This experiment was aimed at synthesizing p-Acetamidobenzoic Acid. The synthesis was carried out by reacting a solution of potassium permanganate, p-methylacetanilide, and magnesium sulfate heptahydrate (MgSO4.7H2O). The weight of the dried product prepared was found to be 0.2670g and the melting point found to be in the range of 146C-149C. The p-Acetamidobenzoic Acid was not pure since its melting point was lower than the melting point of pure Acetamidobenzoic Acid.
The first step of the experiment involved the preparation of Potassium permanganate solution. In this case, 2.9g of KMnO4 was dissolved in 15mL boiling water and swirled to dissolve. While dissolving, additional boiling water was added to dissolve the undissolved potassium permanganate. The solution was then set aside for later use.
Next, 1.1 g of p-methylacetanilide, 2.9g of magnesium sulfate heptahydrate (MgSO4.7H2O), and 70mL of water were added to a 250-mL Erlenmeyer flask fitted with a stir bar. The mixture was then heated to 85C on a sand bath while stirring. Next, the hot solution of potassium permanganate was added to the solution of p-methylacetanilide via Pasteur pipet while stirring the solution of p-methylacetanilide vigorously. The hot solution of potassium permanganate was added slowly such that is took 30 minutes to add all the solution. After the addition, the resulting solution was stirred for 5 minutes. 4mL of ethanol was then added to react with the excess oxidant. Next, the solution was boiled until the color was dissipated. The brown manganese dioxide was then filtered off by pouring the hot solution through Celite on a fluted filter paper into a clean Erlenmeyer flask. The brown precipitate was then washed with hot water to dissolve the absorbed product.
Next, the filtrate was cooled in an ice bath and acidified with 20% sulfuric acid until a pH value of 3-4 was achieved. The product was then collected using vacuum filtration in which case the crystals were rinsed with small amounts of ice-cold water. The crystals were then dried thoroughly by continuing suction. 25 mg of the product was dried further and saved for characterization and spectral analysis.
The melting point of the dry p-Acetamidobenzoic acid was found to be in the range of 146C-149C. The weight of the product was also found to be 0.2670g. The prepared was not pure since it recorded a different melting point from the melting point of a pure
The melting point of the p-Acetamidobenzoic acid is expected to be in the range of 250C-252C. However, the melting point of the prepared product was found to be in the range of 146C-149C. This difference in melting point is attributed to the presence of impurities in the prepared product. Impurities reduce the melting points of substances. Even though efforts were made to remove as many impurities as possible, not all impurities could be removed. During the addition of potassium permanganate solution to the solution of p-methylacetanilide, the solution was added slowly to avoid the permanganate build-up. The IR Spectroscopy showed two strong C=O absorptions at 1700-1670 cm-1. On the other hand, in NMR Spectroscopy, the product showed one singlet for the CH3 protons at 2.3. One singlet for the aromatic protons around 7.3 was also recorded.
The experiment was successful since all the objectives were achieved. The product prepared was not pure since its melting point was found to be far much less than the normal range of a pure of p-Acetamidobenzoic Acid.