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Lab Manual- Experiment 5

Lab Manual- Experiment 5 - Experiment 5 IDENTIFICATION OF...

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E x p er i m e n t 5: IDENTIFICATION OF AN UNKNOWN MIXTURE BY TLC AND SEPARATION OF THAT MIXTURE USING ACID-BASE EXTRACTION References: Pavia, Technique 12 (pages 681-702). Read the Essays on Aspirin (p. 53), Analgesics (p. 60), Identification of Drugs (p. 67), Caffeine (p. 73), and any others of interest such as Local Anesthetics (p. 343). In the above reading assignments you must pay special attention to the principles behind the separation techniques we employ (pages 777-819). Also read the sections on extraction (sections 12.1- 12.8) and drying agents (section 12.9). Your lab instructor will demonstrate the use of the separatory funnel. It is also essential to understand the fundamental principles of acidity and basicity, and the application of these principles in organic chemistry. You must spend a substantial amount of time studying your lecture textbook to develop this understanding. Solomons & Fryhle, comes from pages 115-122, 813-818, and 945-949; Wade pages 22-29, 877-882, 940-946. The separation of acids and bases from neutral compounds by extraction is routinely employed in research laboratories. Aspirin (acetylsalicylic acid) readily donates a proton to hydroxide, carbonate, or bicarbonate ion. Its resulting conjugate base (an anion) is more soluble in water solutions of these bases than in common organic solvents. Caffeine is basic and readily accepts a proton in aqueous acid. Its conjugate acid (a caution) is more soluble in water than in the relatively non-polar common organic solvents. Phenacetin is neutral and does not easily accept or donate a proton. All three compounds are pressed together with a starch binder to form APC tablets. Please note that phenacetin has been found to cause kidney damage and is no longer in common use. Your unknown mixture contains TWO of the three compounds, aspirin, phenacetin or caffeine. You will determine which two are present, and then separate the components from each other to obtain pure samples of each. These are industrial chemical (not intended for human consumption). After separating the two compounds you will use thin layer chromatography to test the completeness of your separation. Success in this experiment requires an unusually large amount of planning and careful preparation!! Preliminary Write-up: a) Objectives of the experiment. Be brief b) Table of relevant physical properties and safety data for compounds/solvents in Parts I, II and III. (Toxicities and structures of aspirin, caffeine, phenacetin; boiling and melting points, densities, toxicities, and relative polarity of TLC and extraction solvents).
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