3. Depending on how far your conversion of aspirin (acetylsalicylic acid) to oil
ID: 1081020 • Letter: 3
Question
3. Depending on how far your conversion of aspirin (acetylsalicylic acid) to oil of wintergreen (methyl salicylate) proceeded, any of the four compounds shown below could be present (starting material, two possible intermediates, and product). If the reaction mixture were simply filtered and concentrated, the crude product could be contaminated by any of the other three compounds OH OH methyl acetylsalicylate oil of wintergreen acetylsalicylic acid salicylic acid The reaction work-up you performed involved a series of extractions using dichloromethane and aqueous sodium bicarbonate. At the end, the combined organic extracts were dried, filtered and concentrated to provide your crude oil of wintergreen product. a) (4 points) This extraction procedure would not separate all of the possible impurities from your desired product. Identify which compound(s) would not be extracted away from your product by the procedure above b) (6 points) Propose a revised extraction protocol that should separate the compound(s) identified in a) away from your desired oil of wintergreen product, and allow you to isolate pure oil of wintergreen.Explanation / Answer
The objectives of this experiment were to synthesize two organic esters, study the implications of reactions, which do not go to completion, and use chromatographic techniques to evaluate the purity of the products.
Carboxylic Acid + Alcohol Ester + Water
Salicylic acid treated with acetic anhydride to get aspirin and water as byproduct. While the acetyl salicylic acid treated with methanol to give the intermediate methylacetylsalicylate which is to give the oil of wintergreen. This is Organic reactions and the solutions of reaction mixture contain various products and byproducts. It can be carried out in two step reactions. The final products of these syntheses were evaluated for purity with a chemical test for salicylic acid and the use of two chromatographic techniques – thin layer chromatography and highpressure liquid chromatography and gas chromatography mass spectroscopy.
In thin layer chromatography, compounds in mixtures are separated between the stationary phase (the TLC plate) and the mobile phase (the solvent: a mixture of hexane and ethyl acetate) due to differing polarities. With this test, ratios of fronts of the experimental product are calculated and compared to controls to determine its purity. The traditional organic reaction filtration involves TLC method followed by Column chromatography by using soluble organic solvents according to the compostion of the reaction. The byproduct of the reaction is also water that can be removed while washing with aqueous layer of sodium bicarbonate.
Hence the acetyl salicylic acid and methyl acetylsalicylate and desired wintergreen product are organic and can be dissolved in organic medium. Thus those compounds can not extracted with traditional filteration technique and might be present along with desired product.
These modern techniques can be used to see how much the reaction has been converted to pure compound or most of the desired compound and can be performed while the reaction proceeds.
To conduct high-pressure liquid chromatography, a few grains of experimental aspirin were dissolved in five to ten mL of methanol in a sample vial. This solution was injected onto the chromatograph .The resulting chromatogram was compared to that of the standard sample. The retention times and areas for aspirin and salicylic acid peaks were recorded. Using known concentrations and measured areas from the standard chromatogram and the measured areas from the experimental chromatogram, the concentrates of aspirin , salicylic acid and desired product in the sample were calculated.
Thus, after the identification of pure desired compound or the complete conversion of desired compound the other impurities may be very small amount in numbers. These can be removed by traditional organic separation to get the desired pure product. The difference with TLC and Instruments is the accurate or possible completion on results can be obtained in latter technique. Hence it would be useful.
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