In the lab manual you are required to keep a 2 – 3 mm layer ofacetone and then add water. A student vaporized the acetoneabsolutely and state that he can use the residue for the latermeasurement. What is the biggest defect of doing this comparing tothe correct procedure? How the calculated yield and measuredboiling range will be affected?
Experiment 4: Extraction of an Antibiotic Introduction Theextraction of compounds from plant and animal sources is vitaldirection used by the pharmaceutical industry in search of newmedications. Often the natural products uncovered have undesirableside-effects or lower than desired efficacy. The modification ofthe structures of natural products can lead to improvedpharmokinetics or improved specificity. Extractions are performedby many of us on a daily basis as we brew coffees and teas.Essentially we are using hot water to extract the tasty watersoluble esters and flavors from the solids (and some caffeine).Lichens are a symbiotic relationship between a fungus and an algae.The fungi were originally considered be only useful in theabsorption of water, to the point they were considered almostparasitic. However, it has become clear that the fungus isresponsible for the generation of a very important chemical defenseagent, usnic acid. Several lichens native to New England have beenshown to have antibiotic properties and usnic acid has been shownto be the agent responsible for this biological activity. Lichenshave been used medicinally for thousands of years. There isevidence the Egyptians viewed lichens as medicines. Usnic acid hasbeen found to useful as an antibiotic with activity against severalGram-positive bacteria including skin infections and tuberculosis.There have been reports that usnic acid can cause liverproblems.
Experimental Procedure 1. Weigh 4 grams of lichen and place in a150 ml beaker. 2. Add 50ml of acetone to the 150ml beaker. 3. Stirand crush the lichen in the acetone with a stir-rod or spatula for30 minutes. 4. Remove the pieces of lichen from the acetone byfiltering through a glass funnel with a folded filter paper (15cm)into a 125ml Erlenmeyer flask. 5. Clean the 125ml beaker andtransfer the contents of the Erlenmeyer flask. 6. Add two boilingsticks and place the beaker on a hotplate (in the hood) and warm toboiling (setting #4 is usually sufficient). 6. Evaporate almost allthe acetone. A layer approximately 2-3mm deep at the bottom of thebeaker is all that is required. Some solid may be noted at themeniscus. 22 7. Remove the beaker from the heat and remove theboiling sticks. Return to your bench area. 8. Add 2-4 drops ofwater until a slightly cloudiness is noted. 9. After the flask hascooled on the bench-top for approximately 3 minutes, filter thesmall yellow crystals using a Buchner funnel, a vacuum flask(125ml) and an aspirator to apply a vacuum. Use the illustration onpage 24 as a guide. 10. Weigh the crystals and calculate apercentage of the lichens that is usnic acid. Note the meltingpoint of the crystals. Results and Calculations. 1. Yield should benoted by weighing the crystals formed and comparing to the initialweight of the lichens. 2. Melting range of the usnic acid should benoted. Waste Management The usnic acid generated in this experimentis not regulated as hazardous waste. Acetone is regulated by theEPA as hazardous wastes because they are ignitable below 140 deg F.1. The filter paper with ground lichens, from Step 4 of theexperiment, is non-hazardous and can be disposed of in thetrashcan. 2. The filtrate from step 9 of the experiment containsacetone and is flammable. Dispose of as hazardous waste in thewaste container labeled with the respective chemical contents. 4.The usnic acid crystals are non-hazardous so can discarded intonormal trash. 5. The vacuum flask used for filtration can be washedwith soap and water to remove residue. Any acetone used to rinseshould be discarded of as hazardous waste.
