synthesis of aspirin, Schemes and Mind Maps of Chemistry

Download synthesis of aspirin and more Schemes and Mind Maps Chemistry in PDF only on Docsity! Los Angeles City College Chemistry 51 Fall 2005 3093 1 Experiment 11 Synthesis and Analysis of Aspirin INTRODUCTION Aspirin is most widely sold over-the-counter drug. It has the ability to reduce fever (an antipyretic), to reduce pain (an analgesic), and to reduce swelling, soreness, and redness (an anti-inflammatory agent). One of the first recorded accounts for the discovery of aspirin appeared in England, in 1763, crediting the bark of willow trees with a beneficial effect in alleviating distress due to fevers, aches, and pains. Later, the compound salicylic acid (named for the Latin word for willow, salix) was isolated from willow bark. It proved to be the active ingredient. By 1860, organic chemists were able to synthesize salicylic acid from basic starting materials, this furthered the therapeutic use of the substance, but there were problems. Salicylic acid proved to be irritating to the membranes of the throat, mouth, and stomach. These problems are directly associated with the high acidity of the compound, but a simple remedy was discovered, namely, replacement of the acidic phenolic hydrogen atom with an acetyl group. When interpreting the structures of the above organic compounds, note the following characteristics of these molecules. Organic molecules are complex compounds of carbon. Carbon always shares four pairs of electrons in bonds with other molecular groups or atoms. When the structure of an organic molecule is drawn using the condensed method, carbon rings are represented with simple geometric shapes, such as a hexagon. Each corner of the hexagon represents a carbon atom and the number of hydrogen atoms required to share 4 pairs of electrons with the carbon. If the “corner” has no other marks, that means there is a carbon atom bonded to 2 other carbon atoms (in the ring) plus 2 hydrogen atoms. The hydrogen atoms are implied, not show. If a carbon to carbon double bond (C =C) is present and the carbons are attached in a ring, each of the two carbon atoms is bonded to two others with 6 pairs of electrons, and only one hydrogen is attached to each of these carbons give the full compliment of four bonds. If a triple bond is present then only one other atom may be attached. Check the structures below to see that each carbon has four and only four bonds. Oxygen, on the other hand, will bond covalently to only two atoms, and hydrogen bonds to only one. A useful synthesis of acetylsalicylic acid was developed in 1893, patented in 1899, marketed under the trade name of “aspirin” by the Bayer Company in Germany. The name aspirin was invented by the chemist, Felix Hofmann, who originally synthesized acetylsalicylic acid for Bayer. More than 50 million 5-grain tablets of aspirin are consumed daily in the United States. In Part I of this experiment, you will prepare aspirin by reaction of salicylic acid with acetic anhydride, using concentrated sulfuric acid as a catalyst. Los Angeles City College Chemistry 51 Fall 2005 3093 2 Aspirin still has its side effects. Note that the carboxylic acid functional group remains intact. This may result in hemorrhaging of the stomach walls even with normal dosages. The acidic irritation can be reduced through the use of buffering agents, like antacids, in the form of magnesium hydroxide, magnesium carbonate, and aluminum glycinate when mixed with aspirin (Bufferin). While the ester can be formed from acetic acid and salicylic acid, a better preparative method uses acetic anhydrides in the reaction instead of acetic acid. An acid catalyst, like sulfuric acid or phosphoric acid, is used to speed up the process. Part I: Synthesis of Aspirin Caution! The preparation of aspirin involves the use of two very hazardous materials - concentrated sulfuric acid and acetic anhydride. Proceed only if you have a fume hood to work in, and after you have listened carefully to the instructor’s safety directions. As usual, goggles must be worn at all times. PROCEDURE 1. Weigh 4.0 g (0.030 mol) of salicylic acid in a 125 mL Erlenmeyer flask. Using this quantity of salicylic acid to calculate the theoretical yield of aspirin. Record the weigh on the report sheet. 2. Carefully add 6 mL (0.051 mol) of acetic anhydride to the flask. (CAREFUL! Acetic anhydride is irritating to the skin and eyes.) 3. Using extreme caution, add 5 drops of concentrated sulfuric acid to the flask, swirl gently, and place the flask in a beaker of boiling water. Clamp the flask to a ring stand and heat for 20 minutes. Constantly stir with a glass rod; the entire solid must completely dissolve. 4. Remove the flask from the boiling water bath and allow to cool to room temperature. Crystallization should occur during cooling. If crystals begin to grow, let the flask sit undisturbed until crystals stop growing then add the 40 mL of ice water. If crystals do not grow, slowly pour the solution into a 250-mL beaker containing 40 mL of ice water, mix thoroughly, and place the beaker in ice water and let sit undisturbed until crystals have grown. The water destroys any unreacted acetic anhydride and will cause the insoluble aspirin to precipitate out of solution. 5. Collect the crystals by vacuum filtration (using a Buchner funnel, if available). 6. Wash the crystals with two 10-mL portions of cold water followed by one 10 mL portion of cold ethanol. Allow the crude product to dry, then weigh it on the rough balance. Los Angeles City College Chemistry 51 Fall 2005 3093 5 Experiment 10 ACID/BASE TITRATION Scientist Partner(s) REPORT SHEET Part I 1. Theoretical yield: g salicylic acid ( acid salicylic g 138 acid salicylic mol 1 )( aspirin mol 1 acid salicylic mol 1 )( aspirin mol 1 aspirin g 180 ) = g of aspirin (Theoretical yield of aspirin) 2. Experimental yield: Weight of aspirin & watch glass g Weight of watch glass g Mass of crude product obtained after suction filtration g Percent Yield of crude product ( yield ltheoretica yield alexperiment 100%) % Mass of re-crystallized product (optional) g Percent Yield of re-crystallized product ( yield ltheoretica yield alexperiment 100%) % Part II Melting Point of crude product (1st trial) °C (2nd trial) °C Melting Point of re-crystallized product (1st trial) °C (2nd trial) °C Ferric Chloride Test (Purity test) SAMPLE COLOR INTENSITY Salicylic acid Your aspirin Commercial aspirin Los Angeles City College Chemistry 51 Fall 2005 3093 6 QUESTIONS 1. What is the purpose of the 18 M sulfuric acid in the preparation of aspirin? 2. Explain why the percent of your aspirin was different from the results obtained from the commercial aspirin. 3. Old aspirin exposed to moisture often smells like acetic acid (vinegar). When aspirin is heated in boiling water, it decomposes and gives off a vinegar smell. The resulting solution gives a positive FeCl3 test. Why is this test positive? Write the chemical equation for the reaction of aspirin and water at high temperatures. 4. You have spent about 12 weeks learning about chemistry and its respective laboratory techniques. The typical street-drug producer usually doesn’t have any chemistry background but instead simply mimics the synthesis learned from another person or, in some cases, a book. If you take this into consideration along with your success at producing aspirin, how well do you trust the producers of street drugs to make drugs safe for consumer use?