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Experiment 8 Report

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Experiment 8 (2 weeks) (ASA) Aspirin Purpose The purpose of this experiment was to study and create a simple esterification reaction in order to produce acetylsalicylic acid (aspirin). This crude salicylate will be further analyzed to identify its purity.

Introduction A wide variety of esters can be formed through the addition of numerous different “R” functional groups. In this lab, the production of a specific ester from a process known as esterification will occur. This type of reaction ensues when a carboxylic group of acetic acid reacts with the hydroxyl group (OH -) of salicylic acid in order to make acetylsalicylic acid or more commonly known as aspirin (1). Aspirin is a commonly used drug for treatment of pain and fever due to various causes as it has both anti-inflammatory and antipyretic effects (2). The equation of the formation of aspirin is found below

C7H6O3(s) + C4H6O3(aq)

C9H8O4(s) + C2H3O2(aq)

In the first part of this lab, a catalyst (sulphuric acid) will be used to speed up the reaction. The esterification will occur as a result of heated carboxylic acids with alcohols. As this reaction is not reversible, more aspirin will be produced. In the second part of the lab, the crude product made from synthesis, will be recrystallized in water. Once dissolved, the product will be placed to dry in the vacuum filter. The purity will thus be easier to determine as there will be more of the desired product, will less impurities as well as any interfering substances. The melting point of the synthesized ASA as well as the recrystallized will be compared in order to determine which one is pure. It will be fairly simple to determine as the presence of more impurities results in a lower melting point.

Procedure Part I Synthesis 1. Set up the fume snorkel over the hot plate and prepare a hot-water bath (60-70oC) in a 600 mL beaker. 2. Prepare two ice-water baths in 600 mL beakers. Fill a 150 mL beaker with 90 mL of RO water and place it in one ice-water bath. 3. Weigh 5 g of salicylic acid into a 250 mL Erlenmeyer flask and dispense 7 mL of acetic anhydride directly into the 250 mL flask. Swirl to mix contents. 4. Add 8 drops of concentrate H2SO4 to the flask and swirl again. Take the flask and gently place it into the hot-water bath. (Note: Do not heat over 70 oC or the crystals will re-dissolve)

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5. Swirl the flask gently and after 7 minutes of heating, place the flask containing the crystals on the bench. 6. Cool the flask to room temperature and let the crystals grow. 7. Place the flask into the ice-water bath while breaking up the crystals with a glass stir rod. For further removal of any unreacted acetic anhydride, add 20 mL of the pre-cooled RO water to the flask. 8. Using the vacuum filtration system, collect the ASA crystals while gently washing them with water. 9. After the crystals are washed three times with ice-cold RO water, weigh a clean watch glass with the crystals to record its mass. 10. Place the crystals in the over to dry for approximately 10 minutes. At the end, record the mass of the product. Wait 5 minutes and weigh the sample again. Note if there is any change. *For more detailed steps, refer to page 103-104 of the First Year Laboratory Chemistry Manual. Part II Recrystallization 1. Weigh 1 g of the crude ASA product into a 150 mL beaker. 2. Boil 30-35 mL of RO water in a 50 mL beaker on the hot plate while setting it at a rotational speed of 200 rpm. 3. Use tongs to pour approximately 10 mL of the boiler water into the beaker of crude ASA, place the beaker with the product on the hot plate. Swirl the beaker gently to dissolve the product, 4. As soon as the ASA dissolved, cover the beaker with a watch glass and place it on the lab bench while allowing the solution to cool to room temperature. 5. Prepare two 600 mL ice-water baths and place a 150 mL beaker filled with 30 mL of RO water into one of the ice-baths. 6. Place the beaker with the product into the other ice-water bath for approximately 5 minutes. 7. Use the vacuum filtration system to dry the crystals. Weigh the total mass of the product, watch glass and filter paper. 8. Dry the crystals in the over for 15 minutes and weigh the crystals again. 9. Using the Mel-temp apparatus, compare the melting point of the product of the crude and recrystallized ASA. Record the values.

