry out no usage even more salicylic acid, even if you isolated more)Add 3.5 mL of acetic anhydride (thickness is 1.08 g/mL) making use of a pipettor (if you recollection the pipettor to a various worth, please recollection it ago to the 3.5 mL value so various other students don"t usage the wrong amount).Add about 4 or 5 drops of focused (18 M) sulfuric acid to the mixture (some warm may be generated). This addition of acid allows the carbonyl carbon of acetic anhydride to be even more electrophilic.Heat the flask containing your reactants by placing it right into a beaker of boiling water for five or 6 minutes. Stir the mixture by gently swirling the flask. Throughout this time, the solid need to disfix completely. Isolation of aspirin Remove the flask from the boiling water bath, and add 15 mL of ice water to it. (The ice hydrolyzes the unreacted anhydride and keeps the mixture cool. Can you compose the equation of this hydrolysis reaction?)

Thoabout cool the flask to complete the initial crystallization of aspirin. Remember that when a solution becomes cloudy, that is a solid forming and this would be the crystals of aspirin you desire. If crystals are sluggish in creating, you might have to scratch the inside of the Erlenmeyer flask with a glass rod, which will certainly rate up crystal formation by seeding, or initializing the development of crystals. Collect your aspirin via vacuum filtration, and let air proceed to be drawn over the solid for around 10 minutes to evapoprice most of the water bordering the solid.

The aspirin product will certainly be analyzed making use of HPLC (High Prescertain Liquid Chromatography). The HPLC resolves the aspirin from the salicylic acid. For your analysis, weight out specifically 0.0100 grams of sample and area in a clean test tube. To this test tube, include five mL methanol, and also swirl to dissolve aspirin. Then, include 5 mL Milli-Q water (ultra purified) to facilitate disresolving. This dissolved material will certainly be provided to an IA that will certainly run your sample on the HPLC and also offer you a copy of the chromatogram of your crude aspirin.

Characterization of aspirin by re-crystallization and also solubility

Take about 2 grams of your slightly moist aspirin isolated over and add to a tiny beaker. Add either 5 mL of methanol or 5 mL of acetone and gently swirl to disdeal with the solid. You might need to heat slightly, yet carry out not boil the mixture. All of the aspirin must disdeal with in the warm solvent. Remove the beaker containing the aspirin-solvent mixture and also let it cool to room temperature on the bench. When it is around 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 usage water to wet the filter paper, however usage the same solvent to wet the filter paper before collecting crystals).

Let the vacuum proceed to be drawn via the Buchner funnel for around 15 minutes to thoroughly evaporate the solvent.

At this allude, your filter paper and your crystals need to be dry. Weigh your sample to recognize your yield of re-crystalized aspirin. For HPLC analysis of your re-crystallized aspirin, weigh out around 0.0100 grams of your re-crystalized aspirin and add 5 mL of the anhydrous methanol, disresolve and then include 5 mL Mili-Q water to disresolve your solid. Slight warming have to not be crucial.

Do a yield, percent yield, and melt temp of your re-crystallized aspirin. Be certain to have actually your aspirin samples analyzed using HPLC.

Caution: Aspirin decomposes in boiling water (therefore, execute not boil the aspirin) or when dissolved in services of alkali hydroxides and also carbonates. Inorganic salts of acetylsalicylic acid are soluble in water (especially the Calcium salt, however are dewritten conveniently.

An alternative re-crystallization procedure might encompass one of the following options:The purpose of re-crystallization is to eliminate contaminating chemicals, such as salts. So, also if you do not completely disresolve all your aspirin, you can still impact a purification by including a specific amount of water. After adding some water (e.g., up to 100 mL water), heat the mixture up to50-60oC and also let as a lot aspirin disresolve as feasible. Then, cool the mixture and also let the crystals form, also though not all the solid may have gone solution. This approach properly washes the crystals and lets the contaminants obtain diluted into the solvent. After cooling, collect the crystals by vacuum filtration.You can take benefit of the high solubility in one solvent and also the lower solubility in one more. For example, if your solid dissolves conveniently in ethanol, but not well in water (examine the solubilities above), initially disdeal with your solid in as little ethanol as possible, maybe at a slightly elevated temperature. Then, include a big excess of water (e.g., 100 mL of water), and let your sample stand also on ice for 10-15 min. Collect the crystals as normal.

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Analysis of product.

What is the yield of dry aspirin? What is the percent yield? What is the melt point? (The crystals may have actually a broad melting range, from 125-138oC, bereason of potential of decomplace. The use of a preheated melting point device (heated to about 110oC) will certainly assist to minimize this decomposition. Why do you think this could aid proccasion decomposition?)

Chemicals, Reagents, and also Supplies Compound 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 (usage pipettor) -73.1 139.9 1.08 1.389 msds NaOH (5 M) 40.0 25 mL 125 msds H2SO4 (6 M) for Day 1 98.0 8-10 mL msds H2SO4 (18 M) for Day 2 98.0 a couple of drops msds Compound g/mol grams or mL 10-3 mol oC oC g/mL ηD msds