Chem formal lab report final

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Chemistry

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Feb 20, 2024

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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

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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