Esterification is the reaction between carboxylic acids and alcohols to produce esters. Aspirin or acetylsalicylic acid was formed by reacting salicylic acid and acetic anhydride while Methylsalicylate was formed from salicylic acid and methanol, both in the presence of H2SO4 responsible for the removal of -OH to form an ester and donates H+ to protonate the salicylic acid. The reaction mixture in the synthesis of aspirin should be heated in temperature between 70-90°C for the formation of acetylsalicylic acid crystals that was further collected using vacuum filtration with cold water to wash out the impurities and further produced a 57% yield product. The synthesized methylsalicylate resulted to a minty odor that is used mainly as ointment or cream for treating muscle pains and sprains. Test using FeCl3 to verify the purity of the synthesized aspirin resulted to a violet-colored solution in acetylsalicylic acid making it an impure product because of the presence phenol group that must not be present in the structure. However, positive result in methylsalicylate turned the solution from clear to dark-green and further to a purple solution due to the presence of phenol group. The results of the experiment are therefore accurate and useful in knowing the importance and uses of organic products and knowing the process of esterification involving carboxylic acids and alcohols.
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Aspirin or acetylsalicylic acid from a family of chemicals known as salicylates is known to be an anti-inflammatory drug and used as a pain reliever (1). On the other hand, oil of wintergreen or methylsalicylate is an external analgesic used to treat muscle aches, sprain, and strains having anti-inflammatory and pain-relieving effects as well (4). Both the aspirin and methylsalicylate can be produced from salicylic acid, a natural occurring chemical in plants, consisting of two functional groups - carboxylic acid and phenol. The synthesis of acetylsalicylic acid and methylsalicylate from salicylic acid results in the formation of ester in the process called esterification where an acid reacts with an alcohol (2). The purity of the synthesized aspirin will be tested by using FeCl3 test where a purple color will determine the presence of the phenol group where the -OH group in the benzene ring will form a complex with Fe+3 (3).
MATERIALS AND METHODS
For the making of aspirin, a water bath with temperature ranging from 70-90°C was prepared while weighing 0.150 g of salicylic acid and dropped 85% H2SO4. Then, 0.3 ml of acetic anhydride was added to the reaction mixture and heated with the prepared water bath until it dissolved. Then, it was recrystallized in an ice bath after adding 0.2 ml deionized water. The formed aspirin was collected using vacuum filtration, washed with cold water, allowed to dry overnight and weighed again to calculate for the percentage yield. For the making of the Methylsalicylate, 0.25 g of salicylic acid was used and added 2.0 ml methanol until it dissolved. Then, 10 drops of H2SO4 was added and heated in the water bath for 15 minutes followed by allowing it to cool down in running water. The odor of the product formed was then determined. For the FeCl3, the synthesized aspirin and methylsalicylate were added 5 ml of distilled water and a drop of 1% FeCl3 to the test tubes for observations.
RESULTS AND DISCUSSIONS
Esterification involving salicylic acid and methanol will produce methylsalicylate that has pain-relieving and anti-inflammatory effects while salicylic acid and acetic anhydride in excess will form acetylsalicylic acid in the presence of H2SO4. The results and observations gathered in the experiment involving the FeCl3 test are summarized in Table 1.
Table 1. Data and Results for the Yield of Aspirin and FeCl3 Test
A. Yield of Aspirin
Mass of Salicylic Acid
Mass of acetyl salicylic acid
B. FeCl3 Test
Liquid; From clear to dark-green solution; Addition of cold water turned into dark purple
The aspirin or the acetyl salicylic acid was formed by reacting 0.150 g of salicylic acid with acetic anhydride with the presence of acid catalyst which is H2SO4 to speed up the reaction as well as being responsible in removing the -OH to form an ester. The acid catalyst donates H+ and protonates the salicylic acid as shown in Figure 1.
Figure 1. Reaction of salicylic acid with acetic anhydride
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Acetic anhydride was used for the reaction will be much faster and will produce a higher percentage yield (5). The reaction mixture was heated in the water bath with temperature between 70-90°C to aid in the formation of acetylsalicylic acid crystals and thus making the acetic acid as a byproduct. The salicylic acid dissolved while in the water bath due to the increased heat and increased solubility that made the solution colorless and allowed the salicylic acid white crystals to dissolve. The addition of water after removing the reaction mixture in the water bath aid in destroying the excess acetic anhydride that is unreactive. Then, recrystallization was performed in an ice bath since cooling of the mixture forms white crystals by decreasing its solubility. The aspirin was collected using vacuum filtration while washing it with cold water to separate the solid crystals as well as the removal of impurities in the crystals. After drying, 0.114 g of acetylsalicylic acid was obtained with a yield of 57% with calculations shown in Figure 2.
Thoretical yield = 0.150 g x x x = 0.20 g
Actual yield (Mass of acetyl salicylic acid) = 0.114 g
57%% Yield = x 100 = x 100 =
Figure 2. Calculations for the % Yield of the Synthesized Aspirin
The methylsalicylate or oil of wintergreen was also formed from salicylic acid where it reacted with methanol in the presence of H2SO4 again for the removal the -OH to form an ester in the reaction called esterification as shown in Figure 3. The sulfuric acid as a catalyst protonates the ester group while the methanol attacks the carbonyl group. As the carbonyl group was deprotonated, methylsalicylate formed.
Figure 3. Reaction of salicylic acid with Methanol
The product formed a minty odor that is used in food, perfumery, toothpaste, and candies or used as pain-reliever. The purity of the synthesized aspirin and methylsalicylate were tested using FeCl3 to test for the presence of phenol. The acetylsalicylic acid resulted to a violet-colored mixture indicating that the product formed has impurities since the synthesized aspirin or acetylsalicylic acid does not have an OH group, however, it turned violet or dark purple due to the presence of salicylic acid that didn't react purely in the process. On the other hand, methylsalicylate in FeCl3 gave a positive result where it turned dark-green and further into dark-purple due to the presence of phenol thus making the methylsalicylate as a pure product. Over all, the results of the experiment are accurate and useful in appreciating products that occur naturally as well as knowing how to synthesize aspirin and oil of wintergreen from salicylic acid.