Chem formal lab report final

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Multistep Synthesis of Acetylsalicylic Acid with TLC and IR Analysis Saba Shakil Armaghan Khosravi Section 14 CHY-142 1

Introduction The fascinating phenomena of the human brains insensitivity to pain has long captivated scientists and researchers studying medicine. The brain interprets pain signals because it lacks pain-sensitive receptors, in contrast to many other regions of the body (N/A, 2023). This fascinating facet of neurophysiology emphasises how important pain has been to our evolutionary process. Pian acts as a natural alarm system, warning people about possible danger and directing them to take precautionary action (Bluemrath, 2023). The discovery of synthetic pain treatment dates to 1897, when German chemist Felix Hoffman accomplished a historic first by creating the first acetylsalicylic acid (ASA). This novel approach contrasted with conventional treatments such as white willow, which had become less popular because of their corrosive qualities. During the first part of the experiment, an aqueous base and methyl salicylate react chemically. Several products are produced by this reaction, including water, methanol, and most notably, the sodium salt of salicylic acid. Sulfuric acid is added to this combination to refine it, which causes the sodium salt to change into a free acid. As a result, methanol and salicylic acid are the main organic products of this reaction. A crystallization procedure can be used to separate and purify salicylic acid in its solid state. Interestingly, until the late nineteenth century, the principal way to produce salicylic acid was by saponification of methyl salicylate (Bluemrath, 2023). This approach persisted until it became possible to synthesise salicylic acid from coal tar at a reasonable price. The balanced chemical equation that shows this reaction can be written as 2

The creation of acetylsalicylic acid (ASA) is the focus of the experiments second phase. The phenolic hydroxyl (OH) group of salicylic acid and the acetylating agent, acetic anhydride, are catalysed by acid in this synthesis, which results is the ester acetylsalicylic acid. As a nucleophile in this reaction, the phenol group starts a substitution process at one of the acetic anhydride’s carbonyl groups. Notably, acetic anhydride has two functions in the reaction, it is a reactant and a solvent. Due to its high level of reactivity, this substance can acetylate other nucleophilic groups and, in the presence of a catalyst, react with phenols and alcohols. What makes this reaction unique is that it doesn’t require as much heating, a mild warming of the reaction in a warm bath would do just fine. As a catalyst, sulfuric acid is used to enable effective synthesis. Water is used to neutralise the excess acetic anhydride when the reaction is finished. The balanced chemical equation for the synthesis of aspiring can be written as: 3

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The third week of the lab experiment is dedicated to the products purification and analysis, which calls for a wide range of methods. The first test used to determine the purity of a substance is the melting point test, a traditional technique based on comparing the range of measured melting point with a value found in the literature. A small sample of the solid substance is heated gradually during this process, with the temperature rising at a regulated rate of 1 ℃ / minute. For comparison analysis, the ferric chloride test will be carried out concurrently on starting materials, intermediates, products, and related chemicals. FeCl 3 reacts with solutions containing phenols, enols, certain carboxylic acids in either compound to produce characteristic changes in this test that help identify and assess the substances being tested. Thin-layer chromatography (TLC), which is intended to efficiently separate and identify compound mixtures, is another crucial technology in this procedure. The foundation of TLC is the interaction of two phases: The mobile phase which transports the substance along the stationary phase, and the stationary phase, which partially absorbs the compounds. The prepared acetylsalicylic acid, together with additional reactants and intermediates, will be the focus of the TLC expedition. Methyl salicylate, salicylic acid, and acetylsalicylic acid samples are spotted onto one end of a plate after being dissolved in the proper solvent (Belle, 2011). The plate is placed into a developing tank with a tiny amount of a developing solvent once it had dried. The solvent moves up the plate through capillary action, which makes it easier for the components to travel in different directions along the plate. Finally, but just as importantly, infrared spectroscopy (IR), a method for determining energy absorbance, comes into focus. Understanding the motions and vibrations that take place between atoms within a molecule is possible because of the absorption frequency. Through 4

