Aspirin - Grade: A PDF

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Aspirin...

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Objectives The main objectives of this experiment are to produce aspirin by the acetylation of salicylic acid and also perform basic characterization such as melting point, solubility an TLC. Reference Table Name

Molecular

Molar Mass

Melting

Boiling

Density

Salicylic acid Acetic

Formula C7H6O3 C4H6O3

(g/mol) 138.12 102..09

Point (°C) 158.6 -73.1

Point (°C) 211 139.8

(g/cm3) 1.44 1.08

anhydride Phosphoric

H3PO4

97.99

42.35

158

1.88

acid

Materials 1. Iodine chamber 2. Filter paper 3. Test tube 4. Test tube rack 5. Hot water bath 6. Pipette bulb 7. Pasteur pipette 8. Spatula 9. TLC plates 10. Vacuum filtration apparatus 11. Beaker

12. Watch glass 13. Micro-capillaries 14. UV light 15. Scale 16. Mel-Temp apparatus 17. 85% phosphoric acid 18. Acetic anhydride 19. Salicylic acid 20. Melting point capillaries 21. Hirsch funnel Procedure Add 138mg of salicylic acid, one drop of 85% phosphoric acid and 0.3ml of acetic anhydride and mix thoroughly. Heat in a beaker at 90°C for 5-10 mins. Remove from heating source and add 0.5ml of DI water and stir for 1-2mins to cause decomposition of the excess acetic anhydride. Allow to cool to room temperature and put in ice for 5 mins, at this point a precipitate is formed. If a precipitate isn’t formed, put in the ice bath and scrap the insides of the test tube with a glass rod until a product is formed. Filter the precipitate using a Hirsh funnel. Place the solid product on a filter paper and press-dry and allow to air-dry for 5mins. Take the weight of your product, calculate its percent yield and melting point. TLC is conducted for the product vs commercial aspirin. Observe and take down your observations and comment on the purity of the product. In this part of the lab, add 65mg of product in 6.5ml of ethanol. Compare the product produced with the commercial aspirin tablet.

Results Characterization Data Experiment Melting Point (°C)

Aspirin (synthesized in the lab) 155

Solubility (Water vs Toluene)

Yes

TLC (Rf values)

5.3cm

Aspirin (commercial Comments sample) 138 The aspirin synthesized has a higher melting point than the commercial aspirin. Yes (partially) In the aspirin produced, it is completely soluble in water and toluene. In commercial aspirin, it is partially soluble in both water and toluene. 4.7cm The synthesized salicylic acid has the same Rf value with acetylsalicylic acid. The synthesized aspirin has a larger Rf value than the commercial aspirin.

Distance travelled by solvent = 5.9cm Distance travelled by acetylsalicylic acid = 5.3cm Weight of product = 0.093g Salicylic acid is the limiting reagent

Percent yield =

actual yield × 100 % theoretical yield

mass 0.138 g = =¿ molar mass 138.12 g 0.001mol mol

Moles of salicylic acid =

Moles of acetic anhydride,

mass=

(

)

density 1.08 g = × 0.3 ml=0.324 g ml volume

Moles of acetic anhydride =

0.324 g =0.0032mol 102.09 g mol

Theoretical yield=(0.001 mol)× 180.157 g /mol ¿=0.18 g

Percent yield=

0.093 g ×100 %=51.67 % 0.18 g

Conclusion In conclusion, aspirin was successfully synthesized with salicylic acid as the starting material and acetic anhydride as the reagent. A relatively poor yield of aspirin was formed. Errors in experimentation may have accounted for the low percent yield. The yield of the yield was probably low because hot water might have been used instead of cold water in the reaction. When the product is rinsed off with warm water, some of product is washed off as well. Based on the lab results, the purity of the product was proven by performing basic characterization tests. The melting point of the aspirin synthesized falls into the melting point range of salicylic acid. The distance on the TLC plate by the aspirin synthesized was exactly the same as the acetylsalicylic acid. This proves that the product formed was pure. When compared with commercial aspirin, it had a higher melting point. If the synthesized aspirin had any unreacted

salicylic acid in it, its melting point would have been lowered. The major constituent in commercial aspirin is salicylic acid which accounts for its lower melting point. Pre-Lab Questions 1. What type of reaction is formation of aspirin? An old bottle of aspirin can exhibit smell of vinegar, can you explain? Esterification reaction is involved in the formation of aspirin. Esterification is a substitution reaction where an -OH group in the salicylic acid reacts with the acetic anhydride to form an ester, aspirin. Aspirin is produced from the reaction of acetic anhydride and salicylic acid. The key compound in vinegar is acetic acid. With an old bottle of aspirin, the aspirin ages and undergo dissociation in the presence of moisture to give salicylic acid and acetic acid. 2. How does TLC help to evaluate the product purity in this reaction? Explain your answer by using hypothetical Rf values. TLC is a separation technique without requiring a lot of sample. It can be used to determine the purity of compounds. The reaction is completed because the TLC plate indicates when there is no more starting material left in the mixture. Post-Lab Questions 1. Explain the solubility and melting point differences for salicylic acid and acetyl salicylic acid. The melting point of aspirin is around 138-140°C and the melting point of salicylic acid is 158-161°C. When there are impurities in the crude product, the melting point would be lower compared to the melting point of the pure product. To purify pure aspirin even

more, it is important to note that both salicylic acid and aspirin are slightly soluble in water, but salicylic acid is more soluble than aspirin in ethanol. 2. Why is the free -OH group actively involved vs the -OH of COOH group during formation of aspirin? The phenolic -OH group is more nucleophilic than the acidic -OH group which is why acetylation occurs at the phenolic oxygen. In COOH group, the charge is distributed over the two oxygens. In the phenol, the charge remains on the oxygen....