Restatement of experiment: Aspirin (acetylsalicylic acid) is a derivative of salicylic acid with the same medicinal values but fewer side effects. It is used widely as a pain killer and anti-inflammatory. In this experiment, aspirin was synthesized from salicylic acid and acetic anhydride. To determine the product’s purity, the melting point of aspirin was then measured using a Thomas-Hoover Uni- Melt device. The product had a low percent yield and was found to be impure due to its low melting point. Result: Percentage yield (%).
Compound Theoretical yieldActual yield Percent yield Acetylsalicylic acid0. 16g0. 21g76. 29% Table 1. The theoretical yield of acetylsalicylic acid based on the amount of salicylic acid used for the reaction. Compound Observed M. PReal M. P Acetylsalicylic acidImpure: 135 – 136 Pure : 133 – 136138 Table 2. The observed melting point of acetylsalicylic acid compared to its literature melting point. Calculation of mass of crude product before recrystallization of aspirin: Mass of 125mL Erlenmeyer flask = 25. 32g Mass of flask w/ crude product = 25.
48g (Mass of flask w/ crude product) – (Mass of flask) = Mass of crude product 25. 48g – 25. 32g = 0. 16g crude product Discussion Table 1 shows how much acetylsalicylic acid was synthesized compared to how much salicylic acid was used. Since there is a 1:1 ratio between the two, then the amount of salicylic acid used should be equal to the amount of acetylsalicylic acid recovered at the end of the experiment. As Table 1 shows, this is not the case, for 0. 21g of acetylsalicylic acid was harvested when 0. 16g of salicylic acid was used.
This could have some effect on the purity; for the melting point of the harvested acetylsalicylic acid was not close to the literature melting point (see Table 2). Since the final product was determined not to be very pure, it is highly likely that less than 0. 21g of the product was acetylsalicylic acid. Further analysis of the product will have to be done to determine exactly how pure the product actually was. There were several problems that could have contributed to the low purity or mediocre percent yield.
When dissolving the initial amount of salicylic acid in the solution of acetic anhydride and concentrated sulfuric acid, it did not completely dissolve into the solution, even when it was heated. This could have a slight impact on the results of the overall yield of aspirin because it was possible that not all of the salicylic acid was synthesized. To determine if this affected the synthesis of aspirin at all, the experiment should have been ran a second time to see if the same thing occurred.
The iron (III) chloride test also could have been ran to determine if any of the aspirin degraded to salicylic acid or never converted from salicylic acid. IR Test: The result of IR test is attached back of the report. IR spectrum of your recrystallized product, where it will be compared to a known spectrum available below. Under the supervision of our instructor, you will take a small sample of your dry purified aspirin and analyze via a Fourier Transform Infrared (FTIR) spectrophotometer. Functional group recognition amongst the various absorption peaks should be noted.
A molecular compound can be identified by the IR radiation it transmits or absorbs. At specific frequencies, the atoms of the molecule stretch, twist, and bend around the bonds joining them. Radiation of the wavelengths corresponding to those frequencies will be absorbed. The energy absorbed must agree in frequency with the natural frequency of vibration of the molecule. In using the IR spectrophotometer, a sample of the compound is subjected to varied wavelengths of IR radiation. Certain wavelengths will be readily absorbed by the molecule depending of the structure of the molecule.
The various wavelengths absorbed by the compound are measured and recorded graphically. A unique continuous absorption spectrum, an IR spectrum, can be plotted for each molecular compound. Comparison with known spectra will reveal the identity of the compound just as fingerprints reveal the identity of a person. An IR spectrum is a plot of wave number (X-axis) vs. percent transmittance (Y-axis). Percent transmittance tells us how much IR energy was transmitted through the sample. It can also tell us how much energy was absorbed by the sample.
For example, a high degree of transmittance indicates that little IR energy was absorbed and most of the IR energy passed through the sample. The wave number scale on the spectrum indicates the energy of the IR incident on the sample. The IR spectrum of hexanoic acid is shown below (Figure III). Take a minute to look over this spectrum. The deep downward peaks are areas of low IR transmittance and high IR absorbance. Notice that there are areas that are flat areas where very little IR energy was absorbed (nearly 100% transmittance).