Experiment 1


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EXPERIMENT #1 SEPARATION AND RECOVERY OF ORGANIC COMPOUNDS, THIN LAYER CHROMATOGRAPHY, COLUMN CHROMATOGRAPHY, CRYSTALLIZATION AND MELTING POINTS Overview In the first few weeks of this semester you will be learning a variety of techniques that are routinely used by organic chemists. In the first week, you will separate two organic compounds from a mixture that also contains sand. Once you have recovered the organic compounds, you will need to separate them from each other, and to purify each of them. To accomplish this, you will use thin layer chromatography (TLC) to determine solvents appropriate to separate the components, and then use this information the second week to run a column separation. The third week you will check the purity of the separated compounds by taking melting points and then purify the compounds further by crystallizing each from an appropriate solvent or solvent pair. A brief discussion of most of the techniques is provided, but you are responsible for reading more comprehensive treatments in the laboratory textbooks available in the Science Library. Week 1 Background and Procedure Obtain approximately 3.0 grams (weighed to the nearest 0.1g) of one of the mixtures of sand, 9-fluorene and 9-fluorenone. Place this into a 125 mL Erlenmeyer flask and add about 10 mL of dichloromethane, CH 2 Cl 2 (an older name, still in use, is methylene chloride). Add a magnetic stir bar and heat on a stirrer-hot plate, set as low as possible, under your fume hood . Swirl the flask and note that some of the organic material dissolves. Add dichloromethane, a little at a time, and observe if more solid dissolves. Keep the solution stirring to avoid bumping. Add enough solvent to completely dissolve the organic compounds. The amount of solvent used is not terribly critical at this point because you will be evaporating it after you remove the sand. Filter the solution by gravity, using a fluted filter paper. Fluting filter paper increases the surface area of the paper and allows air to enter the flask to permit rapid pressure equalization. Gravity filtration is used to remove insoluble impurities, in this case, the sand. Save a small amount of the filtrate for thin layer chromatography (just a few drops in a spot plate are sufficient), transfer the rest to an appropriately sized round-bottomed flask, i.e. one that will be no more than half full, and evaporate the filtrate on the rotary evaporator (Rotovap). Transfer the residue from the flask to a storage vial labeled with your name, lab day, and identity of the contents. The next step is to spot your filtrate and authentic samples of fluorene and fluorenone side-by-side on a TLC plate and elute the plate with an available solvent you think should separate them. Thin layer chromatography is a very rapid technique, so if your “educated guess” proves incorrect, you can easily run plates using several different solvents in a short period of time. The following discussion of thin layer chromatography should help to familiarize you with the technique. Chromatography is defined as the
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This note was uploaded on 10/06/2010 for the course ES ES271 taught by Professor Machaut during the Spring '10 term at Colby.

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