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In the late 1700s, it was discovered that the bark of the willow tree could effectively treat pain and fever. The active compound in the bark, salicin, was isolated in 1829, and in 1838, salicylic acid was first produced from salicin. In 1897, a pure and stable form of acetylsalicylic acid, known as aspirin, was synthesized (1). When cells are damaged, they release arachidonic acid (2). Cyclooxygenase (COX) enzymes convert arachidonic acid into prostaglandins and thromboxane, which have pro-inflammatory roles, leading to increased temperature, swelling, and pain (3).
Aspirin works by irreversibly inhibiting COX enzymes. It binds to the activation site of cyclooxygenase, preventing the conversion of arachidonic acid into prostaglandins and thromboxane, resulting in a reduction of body temperature, pain, and inflammation.
The aim of this experiment was to hydrolyze aspirin using sodium hydroxide (NaOH) and sulfuric acid (H2SO4) to obtain a sample of salicylic acid (2-hydroxybenzoic acid).
| Name of Chemical | Molecular Weight (g mol-1) | Melting Point (°C) | Boiling Point (°C) | Density (g cm-3) | H-phrases/PH/P phrases |
|---|---|---|---|---|---|
| Aspirin | 180.16 | 135 | 140 | 1.39 | H302, P301, P312, P330 |
| NaOH (10% w/v) | 39.99 | -10 | 105-140 | 1.08 | H290, H314, P280, P301 + P330 + P331, P305 + P351 + P338, P310, P234 |
| Salicylic acid | 138.12 | 159 | 211 | 1.439 | H302, H318, H361d, P201, P202, P280, P301 + P312, P305 + P351 + P338 |
1.0167g of aspirin was added to a test tube along with 10ml of 10% w/v sodium hydroxide.
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The solution was swirled until the aspirin dissolved. The test tube was placed in a steam bath for 5 minutes and was then cooled in ice for approximately 6 minutes.
In a fume cupboard, concentrated sulfuric acid was added dropwise to the test tube. Sulfuric acid was added until the pH fell below 2. When the pH reached 2, a white precipitate formed in the test tube. A Buchner funnel under vacuum was used to filter the precipitate from the test tube. Deionized water was used to wash the precipitate. The mass of the product was weighed again and recorded as 0.2044g. This product was left to dry in the oven at 80℃ for approximately 30 minutes. When the product came out of the oven, the mass was recorded as 0.1921g.
Percentage yield
Aspirin is the limiting reagent as NaOH is in excess
% Yield = (mass of product obtained / theoretical mass of product) x 100
Theoretical mass of product:
Aspirin
Mass / Mr = moles
1.0167g / 180 = 0.005648 moles of aspirin
Moles aspirin x Mr of salicylic acid = theoretical mass of salicylic acid
0.005648 x 138 = 0.77947 g
(0.1921 / 0.77947) x 100 = 24.65% yield
| Absorbance (cm-1) | Assignment (stretching frequencies) | Typical Values (cm-1) | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Aspirin | 2997 | 2969 | 2870 | 2833 | 2697 | 2587 | 2549 | 1752 | 1682 | OH (R-C-O-O-H) | C=O (R-C-O-O-H) | OH 3300-2500 | C=O 1655-1740 |
| Salicylic acid | 3233 | 3006 | 2855 | 2594 | 1655 | OH (R-C-O-O-H) | C=O (R-C-O-O-H) | OH 3300-2500 | C=O 1655-1740 |
Melting point of experimental salicylic acid: 154-156°C
Literature melting point of salicylic acid: 159°C (14)
The IR data showed correlation between the two samples due to the presence of the carboxylic acid functional group. The values for the C=O and OH bonds in aspirin (C=O 1655-1611cm-1, OH 2997-2549cm-1) and salicylic acid (C=O 1682-1607cm-1, OH 3233-3006cm-1) were similar. The key difference was due to the ester functional group on aspirin, where the IR spectrum showed a peak at 1752cm-1, which was not present in the spectra for the salicylic acid sample. This clearly indicated that the product generated was distinctly different from the reactant. The absorbance values for salicylic acid functional groups (C=O 1655 cm-1, OH 2855-3233cm-1) fit within the literature data (C=O 1655-1740cm-1, OH 3300-2500cm-1). This correlation indicated that the key functional groups were present. The melting point indicated that salicylic acid was synthesized as it is close (within 5°C) to the literature value. The melting point may have been lower due to impurities in the product that disrupted the structure and increased the variation of intermolecular forces, therefore lowering the melting point.
A white powder was generated in 24.65% yield from the base-catalyzed hydrolysis of aspirin. The melting point of the experimental sample (154-156°C) was distinctly different from the starting material of aspirin (135°C) (15) and correlated with published values (159°C) (14). In addition, the IR spectra for the experimental product was different from the reactant, with the key C=O ester stretch at 1752cm-1 in the aspirin spectra absent in the salicylic acid spectra. The generated IR data from the sample also matches literature values for the key functional groups on salicylic acid. Due to the similarity of literature values in the melting points and IR spectra of the experimental product as well as the difference in IR data between aspirin and salicylic acid, it can be concluded that the experimental sample generated from aspirin was salicylic acid.
If a patient experiences one or more cardiovascular events, they are at very high risk for another event (16) and so secondary prevention aims to prevent cardiovascular events such as myocardial infarction (MI) or ischemic stroke from occurring again. The synthesis of the cyclooxygenase (COX) enzyme produces Thromboxane A2. Thromboxane A2 promotes platelets to adhere to vessel walls (adhesion), clump together (aggregation), and causes blood vessels to narrow (vasoconstriction) (17). This platelet effect can cause a blockage of blood to the heart, which can result in MI or to the brain, which can result in ischemic stroke (18). Aspirin irreversibly inhibits COX in platelets, preventing the synthesis of thromboxane A2 (19). The platelet lifespan is seven days, which means that after aspirin is taken, both the COX enzyme and Thromboxane A2 cannot be synthesized until new platelets are brought into circulation. As a result of the platelet lifespan, the antiplatelet effect can be brought about with low doses of aspirin (17).
The 1 H NMR can indicate whether the reaction was successful. Aspirin has an ester group which salicylic should not have. The 1HNMR for aspirin shows a shift at 1.67 (this represents the CH3) and a shift at 3.45 (represents the CH2) which should not be present on the spectra for salicylic acid if the reaction is successful. Furthermore, the spectra for salicylic should feature a shift at 15.2 due to the OH group which is not present in aspirin due to the ester.
Aspirin tablets may have an enteric coating on the surface to avoid dissolution in highly acidic pH conditions (the stomach) and therefore control the release of a drug. The enteric coat stays intact in the stomach but breaks down when the medication reaches the small intestines (where conditions are more basic) (20). Aspirin has been found to irritate the gastrointestinal (GI) mucosa through back-diffusion of acid. As a result, the mucosal cells and capillaries can become injured, tissues and cells can die, and bleeding can occur. However, enteric coating can be used to prevent these gastrointestinal issues because enteric-coated aspirin causes less damage to the GI mucosa than plain or buffered versions of the drug (21).
Hydrolysis of Aspirin: Lab Report. (2024, Jan 06). Retrieved from https://studymoose.com/document/hydrolysis-of-aspirin-lab-report
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