How is salicylic acid is converted into aspirin give equation?
Answers
Aspirin is the common name for the compound acetylsalicylic acid, widely used as a fever reducer and as
a pain killer. Salicylic acid, whose name comes from Salix, the willow family of plants, was derived from
willow bark extracts. In folk medicine, willow bark teas were used as headache remedies and other
tonics. Nowadays, salicylic acid is administered in the form of aspirin which is less irritating to the
stomach than salicylic acid. To prepare aspirin, salicylic acid is reacted with an excess of acetic
anhydride. A small amount of a strong acid is used as a catalyst which speeds up the reaction. In this
experiment, phosphoric acid will be used as the catalyst. The excess acetic acid will be quenched with
the addition of water. The aspirin product is not very soluble in water so the aspirin product will
precipitate when water is added. The synthesis reaction of aspirin is shown below:
Since acetic acid is very soluble in water, it is easily separated from the aspirin product. The aspirin
isolated in this step is the “crude product”. A “purified product” can be obtained through
recrystallization of the crude product in hot ethanol. In this experiment, the crude product will be the
desired product. The percent yield of the crude product will be determined for this reaction. The purity
of the product will also be analyzed. The product will be analyzed by three different methods: melting
point, titration, and spectroscopic assay.
The melting point range of pure aspirin is 138-140 C and the melting point range of the salicylic acid
starting material is 158-161 C. If impurities are present in your crude sample, the melting point range
for your product will be lower than the range of pure aspirin. Also, your melting point range may be
greater than 2 degrees.
From the titration of your sample, the moles of acetylsalicylic acid present can be determined assuming
that there is not a large percentage of an acid impurity present in your crude sample.