experiment on synthesis of asprin, Schemes and Mind Maps of Chemistry

Download experiment on synthesis of asprin and more Schemes and Mind Maps Chemistry in PDF only on Docsity! 1 Aspirin is the common name for the compound acetylsalicylic acid, widely used as a fever reducer and as a pain killer. Salicylic acid, whose name comes from Salix, the willow family of plants, was derived from willow bark extracts. In folk medicine, willow bark teas were used as headache remedies and other tonics. Nowadays, salicylic acid is administered in the form of aspirin which is less irritating to the stomach than salicylic acid. To prepare aspirin, salicylic acid is reacted with an excess of acetic anhydride. A small amount of a strong acid is used as a catalyst which speeds up the reaction. In this experiment, phosphoric acid will be used as the catalyst. The excess acetic acid will be quenched with the addition of water. The aspirin product is not very soluble in water so the aspirin product will precipitate when water is added. The synthesis reaction of aspirin is shown below: Since acetic acid is very soluble in water, it is easily separated from the aspirin product. The aspirin isolated in this step is the “crude product”. A “purified product” can be obtained through recrystallization of the crude product in hot ethanol. In this experiment, the crude product will be the desired product. The percent yield of the crude product will be determined for this reaction. The purity of the product will also be analyzed. The product will be analyzed by three different methods: melting point, titration, and spectroscopic assay. The melting point range of pure aspirin is 138-140 C and the melting point range of the salicylic acid starting material is 158-161 C. If impurities are present in your crude sample, the melting point range for your product will be lower than the range of pure aspirin. Also, your melting point range may be greater than 2 degrees. From the titration of your sample, the moles of acetylsalicylic acid present can be determined assuming that there is not a large percentage of an acid impurity present in your crude sample. H3PO4 102 g/ mol d = 1.08 g/mL 138 g/mol 180 g/mol Aspirin Synthesis Experiment 5 2 The spectroscopic analysis of aspirin will involve the complexing of iron(III) to the deprotonated form of salicylic acid (salicylate ion) to give a purple solution. Only the salicylate ion complexes to iron(III). Your aspirin product as well as a commercial aspirin tablet will be compared to a standard 0.15% ferric- salicylate solution. In the presence of moisture, aspirin may decompose (hydrolysis) into salicylic acid and acetic acid. This reaction is the reverse of the synthesis reaction. The maximum allowable amount of free salicylic acid in an aspirin sample is 0.15% salicylic acid. Equipment and Reagents First Period Salicylic acid buret clamp burner Acetic anhydride stand with iron ring distilled water 85% phosphoric acid wire gauze ice bath 50 mL flask beaker of tap water filter paper Büchner funnel aspirator Second Period Shell Vial melting point apparatus capillary tubes Third Period 125 mL Flask phenolphthalein indicator buret 0.1 M NaOH mortar and pestle aspirin tablets Forth Period 3 x 50 mL test tubes ferric chloride dropper 2 x 50 mL beakers ethanol hot plate Mortar and pestle aspirin tablets 50 mL graduated cylinder Parafilm spec 20 cuvettes Distilled water centigram balance shell vial Filter funnel filter paper stand with iron ring Procedure Day 1 – Synthesis 1. Use a centigram balance to weigh a 50 mL Erlenmeyer flask. Place about 2 g of sylicylic acid in the flask and weigh again. In the fume hood, the instructor will transfer 5.0 mL of acetic anhydride from a buret into the flask. Add 5 drops of 85% phosphoric acid (catalyst) to the flask. 2. Clamp the flask in a beaker of tap water supported on a ring stand over a burner flame. Stir if needed to dissolve the salicylic acid. Heat the water to boiling, and shut off the flame. Keep the flask in the hot water bath for 10 more minutes. 3. While the flask is still in the water bath, slowly add 2 mL of distilled water to the flask to decompose any excess acetic anhydride.