After recrystallisation differences between the crude and purified aspirin were noted. The impure (crude) aspirin was powered and fluffy with small clumps and was slightly yellow in colour whereas the pure aspirin has a less fluffy crystalline powder and was whiter. This showed distinct differences in the two substances but similarities were also apparent showing aspirin, in some level, was created. Before recrystallisation the crude aspirin could of included impurities such as: Acetic acid (a product of the reaction process).
Recrystallisation helps to eliminate impurities; the precipitation process eradicates soluble impurities as aspirin has a higher precipitation temperature so converts to a solid while other impure components are left as soluble in the solution. The yield is calculated to look at how well the reaction has been completed. This reaction is simplified to: C7H6O3 + C4H6O3 > C9H8O4 + C2H4O2 To work out the yield; 0. 917g of 2-hydroxybenzoic acid (0. 917/138) * 180 138 (the molar mass of 2-hydroxybenzoic acid) 180 (the molar mass of aspirin) Theoretical yield: 1. 196g 3 d. p.
Percentage yield is worked out by Actual yield of synthesised aspirin: 0. 347g 0. 347/1. 196 * 100= 29 Percentage yield: 29% Melting Points CompoundBegan Melting (°C)Totally Melted (°C)Range (°C) Pure Aspirin1361-2 Crude Aspirin1251305 Product from Willow Bark1201255 The documented melting point for pure aspirin is 136°C. An impure compound will exhibit a lower melting point than this, which is what was observed in both the willow bark product and the crude aspirin. Pure aspirin has a narrow temperature range during which it changes from a solid to a liquid; this range is less than 2°C.
The sharpness of the melting point is useful to measure purity using pure aspirin as a comparison. As both types of aspirin melted over a temperature range of 5°C it’s indicative that both substances have many impurities. The range of melting points for the crude aspirin and product of willow bark in comparison to the pure aspirin is obvious and can show the level and amount of impurity in both compounds. Chromatography Different constituents of each mixture travel at different speeds along the paper causing the components to separate.
Above is a picture of the chromatography, comparing phenol (P), 2-hydroxybenzoic acid (2), pure aspirin (A), crude aspirin (I) and product from willow bark (W). Only two of the spots have been circled here, more were seen after this picture was taken but an image of the final separation was not photographed only observations were made (see table). CompoundRf value (numbered for multiple spots per compound) Phenol control4/6 = 0. 6 2-hydroxybenzoic acid4. 4/6 = 0. 73’ Pure aspirin5. 7-6 = 0. 95 Crude aspirin 0. 5/6 = 0. 083’ Product from willow bark1. 1. 2/6= 0. 20 2. 2. 6/6 = 0. 43’ 3. 1-6 = 0. 16’.
Rf = Retardation factor. The documented Rf for pure aspirin is 0. 56; however this experiment shows pure aspirin to be 0. 95, therefore for the purpose of comparison the documented value shall be used. This could be due to contamination, incorrect processes in the procedure, the amount of solution used or the temperature of the solution, although some of these factors are difficult to keep constant in the environment. The Phenol compound was used as a comparison. The result shows phenol is lighter than pure aspirin as it doesn’t contain as many atoms in its structure, with a molecular mass of 94.11 g/mol.
See Fig 1. 2-hydroxybenzoic acid, which is the main metabolite of aspirin, shows it is also molecularly lighter (in that it is moved further up the paper when soluble) than crude aspirin or pure aspirin. We would expect to see this because crude aspirin consists of the mass of 2-hydroxybenzoic acid and other compounds giving a total mass of 138. 12 (g mol-1). The pure aspirin shows only one spot on the paper, this is because it consists of only one compound, that being 2-acetoxybenzoic acid (aspirin). Pure aspirin has a molecular mass of 180.
157 (g/mol). The synthesised crude aspirin also shows only one spot but this is very far away from the pure aspirin Rf, although it could consist of multiple components close in mass so they merge into one spot. This clearly qualitatively shows the level of impurity as it is much heavier showing it contains other compounds weighing it down, which it should not have if synthesised meticulously. The willow bark product produced 3 spots on the paper which indicates it has multiple constituents all heavier than pure aspirin therefore is impure.
This was expected because of the source, although the TLC (thin layer chromatography) paper could have been accidently splashed with an organic compound during the experimentation process and thus distorting the results by showing extra spots, this is unlikely as it’s expected that the willow bark product will be heavily impure. The paper also shows an elongated spot which is due to the solution being too concentrated. Fig 1. Aspirin StructurePhenol Structure 2- Hydroxybenzoic Willow Bark Synthesis Acid structure Chemical tests 1.
Reaction with sodium carbonate CompoundObservations Phenol—— 2-hydoxybenzoic acidBubbled, clumped and floated to the surface of solution Crude aspirin—— Pure aspirin——- Product from willow bark—— Phenol served as a comparison for the sodium carbonate to show it didn’t produce a reaction when it shouldn’t have. An above observation was made when sodium carbonate reacted with 2-hydroxybenzoic acid which was expected due to CO2 being released when an acid and a carbonate combine, below shows the reaction that took place.
