Ester Synthesis And Analysis: Aspirin and Oil of Wintergreen. Vanessa Jones November 19, 2015 Thursday 8:30 Lab Section Lab Partner: Melissa Blanco

Transcription

1 Ester Synthesis And Analysis: Aspirin and Oil of Wintergreen Vanessa Jones November 19, 2015 Thursday 8:30 Lab Section Lab Partner: Melissa Blanco

2 INTRODUCTION For this lab, students attempted to synthesize two organic esters, to study the implications of reactions which do not go to competition, and to use chromatographic techniques to evaluate the purity of the products. This experiment was designed to reach these goals because it provides two different esters to synthesize, aspirin and oil of wintergreen, and gives various techniques to test the purity of the products produced for each ester. Heat was added to carboxylic acid and alcohol to produce and ester and water. Aspirin: heat C 7 H 6 O 3 + C 4 H 6 O 3 à C 9 H 8 O 4 +H 2 O Oil of Wintergreen: heat C 7 H 6 O 3 + CH 4 O à C 8 H 8 O 3 +H 2 O Aspirin is a very common drug that can be used to treat many symptoms. Aspirin is most commonly used as a drug to treat pain, fever, arthritis and inflammation. It can also be used to lower risk of heart attack in some patients and can even be used to lower risk of a stroke reoccurring. It is a very important and globally used drug. (Anonymous, a 2012). Oil of wintergreen, an ester that is produced naturally by many plants, is used as an antiherbivore defense. It works by attracting beneficial insects and killing herbivorous insects. It is also used as a pheromone to warn other plants of certain pathogens. (Anonymous, b 2015). Salicylic acid was used in two reactions to synthesize oil of wintergreen and aspirin. In the Acetylsalicylic acid, or aspirin reaction, salicylic acid and acetic anhydride react to produce small white crystals of aspirin. This is possible because of the alcohol properties of the salicylic acid and the carboxylic acid properties of acetic anhydride. An alcohol is an organic molecule that contains the grouping C-OH.

3 The same concept is present in the reaction between salicylic acid and methanol, producing a clear liquid, oil of wintergreen. The carboxylic acid properties of Salicylic acid and the alcohol properties of methanol cause the methanol to break apart and attach to a hydrogen in the salicylic acid. There are two different chemical methods used to test for purity in this lab. The first is chemical separation by thin layer chromatography. This is where a TLC, or thin layer chromatography, plate is used. This is the stationary phase of the reaction. The solutions produced are spotted on this plate and the plate is placed in a beaker with a mixture of hexane and ethyl acetate. This mixture is the mobile phase of the reaction. Depending on the polarity, one substance will move faster and the other will move slower because one is attracted to the mobile phase and one is attracted to the stationary phase. Next a UV lamp is used to examine where the spots end up and so the distances could be measured. The other way of testing for purity in the lab is to use chemical separation by high pressure liquid chromatography. This is where a pump pushes the mobile phase solvent through a stationary phase column. This column has small polymer beads and they attract different molecules based on their polarity. If a material

4 passing through the column is more attracted to the stationary phase takes longer to pass through this column. After exiting the column, the compounds flow with the mobile phase to a detector can measure UV light absorbed. This is represented in a chromatogram and each peak on the chromatogram is the retention time. This allows the purity of the sample to be found. EXPERIMENTAL First, a large test tube was obtained and labeled g of salicylic acid was measured. Two ml of methanol were then added to the test tube and 15 drops of concentrated sulfuric acid were added as well. Afterwards the test tube was loosely stoppered with a cotton plug and swirled until the starting material was fully dissolved. The test tube was then placed in a bath to be heated for 30 minutes. The test tube must be swirled periodically throughout the 30 minutes to help the solution be dissolved quicker. After the 30 minutes the test tube was removed from the hot bath and two ml of cold distilled water were added and the contents were mixed. The oil of wintergreen was then extracted by adding three ml of methylene chloride and inverting the test tube several times. The test tube was then left to stand until the layers were separated. A Pasteur pipet was then used to draw up the lower layer to be transferred into a clean, dry test tube. Repeat the extraction process to add a second methylene chloride layer to the new test tube. The combined layers were then dried by adding a small amount of anhydrous sodium sulfate. The methylene chloride layer was then poured into a clean, dry sample vial, leaving the sodium sulfate behind and the vial was stoppered with a cotton plug. This sample vial was then turned into the instructor to be stored until next week. For the aspirin part of the lab, first a test tube was obtained and labeled g of salicylic acid was measured and transferred to the labeled test tube. Next, 25 drops of acetic

