Synthesis of Aspirin Essay

1611 Words Jul 31st, 2011 7 Pages
In this experiment, acetylsalicylic acid was synthesized from the acidification of salicylic acid and acetic anhydride. The objective was to convert a specific amount of salicylic acid into the same amount of aspirin that was high in purity. Furthermore, the other objectives were to enable students to conduct the synthesis of aspirin, reinforce skills or recrystallisation and the technique of melting point determination. The amount of each compound should be the same because there is a 1:1 ratio between them. The purity of the synthesized aspirin was measured by determining its melting point and percent yield. Soluble impurities increase the range over which a compound melts and often decreases its overall melting point
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In precipitation, there is a rapid formation of a solid from a solution that usually produces an formless solid containing many trapped impurities within the solid's crystal framework. For this reason, experimental procedures that produce a solid product by precipitation always include a final recrystallization step to give the pure compound.

Figure: The esterification of salicylic acid by acetic anhydride5.

The -OH group of salicylic acid that reacts with acetic anhydride to form an ester-like product. The carboxylic acid group of salicylic acid remains unchanged. Acetic anhydride is used because it is cheap and forms a by-product, acetic acid. Acetic acid is non corrosive and can be recovered to produce more acetic anhydride.

2.4g of salicylic acid was weighed and poured into a 100ml conical flask. The actual weight was then recorded. In the fume hood, 6ml of acetic anhydride was added to the salicylic acid in the flask. To this mixture, 3 to 4 drops of sulphuric acid was added, swirled to mix and then heated in a water bath for 10-15 minutes to complete the reaction. The mixture was removed from the water bath while it was still hot and then 1ml of distilled water was added from a dropper carefully to decompose the excess acetic anhydride. An additional 40ml of cold water was added and stirred with a stirring rod to induce crystallisation. The crude product was collected by suction filtration and washed with a little cold

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