C7H6O3 + Na2CO3 > NaC7H5O3 + H2O + CO2 No reactions were observed for the crude or pure aspirin which revealed the 2-hydroxybenzoic acid had formed a new product during synthesis which has no reaction with sodium carbonate. This was the outcome required and was achieved based on this test. The product derived from willow bark also showed no reaction as it had no component within it that reacted with sodium carbonate, no acid group within this natural product. 2. Reaction with Fe3+ CompoundColour with Fe3+.
PhenolIntensely Purple 2-hydroxybenzoic acidPurple and frothy Crude AspirinPale purple, almost translucent Pure AspirinLight brown Product from Willow BarkBlack A solution presenting purple when mixed with an iron group shows the presence of a Phenol group. All mixtures, apart from the pure aspirin, exhibited this although all varied in colour intensity. Aspirin doesn’t have a Phenol group as can be seen from the lack of purple in the solution so this can be used as a control along with the phenol solution itself.
From this test it can be seen, to what degree each compound has a phenol impurity. The solution containing the crude aspirin only changed to a slight translucent purple indicating a low level of 2-hydroxybenzoic acid (as can be seen this compound reacts strongly to the addition of Fe) and so the crude aspirin has impurities but only to a certain degree. The pure aspirin shows how a compound with less impurities shouldn’t contain phenol and how this reacts in the solution and what colour should appear, colours away from this contain impurities.
The willow bark product displayed an intense black colour, possibly so purple it looked black, so far away from the pure aspirin colour that contaminations are certain. Evaluation All procedures and processes of each stage of synthesis had variables that could result in an impure product. Although the recrystallisation stage, to remove impurities, was performed by an experienced laboratory staff member errors could still have occurred and these must be considered.
Before the crude aspirin was recrystallised it may have contained various impurities that were not all eradicated by the precipitation process, these could include: contaminations in the air and C2H4O2 (a product of the original reaction), along with contaminations in the distilled water used, although this is better than using tap water. A high or even moderate yield was not achieved. This could be due to many factors; the experience of the chemists producing the aspirin having a poor laboratory technique, thus procedures were not carried out effectively and without error.
Percentages of the substances could have been lost or misplaced during stages of the procedure. Other variables that could lead to the yield being less than 100% are: transfer of the product between containers, an incomplete reaction could have occurred, and is likely to have, where each compound does not fully react when it should due to factors beyond control, this will lower the products final mass. Recrystallisation also loses product and therefore yield as some product may still be left in the solution or on the filter paper. The aspirin may not have dried properly; making the mass higher therefore the purity would be lower.
This factor could have distorted all results consequently when comparing, all would have the same distortion. The melting points may have inaccuracies as the temperature at which the willow bark melted was debated by the group. Lack of concentration and difficulty in determining when it had melted may have led to the product melting fully before it was observed and this would lead to a distortion of the results. It would be expected that the willow bark would melt at a higher temperature that the crude aspirin as it is known to have more impurities. Conclusion
The overall objectives were to synthesise aspirin from 2-hydroxybenzoic acid and willow bark, and qualitatively determine the purity of each product, this was achieved as aspirin was produced from both the willow bark and the substances. The results from all tests do display that there were impurities, although they did not all show a consistent level of impurity. There was a noted difference, but not greatly so, in appearance between the crude and pure aspirin when tested with the Fe3+ solution. In contrast the TLC test exhibited a drastic comparable difference between the crude and pure aspirin.
Possibly this was because the TLC did not use a subjective scale like the other tests, the quantitative measurability of the results allowed the outcome to be easily compared to the other products and against the pure aspirin. All tests showed a qualitative visual level of impurity in the results. Although this level varied and cannot be compared due to the difference in format of the results for each test, it can be seen, in general, that the crude aspirin contained more impurities than the pure aspirin and the willow bark product was the most impure of them all.
This was expected. Although a ‘pure’ aspirin was synthesised from the crude, this is still an aspirin substance synthesised in a college laboratory by college students who are not skilled in laboratory practice and could have contaminated the experiment at various stages and not been astute enough to record and monitor reactions well. This could lead to the ‘pure’ aspirin only being a certain level of pure itself therefore any comparisons made against it are relative to that aspirin not the aspirin on the market/in stores.
This can be seen in the chromatography test where documented aspirin has a retardation factor of 0. 56 but the synthesised pure aspirin is much lighter meaning it may not contain all the compounds found in correctly synthesised aspirin. To conclude if all variables and experimenter error was controlled a purer product would have been made and a higher yield would have been produced. Not all variables can be accounted for and therefore a 100% yield can never be achieved, even in a manufacturer setting.
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