spectral analysis, the combination of these absorbances creates a distinctive fingerprint that facilitates compound identification. To determine the different compositions and purities of crude and pure acetylsalicylic acid, their infrared spectra will be compared. These many methods highlight how thorough our investigation is and guarantee a thorough assessment of the synthesised chemicals. Experimental: Week 1: Part A - Saponification of Methyl Salicylate In the first step of the process, 5.0 grammes of methyl salicylate were precisely weighed and added to a 250 mL round-bottom flask that had been previously weighed. Next, 50 millilitres of a 20% NaOH solution were added to the identical flask. It's significant to note that, although it might have formed at this point, the white solid quickly dissipated when heated. A couple of boiling chips were added to the flask to prevent bumping during the heating process, and a reflux condenser was fastened to it using lightly lubricated ground glass joints to aid in the reaction. After that, the solution was carefully boiled for about 20 minutes, making sure the reflux level in the condenser stayed in the middle. The mixture was heated and then allowed to cool to room temperature. After cooling, the mixture was moved to a 600 mL beaker, and 250 mL of 1M sulfuric acid was slowly added to make the mixture acidic (as indicated by the pink colour of litmus paper). To precipitate the salicylic acid, an extra 25 mL of sulfuric acid was added if the litmus paper did not show any acidity. The mixture was allowed to cool down in an ice bath for a further five to ten minutes. The mixture's level of chill was checked using a hand test. Before adding the bulk of crystals, most of the liquid supernatant was decanted using a Buchner funnel to aid in filtration. After letting the cool mixture settle, the product was extracted using a 5

Buchner funnel and vacuum filtering. After weighing the crude salicylic acid, a small number of crystals was reserved for chemical testing, melting point analysis, and Thin-Layer Chromatography (TLC) examination. Part B - Purification of Salicylic acid In a 250-millilitre beaker, the crude salicylic acid was recrystallized. First, the solution was brought to a boil so that the crystals could dissolve entirely. The beaker was then taken off of the heat source, set down on a bench, and covered with a watch glass. As the solution cooled to room temperature, it was crucial to make sure there was no movement, jiggling, or other disruptions. If crystal formation was absent, the inside surface of the beaker was gently scratched below the liquid level in order to promote crystal growth. This scratching produced tiny glass crystals that acted as seed crystals to encourage more recrystallization. The beaker was placed in an ice water bath to aid in recrystallization as soon as the filtrate reached a comparatively cool temperature and crystals of salicylic acid started to form. Salicylic acid crystals were recovered by vacuum filtration once the liquid had cooled to an ice-cold state for at least ten minutes. The crystals were then washed with tiny amounts of ice-cold distilled water from a wash bottle that had been refrigerated beforehand. After the liquid was removed with a vacuum, the crystals were carefully stirred with a stirring rod so as not to scratch the filter paper. The crystals were moved to a 50 mL beaker that had been cleaned, dried, labelled, and reweighed in order to store them until the next week. Week 2: Part A - Saponification of Methyl Salicylate 6

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During the second week of the experiment, melting points were measured for both the purified salicylic acid and a fraction that was kept for Thin-Layer Chromatography (TLC) examination. The salicylic acid from the previous session was weighed. Part B - Synthesis of Aspirin About 100 millilitres of distilled water were heated to 45 to 50 degrees Celsius in a 400- millilitre beaker with four boiling chips within to create a warm water bath. Next, a top-loading balance was used to weigh 3.0 grammes of salicylic acid into a 100 mL beaker that had been well cleaned and dried. Next, the salicylic acid in the beaker was mixed with 5.0 mL of acetic anhydride, which was measured in a 10 mL graduated cylinder. Five drops of strong sulfuric acid were carefully added to the beaker, and a glass rod was used to vigorously agitate the liquid. The mixture was gradually heated in the warm water bath for five to fifteen minutes while being constantly stirred to ensure the solid was fully dissolved. With further melting and heating, the first created oil-like substance should disappear. Acetylsalicylic acid crystals began to form when the reaction vessel was taken out of the water bath and left to cool naturally to room temperature. The vessel was then set on ice to allow the fluid to thicken into a semi-solid form. A glass rod was used to lightly scratch the inside of the beaker to encourage crystal formation if crystallisation did not occur after cooling. 50 mL of ice-cold distilled water was added when the crystallisation process was finished. The unrefined aspirin crystals were separated using vacuum filtering and then repeatedly cleaned with little amounts of cooled distilled water. To guarantee a complete washing without causing damage to the filter paper, the crystals were gently stirred with a glass stirring rod for five minutes while the suction was maintained. Using a top-loading 7

