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Formation of Aspirin

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Experiment No. 2: Preparation and Recrystallization of Aspirin Name: Afifah Mustaffa Admission No: 1106361 Date of experiment: 8 November 2011 Date of Submission: 23 November 2011 1. Synopsis The objectives of this experiment were to familiarize students with the preparation of simple organic compounds and the process of recrystallisation to purify the compound. The experiment also allows students to conduct the synthesis of aspirin and also to enhance the students? skills of recrystallisation and determining the melting point of a substance. 1. Introduction 1. History of Aspirin In the past, it was discovered that salicin, which contained salicyl alcohol, was a main component of willow bark. Salicin was also found to be an organic compound. Salicyl alcohol and salicylic acid can be derived from the hydrolysis and oxidation of salicin. Even though salicylic acid proved to be a better pain reliever as compared to salicin, it caused irritation to the membrane lining in the stomach. The phenol-OH group forms acetylsalicylic acid when it is converted into an ester. Acetylsalicylic acid, also known as aspirin, seemed to have less harmful side effects and it was also more effective as a painkiller as compared to salicylic acid. Aspirin, a type of salicylate, is a white, crystalline solid. Although it is only slightly ionized in the stomach, which has an acidic pH, aspirin would ionize to give acetylsalicylate and hydrogen ions. ...read more.


Just enough hot solvent is added to dissolve an organic solid, which would form a saturated solution. When the solution cools, crystals would form in the funnel. However, there would be a slight deviation of the mass of crystals formed compared to the theoretical value of crystals formed. This is due to the solid dissolving in the cold solvent, which cannot be recovered. Having different solubilities is an important factor in separating the crystals from its? impurities. For impurities with very different solubility from its crystal, they can be separated by hot gravity filtration. As for impurities that are just as soluble as the crystal, recrystallization has to be carried out, or as an alternative, a different solvent may be used. 1. Procedure 4.1 Preparation of Aspirin Firstly, 2.4g of salicylic acid was approximately weighed out in a dry 100ml conical flask. The actual weight was recorded. 6ml of acetic anhydride was then added into the flask in the fume hood. The mixture was then swirled after adding 3 to 4 drops of concentrated sulfuric acid. To complete the reaction, it was heated in a water bath for 10 to 15 minutes. After removing the flask from the water bath, 1ml of distilled water is added carefully with a dropper while the mixture is still hot. ...read more.


1. Discussion From the experiment that was carried out, the temperature range of aspirin?s melting point was found to be between 133.4oC and 136.9oC. The theoretical melting point of aspirin is shown to be 134oC. The slight deviation in the temperature range may be due to the presence of impurities in the crystals. As the impurities cannot be completely eliminated from the final product, it may affect the results that were obtained in the experiment. As for the melting point, the presence of impurities would lower the melting point of a sample. Another experimental error which would have affected the results that were obtained was due to the use of sulfuric acid for the experiment. Sulfuric acid, a strong acid, would react strongly with organic molecules. This would affect the percentage yield of aspirin. A good substitution for sulfuric acid would be phosphoric acid as it is a weak acid; therefore it would react less strongly with the organic molecules and not affect the percentage yield at the end of the experiment. 1. Conclusion The experiment was unsuccessful as the percentage yield of aspirin that was obtained fell below the expected percentage yield. From calculations, the expected mass of aspirin that should be obtained was 3.123g. However, the mass obtained at the end of the experiment was only 1.23g, making the percentage yield of aspirin only 39.27%. This is probably due to the impurities that were still present in the solution, causing it to affect the yield obtained. 1. ...read more.

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