Observations A number of things were observed, particularly in regard to the odour of the product. As the compounds were mixed together and heated on the hot plate, it produced a smell similar to vinegar however the mixture was overall colourless. The smell was extremely harsh and pungent. When the acetic anhydride and the salicylic acid were mixed together, the liquid presented was off-white and fairly opaque. While boiling the flask, the temperature was maintained at a steady heat and it was fairly easy to keep it a 68.4 o C. It was apparent that the crystals formed within 3 minutes of being boiled, which was surprisingly

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quick. As they began to crystallize, they appeared to arrange themselves on the inner wall of the flask, similarly to icicles on a window. While crushing the crystals with a glass stir rod, it was noted that the small crystals were quite difficult to move around, thus extra force had to be exerted to complete this step as well as the addition of more water to the flask to facilitate this task. During the filtration process, large clumps of crystals were poured onto the filter paper resulting in the need to further break them apart. However, at the end of the process, the dried product appeared white and fine. After 10 minutes in the oven, both masses were compared and a slight decrease in weight was observed. During part two of the lab, the crude product presented more difficulty to dissolve as it the product appeared extremely clumpy. However, when cooled, the crystals formed significantly quick. After the recrystallized product was filtered, weighed, placed in the oven, then weighed once again, the same decrease in mass was noticed as seen in part one of the lab. When observing the melting point of the crude and recrystallized product, it was evident that the crude product had a lower melting point.

Questions Part I Synthesis 1. Calculate the theoretical yield of aspirin based on the number of moles of salicylic acid that you used. In order to calculate the theoretical yield of aspirin the balanced chemical equation is needed.

C7H6O3(s) + C4H6O3(aq)

C9H8O4(s) + C2H3O2(aq)

Number of moles of salicylic acid: n=m/M =

5.03 g 138.121 g/mol

= 0.0364 mol of salicylic acid

C7H6O3(s)

+.

C4H6O3(aq)

C9H8O4(s)

m (g)

5.03

6.56

M (g/mol)

138.121

180.16

n (mol)

0.0364

0.0364

The theoretical yield is calculate as followed: C7H6O3(s) to C9H8O4(s) mole ratio = 1:1 Molar mass of aspirin = 180.16 g/mol (3) =

0.0364 (1 / 1 )(180.16 )/ 1

+

C2H3O2(aq)

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= 6.56 g In essence the theoretical yield of aspirin is 6.56 g. 2. Calculate the percent yield of your crude product.

% yield of crude=

Actual crude yield x 100 % theoretical yield

Actual yield = 51.83-47.49 = 4.34 g

percent yield=

4.34 ×100=66 % 6.56

Thus, the percent yield of the crude product is 66.2%. Part II Recrystallization 3. Estimate the purity of the crude product using the ratio of the mass of recrystallized product to the mass of the crude product (assume that your recrystallized product is 100% pure). What can you say about the percent yield calculated in the Part I?

% purity= =

Mass pure x 100 % Massimpure

0.68 x 100=68 % 1.00

Thus, the estimated purity of the crude product, as shown above is 68%. The percent yield was extremely similar to the purity of crude product in part two of the lab. It is fair to conclude that 68% of the sample was pure product. 4. Compare the melting point range of your crude ASA lower than that of your recrystallized ASA. Discuss any similarity and differences.

The melting point of the crude aspirin is noticeably lower than that of the recrystallized aspirin as a result of the impurities contained within the product. The foreign impurities affect and lower the intermolecular forces of attraction between molecules resulting in “melting point depression”. This interruption in the crystalline solid, disrupts the lattice structure making it less stable. This loss of stability results in a smaller amount of energy required in order to melt the solid. This is why the crude product had a melting point range of 98-104.9 oC while the recrystallized aspirin has a melting point range of 129.7-130.2 oC. 5. List 3 possible systematic errors that you may have encountered in the lab and explain how they would have affected your final outcome. A numerous amount of systematic errors could have occurred throughout the experiment. To start off, it is likely that the filter paper used in the vacuum filtration system may have endured a hole within it which would skew the filtration of the product and thus its final yield. It is also possible that there was faulty equipment used such as a poorly calibrated scale or in other words, the analytical

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balance may not have been tared every time it was used which would lead to uncertainties of mass. Finally, the amount of liquids needed to fill up a beaker or flask may have been inaccurate due to the imprecision of human eye, leading to incorrect readings of measurement.

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References 1. Queen’s Chemistry: First-Year Laboratory Manual Chemistry 112. Kingston: Queen’s University. 2017-2018. Print. 2.

“Aspirin.” DrugBank, www.drugbank.ca/drugs/DB00945.

“Molar Mass of C9H8O4.” Chemical Portal - Chemistry Online Education, www.webqc.org/molecular-weight-of-C9H8O4.html. 3....