balance, the crystals were then cautiously moved from the filter paper to a dry, clean, and pre- weighed plate. Part C - Recrystallization After adding the raw aspirin crystals to a 250 mL beaker, 20 mL of hot water was added to the beaker to dissolve the crystals once again. There was no need to add more water because the crystals could be completely dissolved with 20mL of it. After that, a watch glass was placed over the beaker, and it was let to cool to room temperature. The beaker was then placed in a cold bath to facilitate crystallisation. Following the completion of crystallisation, the refined crystals were cleaned in ice-cold water, and vacuum filtering was used to extract the pure aspirin. After achieving maximum drying, the crystals were placed in a 50 mL beaker that had been cleaned, dried, and tagged. The Teaching Assistant was then given the beaker to store the crystals until the next lab session. Week 3 Part A – Weight the acetylsalicylic acid Salicylic acid generated in the preceding lab experiment was collected and weighed. After that, a small sample of the chemical was subjected to a melting point examination. Part B – Thin Layer Chromatography (TLC) Before starting the thin layer chromatography, the necessary chemicals and supplies were acquired. Furthermore, samples of the crude and refined aspirin, as well as the purified salicylic acid, were dissolved in a 50:50 dichloromethane: ethanol mixture. A line was drawn with a pencil, approximately 2 centimetres from one end of the plate. The line was drawn thinly so as 8

not to puncture the plate. The standards compounds and the aspirin and salicylic acid generated samples would be visible at this point. The sequence in which the spots will be applied was plotted on a map and noted in the lab notebook. For every chemical, a total of six lanes were created. These included the manufactured samples of crude and refined aspirin, as well as the reference samples of methyl salicylate, salicylic acid, and aspirin. Up to 4 microliters of solution were drawn using each capillary tube at each standard station. To prevent contamination, it was crucial that these tubes not be moved from one station to another. After filling the capillary tubes with each solution, the plate's surface was softly dabbed with each capillary tube in the corresponding marked lanes, letting the solutions seep into the silica gel. The plate was left to dry for two to three minutes after each lane was spotted with the appropriate solution. After that, the plate was carefully inserted into the developing chamber so that the spotted samples on the bottom of the plate touched the chamber's solvent. The solvent was permitted to climb the plate at its own speed. The plate was gently taken out of the chamber once the solvent had travelled up to around 80% of its journey. The solvent front was immediately drawn onto the plate prior to evaporation. The plate was then put in a fume hood and left to dry for ten minutes. All the marks that were visible to the unaided eye were traced after they had dried. Once these spots had been traced, the plate was placed in a dark fume hood and exposed to UV light. This allowed the spots that were visible because of the UV light to be traced. The measurement was made in the laboratory notebook from the start line to each spot's leading edge. Which were made visible by UV light and traced. Every spot's leading edge was measured from the start line, and the measurement was entered into the lab notebook. 9

