Preparation of Aspirin and Determination of the Melting Point

1445 Words6 Pages
Ferrer, Lara Melissa V.
Faculty of Engineering
University of Santo Tomas
Manila, Philippines

This experiment involved three steps: synthesis of aspirin, isolation and purification, and the estimation of purity of the final product. The synthesis involved the reaction of salicylic acid and acetic anhydride in the presence of a catalyst, phosphoric acid, H3PO4. When the aspirin was prepared, it was isolated and filtered. The percentage yield of the synthesis was calculated to be 78.42%. The experimental melting point range of aspirin was determined to be 122 -132°C. Due to its wide range, and lower value than that of the theoretical melting point of 136°C, it was
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Salicylic acid is also used in a variety of other personal care items such as dandruff shampoo, antiseptic and toothpaste. [2] METHODOLOGY
3.0g of salicylic acid was weighed then 3.0mL of acetic anhydride and 6 drops of 85% H3PO4 were added to it. The mixture was warmed over a water bath for 5 minutes while stirring. After warming, 20 drops of distilled water was slowly added. 15mL of water was added then the solution was heated until it became clear. It was allowed to cool and was placed in an ice bath until the solution becomes cloudy. Using pre-weighed filter paper, the mixture was filtered and was allowed to dry in the filter paper.
In determining the melting point range of the aspirin, a capillary tube (sealed at one end) was one-third-filled with the dried aspirin. The capillary tube and a thermometer were immersed in an oil bath. The temperature at which the solid started to melt and the temperature when the entire sample was completely liquefied were recorded as the melting point temperature range.


Aspirin was synthesized by reacting salicylic acid with acetic anhydride in the presence of phosphoric acid, H3PO4, as a catalyst:

The aspirin was synthesized when it was placed in a cold bath. Purification was necessary to remove any unreacted salicylic acid and acetic anhydride as well as the acetic product and phosphoric acid. Acetic acid and phosphoric acid are water soluble so they were removed by

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