5 anhydride were added to the test tube, along with two drops of concentrated phosphoric acid. The test tube was then stoppered with a cotton plug and swirled until the starting material was fully dissolved. The test tube was then placed in a bath to be heated for ten minutes. Swirling until the starting material is fully dissolved is an important step because my group placed the test tube in the water to boil before the starting material was fully dissolved and had to redo this step. After ten minutes, the test tube was removed from the bath and two ml of cold distilled water were added. Next three more ml of distilled water were added, and the solution was swirled to mix. White crystals of aspirin began to form and the test tube was placed in an ice bath for ten minutes to allow the crystals to be fully formed. Next a side-arm flask and Büchner funnel were set up so the resulting solution could be filtered. The test tube was poured into the funnel and cold distilled water was added in order to extract all the contents. After all the solution was poured into the funnel two portions of three ml distilled water were added to the funnel and then air was pulled through. Next the solid was transferred into a clean, dry labeled sample vial and stoppered with a cotton plug. Finally, the vial was given to the instructor to store until next week. For week two, first the sample vials containing our products were obtained. The cotton plug was removed and the mass of each vial was taken and the mass of each product was calculated. Next the percent yield for each compound was calculated using previously found theoretical yields. Next a small amount of the aspirin was dissolved in 2 ml of a mixture of ethanol and water. This was repeated in a test tube with a small amount of salicylic acid starting material. This was then repeated again in a third test tube with a small amount of pure acetylsalicylic acid. Next, ten drops of 1 M iron chloride was added to each test tube.

6 Three test tubes were prepared, one with four drops of the experimental wintergreen, one with four drops of pure methyl salicylate, and one with a very small amount of salicylic acid. Two ml of methanol were added to each test tube and each test tube was swirled to mix and dissolve the sample. 5 ml of the TLC solvent was then placed into a 250 ml beaker and a piece of folded filter paper was placed in the beaker. The beaker was then covered with aluminum foil and swirled so the beaker could be saturated with its vapors. A TLC plate and three spotters were obtained. Three spots were marked in the TLC plate and these spots were labeled. The substances in the test tubes were then spotted onto the TLC plate. The TLC plate was then placed in the beaker until the solvent front reaches 0.5 cm from the top of the plate. The plate was then placed on a paper towel until dry. Next the TLC plate was placed under a UV lamp and the glowing spots observed were traced. Finally, a few grains of experimental aspirin were dissolved in a solution of 10 ml of methanol. The sample was then injected onto the chromatograph. The chromatogram observed was very similar to the one provided by the instructor, meaning we had the right ratio of experimental aspirin. RESULTS Table 1: Data Collected for Aspirin (Acetyl Salicylic Acid) Production Sample Calculations (Percent Yield): Theoretical yield: Acetyl Salicylic Acid à g x 1 mol x 1 mol x g = g g 1 mol 1 mol Percent yield: Experimental yield x 100 = g x 100 = %

7 Theoretical yield g Table 2: Data Collected for Oil of Wintergreen (Methyl Salicylate) Production Table 3: Qualitative test for Salicylic acid with Fe 3+ Table 4: Distances Traveled by Spots and Solvent Front and Calculated Retention Factors Sample Calculations (Retention Factor): Methyl Salicylate à Distance Traveled by Compound = 3.4 cm = 0.59 Distance Traveled by Solvent Front 5.8 cm Figure 1: TLC Plate Sketch

8 Figure 2: Experimental High Pressure Liquid Chromatography Graph Figure 3: Standard High Pressure Liquid Chromatography Graph

9 Table 5: HPLC graph data DISCUSSION The objective of this experiment was to study the implications of reactions which do not go to competition. This was done by synthesizing two organic esters then evaluating the purity of the products. The objective of the experiment was achieved by collecting information to calculate the percent yields of the aspirin and oil of wintergreen. The goal was to have a high percent yield, meaning the product was extremely pure, but this proved difficult because of all the errors that could have taken place. The percent yield was used to answer the experimental

10 question because it showed the purity of the product and therefore proved weather or not the reaction went to completion. The results of the experiment show that neither reaction went fully to competition. This conclusion is reached based on the following data, the percent yield calculated for the aspirin produced was 74.19% and for oil of wintergreen was 75.16%. The aspirin crystals produced were a white powdery paste and the oil of wintergreen was a clear liquid with a very strong mint scent. The retention factors for wintergreen and methyl salicylic acid were the same, meaning the wintergreen produced was impure. Because the peak for unreacted salicylic acid in the experimental high pressure liquid chromatography graph is much smaller then the peak for aspirin, the reaction was relatively pure. This shows there was only a very small amount of unreacted salicylic acid leftover. The findings here agree well with expected values. Expected results were that the products produced wouldn t be completely pure because of possible errors that could have occurred. Around 75% is a very good purity for products of a reaction and even through the wintergreen wasn t completely pure its extremely difficult to produce a product with that amount of purity. The peak for unreacted salicylic acid in the experimental graph was very small meaning only a small portion didn t react. The results here show that neither reaction went fully to competition based on the percent yields calculated for each product.

11 REFERENCES 1.) Anonymous, a "Aspirin (By Mouth)." National Center for Biotechnology Information. U.S. National Library of Medicine, Web. 06 Dec < 2.) Anonymous, b "Methyl Salicylate." Wikipedia. Wikimedia Foundation, 2 Nov Web. 06 Dec <