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Part C – Chemical Test Three tubes in all, labelled #1 through #3, were collected for the ferric chloride test. Samples of the generated compounds—purified salicylic acid and both crude and purified aspirin —were placed in each tube. Following the placement of the samples in the tubes, 0.5 mL of ferric chloride was added, and the tube was gently swirled to aid in mixing. The physical alterations that were noticed were noted in the lab notebook. After the test, the test tubes were cleaned, and the solutions were disposed away for further usage. Part D: Infrared Spectroscopy To perform infrared spectroscopy, aspirin and salicylic acid that had been purified were separated into tiny quantities. Using computer software, the spectra of each component were acquired by centering each sample in the spectrometer. Results and calculations Table 1: Literature values of all reactants Compound Name Formula Molecular Weight (g/mol) Melting point ( ℃) Density (g/mL) Methyl Salicylate C 8 H 8 O 3 152.148 -8.50 1.174 9 Sodium Hydroxide NaOH 39.997 323.0 1.515 10 Water H 2 O 18.015 0.00 1.0 Acetic Anhydride C 4 H 6 O 3 102.089 -73.40 0.916 11 Sulfuric Acid H 2 SO 4 98.079 10.31 1.83 Methanol CH 3 OH 32.042 -97.50 0.7866 Table 2: Literature values of all products Compound Name Formula Molecular Weight (g/mol) Melting point ( ℃) Density (g/mL) 13 Salicylic Acid C 7 H 6 O 3 138.121 158.60 0.1443 Sodium Bisulfate NaHSO 4 120.061 58.50 2.435 10

Methanol CH 3 OH 32.042 -97.50 0.791 Acetylsalicylic Acid C 9 H 8 O 4 180.158 136.0 1.35 Acetic Acid C 2 H 2 O 2 60.052 17.0 1.048 The most important reactants and products utilised in the experiment are listed in Table 2 together with their calculated percentage yields, recorded masses, and melting point ranges. The Formula used to calculate Percentage yield = Actual yield Predicted yield x 100 The fact that 1 mol of salicylic acid reacts with 1 mol of acetylsalicylic acid should be noted. This mole ratio can be used to compute the theoretical yield. The following method can be used to compute the theoretical yield given that the mass of salicylic acid utilised is 3.0 g, its molecular weight is 138.12 g/mol, and its molecular weight of acetylsalicylic acid is 180.16 g/mol: Molsof Salicylic acid = 3.0 gsalicylic acid 138.12 g / mol = 0.02172 The theoretical yield of aspiring can be calculated by: 0.02172 mols salicylic acid x 1 mol acetylsalicylic acid 1 mol salicylic acid x 80.16 1 mol acetylsalicylic acid = 3.91 g aspirin Theoretical yield = 2.3 g 3.91 g x 100 % = 59 % 11

Table 3: Quantitative results of crude and purified samples of salicylic acid and acetyl salicylic acid Compound Name Amount Collected (g) Melting Point Range ( ℃ ) Percentage Yield Crude Salicylic Acid 10.7 N/A N/A Purified Salicylic Acid 3.0 153-162 N/A Crude Acetylsalicylic Acid 10.7 N/A N/A Purified Acetylsalicylic Acid 2.3 136-140 59 % Table 4: Qualitative results for crude and purified samples of salicylic acid and acetyl salicylic acid Compound Name Colour Physical Description Crude Salicylic acid White with some yellow parts Pasty Pure Salicylic acid Clear Crystal like Crude Acetylsalicylic Acid White with some yellow Pasty Purified Acetylsalicylic Acid White Thin crystals Table 5: Quantitative results for Thin layer Chromatography (TLC) Compound Distance From Start Line (cm) Retention Factor (Rf) Pure Methyl Salicylate 5.1 1.0 Salicylic Acid 4.2 0.82 Acetylsalicylic Acid 4.3 0.84 Purified Salicylic acid 3.1 0.61 Purified Acetylsalicylic acid 3.8 0.75 Table 5 gives the determined retention factors for every sample that has been identified on the TLC plate. The solvent travelled 5.1 centimetres. The distances were 5.1, 4.2, 4.3, 3.1, and 3.8 cm for methyl salicylate, salicylic acid, acetylsalicylic acid, pure salicylic acid, and the acetylsalicylic acid generated, in that order. Calculating the retention factor is done by: Rf= Distance ¿ startingline ¿ theleading edge ( cm ) ¿ Distance the solvent travelled ( cm ) 12

