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During this lab the synthesis of trans-cinnamic acid occurs when heated and reacts with sulfuric acid. One test was conducted to determine if the experiment was successful. The test conducted was the analysis of the IR spectrum. The IR results determined that the experiment was successful and the product produced was methyl trans-cinnamate, which is a component of strawberry aroma.
Of the product formed, the percent yield was calculated to be 114.19%.
The intent of this laboratory experiment is to demonstrate the steps required for trans-cinnamic acid1 to react to become methyl trans-cinnamate, which is a component of strawberry aroma. The structure of the starting material of trans-cinnamic acid is shown below (Figure1). This experiment builds on previous techniques learned, such as IR spectra skills and rota-vap skills.
IR spectrum2 allows for the detection of specific functional groups within compounds. The IR bands that are expected to be present for trans-cinnamic acid are carbon double bonded to oxygen, a carbon double bonded to another carbon, and alcohol group.
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The IR results for the product methyl trans-cinnamate shows the presence of all of the bonds of the starting product trans-cinnamic acid but has a methyl group bonded to the oxygen instead of a hydrogen in the alcohol in the starting product.
Rota-vap is the common name for a rotary evaporator.3 Rota-vaps use temperature fluctuations to control the rate of evaporation and allow the solution to not freeze, the solution is evaporated in a vacuum condenser. Due to the vacuum condenser, the temperature required to evaporate the solution is much lower than would otherwise be required.
Because the solution is rotating, the rate of evaporation is significantly faster than it would be if it were to remain stationary.
A Fischer esterification4 reaction involves carboxylic acids, an alcohol, and must occur under acidic conditions. In order for the reaction to occur the system must be heated and the acidic conditions act as a catalyst. Due to the nature of the reaction, Fischer esterification is a common reaction when synthesizing amino acids.
Compound: Trans-Cinnamic Acid
Compound: Methanol
Compound: Tert-Methyl Butyl Ether
Compound: Sulfuric Acid
Compound: Sodium Chloride
Compound: Sodium Bicarbonate
Compound: Methyl Trans-Cinnamate
Compound: Sodium Sulfate
Preparation of methyl trans-cinnamate. Unless stated otherwise, the chemicals used to perform this experiment were obtained through a supplier and used as received. In a 15-milliliter round-bottom flask, 200 milligrams of phenacetin and 3 milliliters of methanol were placed with a magnetic stir bar. The contents were stirred until the solid was dissolved and then 3 drops of concentrated sulfuric acid was added. Once the sulfuric acid was added, a microscale condenser was attached, and the system was heated on medium heat setting for one hour (Figure 2). After one hour remove the system from heat and allow to cool to room temperature. Once cooled, transfer the solution to a test tube labelled “organic”. Wash the round-bottom flask with tert-butyl methyl ether (BME).
To the liquid in the test tube, slowly add 3 milliliters of 5% sodium bicarbonate (NaHCO3) in 15% sodium chloride (NaCl) solution (bubbling with occur due to CO2 formation). Once the bubbling stops add the BME washing from the round-bottom flask and shake several times. Layers will form and settle. Remove the bottom layer (aqueous) with a Pasteur pipet and transfer to another test tube labelled “aqueous”. Using the removed aqueous layer, add 3 milliliters of BME to extract any remaining organics and remove aqueous layer. Combine the two organic layers and wash them with 3 milliliters of a saturated NaCl aqueous solution. Layers will form, once they settle remove the lower (aqueous) layer. Dry the organic layers by adding anhydrous sodium sulfate (Na2SO4) little by little, until it no longer clumps together at the bottom of the test tube. Decant the solution into a tared round-bottom flask, leaving only the solid in the test tube. Evaporate the solvent in a rota-vap (Figure 3). Weigh the flask with the product and obtain IR spectra of the product.
The structure of the product produced by the method involving the reflux apparatus is shown below (Figure 4). The starting mass of trans-cinnamic acid was 0.224 grams and the final product weight was 0.25 grams. There was possible product loss while inverting the test tube. This may have occurred due to some of the product leaking out of the cap of the closed test tube.
The percent yield was calculated to be 114.19%. While there obviously cannot be a percent yield greater than 100% because it is not possible to end up with more product than there was in the beginning, it is apparent that there was an error within the experiment. A reasonable conclusion to the excess “product” weight is that some of the sodium sulfate was not evaporated out remained in the solution.
A possible yield increase if Le Chatelier’s principle7 was used. Le Chatelier’s principle is if you remove either a product or reactant it will shift the equilibrium to the desired side and force the reaction to go to completion until all the reactants are used. If the amount of alcohol used was increased, then the reaction would be driven to the right and an increase of products would occur.
When comparing the gathered IR results to the known and accepted IR results, most of the peaks occurred in the general vicinity that they were expected to. There were peaks at 3082 cm-1, 2825 cm-1, and 1672 cm-1. The only peak that was missing was 1717 cm-1, which indicated the absence of carbon double bonded to an oxygen.
Due to the IR results, it is reasonable to conclude that the product obtained was methyl trans-cinnamate due to the fact that the observed IR bands were very similar to the expected IR bands. The only peak that was missing was in between two of the anticipated bands. There was over a 100% yield, which indicated that the product was not pure. The final product appeared to be oily and smell similar to artificial strawberry.
Only one test was conducted to determine the accuracy of the experiment. However, the test neither confirmed nor denied that the results were accurate. The test conducted was IR spectra. A majority of the peaks of the observed spectra from the obtained product matched the peaks of the know IR spectra of methyl trans-cinnamate. Being that the only peak that did not align but fell within the range of two other known peaks it is a reasonable assumption to conclude that the experiment was successful and methyl trans-cinnamate was formed during the reaction. Although being that only one test was conducted, it would be a wise decision to conduct other tests such as NMR or melting point to determine the accuracy of the results and to determine with certainty whether the experiment was successful.
From Trans-Cinnamic Acid to Strawberry Aroma: Synthesizing Methyl Trans-Cinnamate. (2024, Feb 16). Retrieved from https://studymoose.com/document/from-trans-cinnamic-acid-to-strawberry-aroma-synthesizing-methyl-trans-cinnamate
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