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11 Dec 2019

In a recrystallization, the crystals do not always form spontaneously after cooling, even though the solution is supersaturated. Which of the following will help crystals form? More than one answer may be correct.

1. Scrape the inside of the Erlenmeyer flask with a glass rod below the surface of the solvent.

2. Add a scrap of paper to nucleate the crystals.

3. Add some crystals of the compound you are trying to crystallize.

4. Add some crystals of any kind.

5. Scrape the outside of the Erlenmeyer flask with a glass rod.

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Exp. 11 (2 meetings): Synthesis of Aspirin and Melting Point Determination

1. What is the melting point range of your aspirin sample?

2. What were the results of your FeCl3 tests when you compared the aspirin you made to the commercial aspirin?

3. Do the results of your melting point determination agree with the results from your FeCl3 test? Explain.

POST-LAB QUESTIONS:

1. Give two physical properties you observed in your crude (unpurified) aspirin sample.

2. If the theoretical yield of a reaction was calculated to be 3.11g and the actual yield was 2.65g, what was the percent yield for the reaction? Show formula and all work.

3. If a melting point range is greater than 3o C, such as 119.5o C to 125.8o C, what can you say about the sample?

Coution! The preporation of aspirin involves the use of two hozardous materials- concentrated sulfuric ocid anhydride, These chemicols should be in Hood 7-do not remove from Hood 7 SYNTHESIS OF ASPIRIN (acetylsalicylic acid): 1. Set up a hot water bath (boiling) using a 400mL beaker filled with tap water on a hot plate water you will 2. Using a metal bowl from the drawers under the hoods, start an ice water bath so the i 3. Using a top loading balance, mass out approximately 2.50 g of salicylic acid. If you use a di 4 s, start an ice water bath so the ice-cold need later will be cool enough, You will also use this as an ice bath sposable weight beat mass (vou will need it be sure to tare/re-zero the weigh boat before adding the salicylic acid Record the precise mass ( to calculate the % yield) in the data table Place the salicylic acid in a clean and dry 125 ml Erlenmeyer flask me concentrated H2saa and acetic anhydridew remain in Hood 7. Using cylinder, carefuly altern Place the tethe%acid inin thedatatable125 mLErien ever tas 4 a clean and dry 10 mL graduated 5. to the flask 6 Add 7:2 dreps of concentrated HsQ4 (sulfuric acid) to the (sulfuric acid) to the flask mixture thoroughly and place Erienmeyer into the hot water bath if the water is boiling. Take acid remains dissolved (no solid is present) the hot water bath and allow to cool for 3.5 minutes (you may see white solid begin to Gently swirl the care to ensure that the reaction flask does 7. r not tip to allow water in it. If this happens, you will need to start Swirl frequently or stir with a glass rod to ensure the solid salicylic and continue heating in boiling bath for 10 minutes. Remove the flask from the hot water bath and allow to cool for 3-5 minutes (you may see white crystallize). 8. 9. Calculate the theoretical yield of the product (1 mole salicylic acid 135g. 1 mole of acetyl salicylic acid 180g). Show 38g SA 10. Tilt the mouth of the ask away from Vou and add approximately S ml of ICE CoLD water to the flask After you've decomposed the excess acetic anbydride, add 40 ml of ICE COLD water to the flask, swirl, and let the flask sit at to room temperature, undisturbed, for approximately 3-5 minutes (this allows the aspirin crystals to grow). Aspirin crystals should form as the flask cools Observations- What do you see in the flask: watey 11. Gently lower the flask containing your aspirin crystals into the CE BATH to cool the liquid so more aspirin crystals can crystallize out of the solution (do not allow any additional water inside the flask). Let the crystals continue to form in the ice water bath for approximately 10 more minutes ust ice cout vatemx roughly, and place the peskeratnettndturbed ntl erystal 12. While waiting for all of the aspirin to crystallize out of the solution, record the mass of a piece of filter paper (size: 70 mm). You will use this piece of flter paper with the Buchner funnel /vacuum filtration to isolate your aspirin crystals Collect Buchner funnel, black or grey adapter to achieve a good seal, vacuum hose, filter flask, ring stand, and your massed filter paper and assemble next to a sink with an aspirator adapter V02 3 V 02 3

Preparation of acetyl salicyclic acid (Aspirin) post-lab questions

1.)At the end of the reaction, you were asked to add ice-cold water to the reaction mixture. What do you think is the reason for this? Explain with chemical equations.

2.)How would the % yield of aspirin be changed if the final rinse of the solid product on the filter paper was done with warm water instead of ice-cold water?

3.)If you run a thin-layer chromatography for a mixture containing salicylic acid and aspirin using a 1:1 solvent mixture of ethyl acetate and hexane, which compound do you think would have more R_f value. Explain why? Bring in the structural features in your explanation.

summary Procedure of lab we did:

- Place approximately 0.300 g of salicylic acid in a tared empty 5 mL conical reaction vial. Record the actual weight of salicylic acid used. Using automatic pipet, add 0.8 mL of acetic anhydride (acetic anhydride vapors are very irritating-handle it carefully, in the hood). Add 2-3 drops of concentrated sulfuric acid using a dropper.