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Example: Salicylic acid Rf= Distance ¿ startingline ¿ theleading edge ( cm ) ¿ Distance the solvent travelled ( cm ) Rf = 4.2 5.2 = 0.82 Figure 1: Thin Layer Chromatography Table 6: Qualitative Observation of Ferric Chloride test Compound Observation Acetylsalicylic Acid Light golden color Pure Salicylic acid Dark purple/ black Salicylic Acid Dark brown/ purple The ferric chloride test results for each tested chemical are displayed in Table 6. The colour of the produced acetylsalicylic acid was the same as the colour of the conventional acetylsalicylic acid, which was brown. The resulting refined salicylic acid's colour matched that of the conventional salicylic acid, which was a dark purple colour. The colours of the two created compounds coincided with those of the reference compounds. 13 1 2 3 4 5 Rf = 1.0 Rf = 0.82 Rf = 0.84 Rf= 0.61 Rf=0.75 1 - Pure Methyl Salicylate 2 - Salicylic Acid 3 - Acetylsalicylic Acid 4 - Purified Salicylic Acid 5 - Purified Acetylsalicylic Acid

Figure 2 : The salicylic acid's infrared spectrum, where the wavenumber is displayed versus transmittance percentage. The infrared spectrum of the salicylic acid generated during the experiment is displayed in Figure 2. The three most notable peaks are 3231.6019, 2843.9588, and 1654.9380. 14

Figure 3 : The Acetylsalicylic acid infrared spectrum, where the wavenumber is displayed versus transmittance percentage. The infrared spectrum of the acetylsalicylic acid generated during the experiment is displayed in Figure 3. The wavenumbers at which the most notable peaks are located are 2724.6840, 1748.1214, and 1677.3020. Table 6: Infrared Spectroscopy Absorption for Salicylic Acid and Acetylsalicylic Acid Compound Peaks (cm -1 ) Functional Group Salicylic Acid 3231.6019 Alcohol (O – H phenol) 2843.9588 O – H Carboxylic acid 1654.9380 C = O Carboxylic acid 15

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Acetylsalicylic Acid 2724.6840 O – H Carboxylic acid 1748.1214 C = O ester 1677.3020 alkene The peaks of the spectrums for salicylic acid and acetylsalicylic acid, along with the matching functional group at the wavenumber, are shown in Table 6. Discussion: Based on the calculations, 41% of the starting material was lost during the process, meaning that the actual yield of the product was 59% of the original amount. This considerable product loss could have been caused by several sources. The loss of product during the chemical transfer between containers is a crucial element that could have led to spillage or adhesion to container surfaces, lowering the yield overall. Additionally, contaminants that could have impacted the product's quality and chemical characteristics could have resulted from the unreacted salicylic acid present in the finished product. A compound's experimental melting point is given as a range. The temperature at which the compound's first liquid droplet is seen is recognised as the lower end of the melting range. The temperature at which the chemical purposefully melts is the upper limit of the melting range. Organic compounds that are impure have a lower melting point than their pure equivalent in addition to a wider melting range. Pure organic compounds have "sharp" melting points, which suggest that they would melt within a range of 1°C or less. The temperature for the produced salicylic acid is represented in table 3. The measures value was 153 ℃ - 162 ℃. The literary value for the melting point of Salicylic is 138 ℃. The experimental value of the melting point and the literal value show a difference of more then 1 ℃. Due to this the salicylic acid in impure. Adding on, the acetylsalicylic acid was pure. The observed melting range was 136 ℃ - 140 ℃. While the actual melting range is 136 ℃. The reason behind the somewhat broader melting range was because more sample than needed was sandwiched between the two watch lenses. This happens as a result of a compound's higher melting time for bigger samples. Impurities that were added to the substances when they were added to containers or transferred to new containers were the source of the disparity in the melting range for salicylic acid. 16

