Abstract
The purpose of this experiment was to determine if reacting an acid with an alcohol produced an ester. In this experiment the carboxylic acid of acetylsalicylic acid was esterified by methanol and produced methyl salicylate (oil of wintergreen).1 Thin layer chromatography and infrared spectroscopy were utilized in determining that the liquid collected was in fact an ester.
Introduction
An ester is an organic compound formed through the process of esterification, which involves the reaction of an alcohol and an organic acid. Esters are common derivatives of carboxylic acids and also constitute an important functional group family of their own. Esters are produced on a large scale commercially, as they are known for their flavoring and fragrance of many fruits, flowers, artificial flavors, and perfumes. Esters are responsible for the sweet taste and smell of common items such as bananas, oranges, pineapples, apples, and rum. Esters are also used commercially as solvents, plasticizers, starting materials for polymers, as well was pharmaceuticals.1
Methyl salicylate, otherwise known as oil of wintergreen, is an ester with a characteristic wintergreen aroma. Oil of wintergreen was originally produced naturally from the wintergreen plant and Black Birch. Now oil of wintergreen is synthetically produced for medical purposes and used for flavoring teas, which aids in soothing muscles, headaches, and other pains. Oil of wintergreen can only be consumed in very small amounts in products, as it is a volatile and toxic substance, requiring only 6mL to kill an adult human.
In this lab, methyl salicylate was prepared from previously synthesized aspirin. The organic acid used in the esterification was acetylsalicylic acid and was reacted with methanol, an alcohol. A mixture of refluxing, separation, and rotary evaporation techniques were utilized in this lab to obtain methyl salicylate. The prepared oil of wintergreen was then analyzed by thin layer chromatography (TLC) and infrared spectroscopy.
Experimental:
On the first day of experimentation refluxing was conducted. 1.4905g of previously prepared aspirin (acetylsalicylic acid) was transferred into a 50-mL round bottom flask. Next, 5mL of methanol was added to the flask, along with 10 drops of concentrated sulfuric acid (H2SO4). A water-jacketed condenser was attached to the flask, and the flask was then placed into the well of the heating mantle.
The contents were heated, with stirring, and allowed to reflux for 90 minutes. The mixture was then allowed to cool to room temperature after refluxing was completed. The mixture was then prepared for separation and was transferred into a separatory funnel. 10mL of saturated, aqueous sodium bicarbonate was added to the separatory funnel, along with 10mL of dichloromethane (DCM). The funnel was closed and vigorously shaken with periodic releasing of gas buildup for about 3-4 minutes.
The layer were allowed to separate in the funnel for about 2 minutes, and the lower organic layer was collected in a 50mL Erlenmeyer flask. The sodium bicarbonate and DCM wash was repeated a second time. 2 small scoops, approximately 1g, of anhydrous sodium sulfate were added to the flask containing the organic layer for drying. The flask was then sealed tightly with parafilm and stored. On the second day of lab the organic solution was decanted from the sodium sulfate, into a pre-weighed round bottom flask.
The organic solution was further dried by removal of solvent by the rotary evaporation machine, and was re-weighed. The organic solution was then analyzed by IR spectroscopy using the FITR machine in lab. Thin Layer Chromatography analysis was also conducted on day 2 of this lab. Aspirin given by the instructor was dissolved in 1:1 ethanol dichloromethane solution and was spotted on a TLC plate with a toothpick. The collected organic solution was also spotted on the TLC plate with the aspirin. The TLC plates were then placed into a developing chamber constructed out of a 50mL beaker that contained about 2mL of 3:1 hexane:ethylacetate developing solution.
Results & Discussion:
Reaction:
Scheme 1: The reaction of acetylsalicylic acid and methanol yield methyl salicylate, an ester. For this experiment 1.4905g of acetylsalicylic acid was used, and the theoretical amount of methyl salicylate expected from this experiment was 1.2588g. This experiment yielded 0.9839g of methyl salicylate, making the percent yield for this experiment 78.16%. The yield could have been improved by refluxing the solution for longer, allowing it more time to react and form product. Also some product was lost due to the beaker not being covered immediately after oil of wintergreen was collected.
Compound| Distance Solvent Front Travelled (cm)| Distance Component(spot) Travelled (cm)| Retention Factor(Rf)| Aspirin (Spot #1)Apsirin (Spot #2)Aspirin (Spot #3)| 5.55.55.5| 0.51.11.3| 0.090.200.24| Oil of Wintergreen (Spot #1)Oil of Wintergreen (Spot #2)| 5.55.5| 0.91.4| 0.160.25| Table.1: Thin Layer Chromatography Analysis.
Table 1 displays the TLC analysis of aspirin and oil of wintergreen. The table displays the distance the solvent front travelled up the TLC plate as well as the distance each component of each compound travelled. The Rf value of the first spot of the oil of wintergreen did not match any of the values for the aspirin, but was located between the first and second spot of the aspirin. The second spot created by the oil of wintergreen travelled 0.1cm further than the third spot created by the aspirin, and there is only a 0.01 difference in the Rf values.
The IR spectra obtained from the oil of wintergreen clearly displayed an alcohol group at 3416cm-1. The alcohol group displays a very strong and broad peak. At 2360cm-1 a medium peak is seen that represents the carboxylic acid present in methyl salicylate. A medium peak is also present at 1676cm-1, representing carbon double bonded to an oxygen atom. A carbon bonded to an oxygen atom of the ester functional group is displayed in the IR spectra as a medium/short peak at 1251.58. All functional groups that were expected to be found in oil of wintergreen were found on the IR spectra.
Conclusion
With the percent yield of this experiment being 78.16%, there was more than enough product collected to carry out the functionality group, IR testing, and thin layer chromatography analysis. The TLC analysis displayed that while aspirin and oil of wintergreen both contained similar components, aspirin contained one more component showing that something other than aspirin was synthesized in lab. The IR spectra further confirmed that the expected characteristic functional groups of methyl salicylate were present in the synthesized substance, and proved the product synthesized in this experiment was indeed oil of wintergreen.
References
1. Hill, Richard, and Barbaro, John. Experiments in Organic Chemistry. 3rd ed. Raleigh: Contemporary, 2005. Print.