-Clamp the assembly so that the vial is partially submerged in the hot water. Turn on the magnetic stirrer. Once the water bath starts boiling, start timing the reaction. When the mixture has been allowed to react at 100 oC (the temperature of boiling water) for 15 minutes, you can consider the reaction to be complete. During the heating time, take about 20 mL of deionized water in a flask and chill it in an ice-water bath.

- After the reaction has gone on for 15 minutes, add very cautiously, drop by drop, 1 mL of deionized water to the reaction vial. At this point you should have a solution in your reaction vial. Remove the reaction vial form the hot water bath, add another 1-2 mL of DI water and let it stand at room temperature for few minutes. Then, detach the air condenser carefully and remove spin vane with forceps. Place the vial in a beaker and cool down to RT. During this time, the aspirin may begin crystallizing. If not, scratch the walls of the vial with a glass rod. Then, cool the vial in an ice-water bath.

- When the vial appears full of crystals, add about 3-4 mL of ice-cold DI water. Filter the aspirin using vacuum filtration (use Hirsch funnel). Leave the filtration setup in place for few minutes-this will draw air through the sample and will help dry aspirin.

Recrystallization of Aspirin:

- Transfer the rest of the crude aspirin to a 25 mL Erlenmeyer flask and do recrystallization using ethanol.

Purity of Aspirin:

- Using the melting point apparatus, determine the melting point of your crude aspirin and the recrystallized aspirin.

- To do FeCl3 test, get 4 test tubes. Place 1 mL of ethanol and 2 drops of 1% FeCl3 solution in each test tube. Add few crystals of salicylic acid to one test tube. Add few crystals of your crude aspirin product to the second test tube. In the thirst test tube, place a few crystals of your recrystallized aspirin. The fourth test tube will be your âblankâ. Shake each of the test tubes and record your observations.

Include a hand drawn reaction mechanism for the reaction that was performed

for the synthesis of aspirin. A generalized mechanism will not be accepted. The mechanism should show the flow of electrons via arrow pushing in the correct direction.

DIRECTIONS Acetie anhydrite can cuuse severe dis very haomful ir Inhaled.nnd It renets a hoodi avoid contact with do n it nway from water Sulfurle ncid causes chemleat burns that cnn eyes. Wenr gloves and nvold contact. h the iuld,do not breathe its vnpurs, and bee iloroform is harmful ir ininled or usorted eeted human earcinogen. Avoid contact with the ii, d and it is a do not breathe its vapors. e Standard Scale Reaction. Under the hood, add 5.0 mL of ncetic anhydride to 15. of salicylic acid in a dry 125-m. Erlenmeyer lask. Add 3 4 drop centrated sulfuric acid. and stir or swirl [OP-10 the r OP-7 the mixture in a 45-50 C water bath with frequent swirling or netic stirring until the salicylic acid dissolves, and then for about 5 minutes more. Let the flask stand at room temperature until crystallization begins lt no product has precipitated when the solution is near room temperature resulting mixture. THeat induce crystallization by scratching the wall of the lask at the surface of the solution with a glass stirring rod, or by adding a few seed crystals of pure as- pirin. When a heavy precipitate has formed. stir in 30 mL of cold water and break up any lumps with a lat-bottomed stirring rod. Cool the mixture in an ice/water bath until crystallization is complete. Separation. Separate the aspirin from the reaction mixture by vacuum filtration [OP-16] and wash it on the filter [OP-26al with several portions of ice-cold water. using a small amount of the wash water for transfer. Save about 20 mg of the crude product in a clean, labeled test tube for analysis, and transfer the rest to a beaker Purification. Recrystallize [OP-28] the aspirin from an ethanol/water misx ture, using the following procedure to reduce the likelihood of hydrolysis st Dissolve the aspirin in the minimum volume of boiling 95% ethanol and add another 1 mL of ethanol, measuring the total volume of ethanol used Add twice that volume of warm (60 C) water to the solution while it is still at the boiling point, and swirl to mix.If any precipitate forms, heat the solu tion gently until it is clear, but do not boil it. Let it cool slowly to room tem perature, induce crystallization if necessary, and cool it in an ice/water bat until crystallization is complete. Collect the aspirin by vacuum filtratio OP-16], and wash it on the filter [OP-26a] with ice-cold water. Save anothe small sample of the aspirin in a clean, labeled test tube for analysis. D [OP-26b) and weigh the remaining aspirin. Analysis. Place about 20 mg of salicylic acid in a clean, labeled test tub then dissolve each reserved aspirin sample and the salicylic acid in 1 ml o 95% ethanol. The aspirin samples need not be completely dry. Add a drop

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