Table 5 retention factor analysis provides important information on the purity and similarity of the compounds. Similar retention factors imply that two chemicals might be the same, but they do not prove it. Here, the close retention factors for salicylic acid and purified salicylic acid after purification imply that they are comparable (0.82 and 0.84), suggesting that the purification procedure was successful. The manufactured type of acetylsalicylic acid may contain contaminants, though, as indicated by the difference in retention factors between it and regular acetylsalicylic acid. Also, each of the six distinct lanes only had one dot visible; the compounds are pure. A lane with a single dot would represent a pure compound, whereas a lane with many dots or a line would represent an impure compound. In addition to the ferric chloride test results, Table 6's colour observations offer more proof of purity. The ferric chloride test was the third experiment carried out on the produced compounds. Ferric chloride produces a distinctive colour shift in solutions containing phenols, enols, or other specific chemicals. Specifically, when a phenol group-containing chemical is combined with ferric chloride, the mixture takes on a purple hue. Purified salicylic acid, crude acetylsalicylic acid, and purified acetylsalicylic acid were used in the assay. The presence of a purple hue in the ferric chloride test, along with a dark purple colour in salicylic acid and refined salicylic acid, substantiates their identification as salicylic acid. By contrast, their brown hue and lack of purple colour in both the acetylsalicylic acid and the generated acetylsalicylic acid suggest their purity. Infrared spectroscopy was the last test that was performed on the substances. Because different wavelengths of radiation are absorbed by distinct functional groups in a material, an infrared spectrum graph is constructed for a chemical depending on its functional groups. Only the pure samples of salicylic acid and acetylsalicylic acid were used in this experiment. Figures 2 and 3 display the generated graphs. In salicylic acid, the O-H and C=O portions of the carboxylic acid functional group are represented by the peaks located at 2843.96 cm-1 and 1654.94 cm-1, respectively. The O-H phenol group at 3231.6019 cm-1 further supports its presence. The identification of salicylic acid is further supported by the alignment of these peaks with the reference spectra. 17

Finally, stoichiometry was used to compute the theoretical yields in order to determine the percent yield for both purified salicylic acid and acetylsalicylic acid. The results showed that the levels for acetylsalicylic acid were 2.3g and salicylic acid were 3.0g. The results of the percent yield calculation were 59% for acetylsalicylic acid. Since a mass is lost during multiple processes throughout the experiment, getting a yield near to 100% would not be feasible for this laboratory experiment. These processes include the moving of materials between containers, the crystallisation process, and the vacuum filtering process. Some mass is lost during these procedures because crystals remain in certain pieces of equipment, like glassware, as demonstrated by transfers of crystals from one piece of glassware to another and in the filter paper during vacuum filtration. To sum up, the integration of yield computations, melting point information, retention factor analysis, colour testing, and infrared spectroscopy offers a thorough comprehension of the product's identification, purity, and yield. It also illuminates possible areas of inaccuracy in the synthesis procedure. Conclusion Acetylsalicylic acid has a percent yield of 59%. The yield show that each chemical was produced in a respectable quantity. It is not feasible to raise these yields to levels above 90% due to mistakes made in the laboratory. The results of the tests, which included infrared spectroscopy, thin layer chromatography, ferric chloride test, and melting point analysis, showed that the acetylsalicylic acid and salicylic acid that were synthesised mostly pure. Thus, this lab experiment was successful. 18

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References 19

1. Aspirin. https://pubchem.ncbi.nlm.nih.gov/compound/Aspirin (accessed 2023-11-01). https://doi.org/10.1111/j.1440-1746.2010.06569.x. 2. astroenterology and Hepatology 2011, 26 (3), 426–431. https://doi.org/10.1111/j.1440- 1746.2010.06569.x. 3. Bele, A.; Khale, A. AN OVERVIEW on THIN LAYER CHROMATOGRAPHY. IJPSR 2011, 2 (2), 256–267. https://citeseerx.ist.psu.edu/document? repid=rep1&type=pdf&doi=974c337508d22ee7219c0cafb2ed4d4db2c1c630 4. Blumenrath, S. The Neuroscience of Touch and Pain. https://www.brainfacts.org/thinking-sensing-and-behaving/touch/2020/the-neuroscience- of-touch-and-pain-013020 (accessed 2023-11-01). 5. Chem 1111 Experiment 21 - Synthesis of Aspirin Postlab. https://www.uhscienceresource.com/chem1111-exp21-postlab (accessed 2023-11-01). 20

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