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Assignment 6 - lab work
Organic Chemistry Lab II (CHEM201401)
Boston College
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Discussion 6
In this experiment, esters were synthesized in two different ways. In the first part of the experiment, cholesteryl benzoate was synthesized by reacting cholesterol with benzoyl chloride in a pyridine solution. Also, observations were made on its liquid crystal properties. When benzoyl chloride was added to the solution of pyridine and cholesterol, the solution was white, cloudy, and hot. This is due to the reaction between the starting materials to make the product, cholesteryl benzoate. After a few seconds, the solution became solid and when methanol was added, the solid started to break up. This can be due to the solubility of the product with methanol. After recrystallization, the crystals were white and shiny. The product then was observed for its liquid crystal properties, because of its chirality center and organization, through heat and light. There was a shimmer of colors, prism-like, however, the color that was most seen was blue. The reason why there was color reflected was because at liquid crystal phase, the crystals are ordered in which whatever light was shown through, it will be reflected. The percent yield of cholesteryl benzoate was 7%. The percent yield was low because two vacuum filtrations had to be done and recrystallization, so the product may have been lost in these steps due to transfers. The melting point of the mixture was 127.9-132ºC. The melting point of the purified product was 149.3-150ºC. The literature melting point is 149-150ºC. This indicated that the purified product was pure and left of no to little impurities. The melting point of the mixture was significantly lower than the purified because of impurities. This can be due to different crystal structures in the products and how they react with each other under heat. Also, any disruptions in the product (such as impurities) can cause the product to have a lower melting point. In the second part, acetylsalicylic acid was synthesized by the esterification of salicylic acid with acetic anhydride and phosphoric acid. Solubility of the product was also tested. When
Discussion 6
the starting materials with the catalyst was added, a yellow solution was formed. With the addition of deionized water, the yellow color disappeared. This is because any unreacted acetic anhydride reacted with water which in turned caused the color to disappear. Addition of more water turned the solution white. The crystals were white and flakey. The percent yield of acetylsalicylic acid was 54% because product may have been lost in transfers and recrystallization. The melting point for acetylsalicylic acid was 138.1-139ºC. The literature melting point is 138-140ºC. This meant the product was pure. The melting point for commercial aspirin was 138.5-141ºC. The commercial aspirin had a different melting point because there are impurities mixed in with the aspirin since both products contain the same starting material. Solubility tests were used for both the commercial and purified product. For the purified, in toluene, hot water, rubbed glass rod, and hydrochloric acid, it was not soluble. In sodium hydroxide, it was soluble. For the tablet, toluene and hot water resulted in no solubility. This is due to the non-polar covalent bonds in the aspirin. To dissolve the aspirin, it must dissolve in non-polar solutions. In the third part, ferric chloride was used to test for phenols in solutions of aspirin product and salicylic acid. For salicylic acid, it turned pale yellow. This indicated no phenol groups. For the crude and purified product, it turned light and dark purple, respectively. However, this meant that there was unreacted starting material because there is no phenol group in the crude product but it still turned purple (lighter purple). This indicated phenol is present. However, for test tube 3, the purple was lighter than test tube 4. Also, when test tube 4 was put into a water bath, the materials were soluble, but for test tube 3 and 2, there was insolubility.
Assignment 6 - lab work
Course: Organic Chemistry Lab II (CHEM201401)
University: Boston College
