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 CH2Cl2 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 separation of a mixture of two or more different compounds or ions by distribution between two phases one of which is stationary and one of which is moving The experimental procedure for thin layer chromatography is straightforward and easy however background reading on the theory and technique is important Most of the laboratory manuals in room 142 of the Science Library have sections dealing with chromatography Since Week 2 of this experiment will involve column chromatography you may wish to read about both types in preparation for that lab as well There is an especially nice treatment in Introduction to Organic Laboratory Techniques by Pavia Lampman and Kriz but every laboratory manual will include some treatment of both thin layer and column chromatography In the lab you will find commercially prepared precut thin layer plates of silica gel Be sure to handle them only by the edges or you may find that you inadvertently perform chromatography on your fingerprints Very fine glass capillary tubing will be available for spotting your compounds Up to five fractions can be spotted on a single plate perhaps more when you have mastered the technique Every plate you run must include authentic samples of fluorene and fluorenone so that the Rf values of these compounds can be compared to the Rf values of the spots you find using your experimental compounds During the first week you will also run a very short experiment to familiarize yourself with solvents that are either miscible or immiscible in each other Add about 1 ml of water to a small test tube with a Pasteur pipette Then add 1 ml of an organic solvent hexanes dichloromethane ethanol or acetone and mix Let the test tube sit for a moment and note how many layers are present If there is a single layer the two liquids are miscible but if there are two layers then the liquids are immiscible in each other Repeat the test using water and the remaining three organic solvents For immiscible solvent pairs identify the aqueous and organic layers Record your observations in your notebook in table form as indicated below Solvent Pairs Water Hexanes Water Acetone Water Ethanol Water Dichloromethane if miscible If not go to next column Immiscible Solvent Pair Aqueous Organic Layer Layer Top or Top or Bottom Bottom Top or Top or Bottom Bottom Top or Top or Bottom Bottom Top or Top or Bottom Bottom Prelab Assignment The Merck Index the CRC Handbook of Chemistry and Physics and the Aldrich and Acros chemical catalogs found on the reference shelves of the library will be helpful in answering the first two questions 1 Look up the structures not just the molecular formulas melting points and solubility characteristics of 9H fluorene and 9 fluorenone 2 Look up the density and boiling point of dichloromethane 3 From the laboratory textbooks in room 142 of the Science Library read a treatment of thin layer chromatography In your notebook write an outline describing how to conduct an analysis by thin layer chromatography Make sure to include a procedure for spotting eluting visualization of the plates and calculation of Rf values Thin layer plates are commercially available and will be provided for you so describing plate preparation is not necessary Week 2 Background and Procedure From week 1 you are familiar with the theory and practice of thin layer chromatography A natural extension of that technique is column chromatography which is useful for purifying compounds on a preparative scale