Identifying a Constituent of Panacetin Essay
This experiment was a continuation of Experiment two, with a slightly different question to be answered. In this experiment, we are trying to find the identitiy of the unknown component of Panacetin. This is answering question 2 of the two questions that were to be answered in experiment 2. The equation of this reaction is as follows (and is the same as that found in
During this experiment, we used recrystallization methods in order to help in the purification of the unknown solid, as well as drying and vacuum filtration. We then ground the unknown and combined it with different chemicals (such as acetanilide or phenacetin) and used the melting point ranges to determine the identity. We used the Mel-Temp method in order to measure the melting points. (It is important to remember that if a chemical is mixed with a differing chemical, the melting point is decreased drastically, but if it is mixed with a component very similar in chemical make up, the melting point will not differ much from the expected.)
Observations and Data Throughout this experiment we saw recrystallization of the solid into a white crystalline structure suspended in liquid, and then vacuum filtered the unknown and put it into the Mel-Temp device in order to determine the correct melting point. We had pre-calculated that if it was acetanilide, there would need to be 31.6mL used to dissolve it, and if it was phenacetin, it would need 129.5mL to dissolve it. We ended up putting 129 mL of water in order to dissolve the crystals to begin the purification process. When we put the water into it, there was some of the unknown lost on the stirring rod, as well as solid impurities floating at the top of the mixture. Crystals began to form almost immediately, even before the mixture was put into the ice bath.
The crystals in this experiment were very much more white and crystalline/sparkly than those that we had in Experiment 2. By 3 minutes of being in the ice bath, the crystals were almost completely filling the flask, but were suspended in liquid. When we were pouring the mixture onto the filter paper, there was a slight spill and we lost some of the unknown, although it looked to be mostly liquid and not as many crystals. Also, when we washed the filtrate with cold water ice fell onto the filter, setting us back a few minutes, in order to wait for the ice to melt to not completely contaminate the weight. As it was filtered, there was a foamy texture to the liquid that was passing through, it was very bubbly until it reached the bottom of the flask, where it became liquid again. There were small crystals in the liquid.
When we measured the melting points, the melting point of compounds 1 and 2 was 127-137. We had the Mel-Temp apparatus start on 90 and end at 140. (All of the temperatures listed are in degrees Celsius.) For part 3 of the unknown, we began the apparatus at 90 and ended it at 120. We observed a melting point range of 80-90.4. For the fourth part of the compound, we began the apparatus at 100 and ended it at 140, and observed a melting point range of 111-133.8.
Results and Discussion
When we began, we had 1.49 g of purified unknown, which, when subtracted from the original number of 1.58g of solid we had before the purification process, leads us to determine that we had .09 g lost of impurities. The filter paper mass was .33g, the mass of the watch glass was 50.56 g, and the mass altogether was 52.38 grams. When calculated by adding both the watch glass, filter paper together and subtracting it from the total left us with 1.49 grams of purified unknown. We then subtracted that number from the original in order to get the amount of impurities lost. There were not a lot of calculations involved in this experiment.
The reason that we began the Mel-Temp apparatus at 90 and ended it at 120 for compound three was because it was the unknown added to acetanilide. Therefore, because the melting point of acetanilide is known to be 114, it seemed to be a good range. However, because the melting point range of this compound was observed to be 80-90.4, it can be determined that the unknown compound was added to acetanilide but was not acetanilide, because the lowering of the melting point of the known compound followed the idea that when two different compounds are mixed, the melting point for the known is decidedly lower than the original.
The fourth part of the compound, which was mixed with phenacetin, had a melting point range of 111-133.8, which was very close to the melting point of phenacetin, which is known to be 135. This is a strong indicator that the unknown that was added to the phenacetin is very chemically similar to the compound, because the melting point was not lowered. This is also again supported by the fact that the mixture of the unknown with itself (parts one and two) had a melting point range of 127-137.
This, paired with the fact that the amount of added boiling water in order to dissolve the original unknown compound (back in the purification stage) was 129 mL, further indicates that the unknown compound was phenacetin, because the pre-calculated amount of water that was needed to dissolve the phenacetin was 129.5 mL. Therefore we can predict, with some certainty, that the identification of the unknown compound in Panacetin is Phenacetin.
Experimental Recrystallization of the unknown drug compound was induced by boiling it with just enough water to dissolve it completely. It was then allowed to cool to room temperature. Recrystallization was induced by scratching the sides of the container with the stirring rod while it cooled, and then the unknown compound was placed in an ice bath. The solid was then collected by vacuum filtration, and was then washed with a small amount of ice cold water. The product was then dried to a constant mass and weighed in a tared vial. The unknown (now a solid) was ground into a fine dust using a watch glass with a spatula.
The solid was then divided into 4 nearly equal portions. Portions 1 and 2 were combined, and portion 3 was thoroughly mixed with an approximately equal amount of acetanilide. Portion 4 was then thoroughly mixed with an approximately equal portion of phenacetin. The melting point ranges of all four portions was then measured. For each of the portions, the temperature was recorded for the temperature at which the first trace of liquid was seen, and then again when the sample was completely liquid. The product was then turned in and labeled given the actual name of product indicated by the results.