Preparing a Prelab Flow Sheet for the Synthesis of (+)-(R)-3-Methyladipic Acid - Prof. Nan, Lab Reports of Organic Chemistry

Download Preparing a Prelab Flow Sheet for the Synthesis of (+)-(R)-3-Methyladipic Acid - Prof. Nan and more Lab Reports Organic Chemistry in PDF only on Docsity! Totah rev. 8/2009 The Prelab Flow Sheet You will be asked to prepare a prelab flow sheet for each synthetic experiment that you do this semester, as well as for several others. In these experiments, the Flow Sheet will replace Section E (Research Plan) of the prelab. The purpose of this flow sheet is to get you to think about the experiment you are doing; not only about the reaction itself, but also the processes involved in the isolation of your pure compound. Believe it or not, there is a reason for every step in an experimental sequence. If you are unsure about the reasons behind a specific step or action described in the laboratory handout, be sure to get help! It is always more satisfying to understand the reasoning behind a set of instructions than to follow them blindly. A sample flow sheet from an experimental procedure that was used previously, Synthesis of (+)-(R)-3-Methyladipic Acid, is included below. Remember, though, that every experiment is different. The flow sheet you submit may not look exactly like the one in the sample! The prelab for a technique experiment will look slightly different than that presented here. An appropriate flow sheet for this type of experiment can be found in Experiment 4 (Figures 1 and 2). Hints: 1. Write a balanced equation for the reaction you will be doing. Be sure to include any by-products of the reaction that will need to be separated later. It is much easier to figure out what is going on if you know what you're trying to do in the first place. 2. Don't go overboard. In most cases, a single page will be sufficient to outline the experimental procedures set forth in the laboratory handout. 3. Check back to your Flow Sheet as you carry our the lab. Sample Procedure: Me O CO2K Me CO2K CO2H Me CO2H 3-methyladipic acid dipotassium salt 3-methyladipic acidpulegone KMnO4 HCl A. Synthesis of (+)-(R)-3-Methyladipic Acid: To a 250mL Erlenmeyer flask containing 40mL of distilled water add 5mL of pulegone. Swirl to mix the components (a two-phase mixture should result), then add 5g of KMnO4. Continue swirling for 10 minutes, then allow the mixture to stand for approximately 2 hours, swirling occasionally. After this time, heat the mixture in a boiling water bath for 10 minutes. CAUTION! The oxidation of pulegone is exothermic. Keep an ice bath handy as the mixture may boil over if it proceeds too quickly. After the heating period, allow the reaction to cool to room temperature, stopper the flask, and store it until the next laboratory period. Totah rev. 8/2009 Test the reaction mixture for the presence of KMnO4. This is done by withdrawing a drop of the mixture on the tip of a stirring rod and touching it to a piece of filter paper. Permanganate, if present, will appear as a purple ring around the brown MnO2 solids. Remaining permanganate should be reduced to MnO2 by adding a small amount of solid sodium bisulfite, and stirring vigorously (Note: an exotherm and some foaming will occur. As such, do this in the hood, and don't add too much bisulfite at once.). Continue adding bisulfite in small amounts until the test for permanganate is negative. Prepare a slurry of 2-3mL of celite in 25mL water and vacuum filter. Continue to apply the vacuum until the celite bed is relatively dry, then discard the water. To remove the fine precipitate of MnO2 solids, filter the reaction mixture through the celite bed in parts. The filtration will proceed much more quickly if the solids are allowed to dry out completely between additions. Wash the filtered solids with three successive 10mL portions of water, gently stirring the MnO2 solids above the celite while they are wet to maximize the surface area. When filtration is complete, the MnO2 solids should be discarded in the Waste Solids bag in the hood. The combined filtrates should be clear and slightly yellow. Transfer them to a 250mL beaker, add 2-3 boiling chips, and concentrate to about 15mL on a hot plate. Cool to room temperature, and, in the hood, acidify with 10mL of concentrated HCl. If at this point solids form, remove them by filtration. Extract the cool aqueous solution with four 15mL portions of dichloromethane (4 x 15mL). Be sure you are aware which layer is the aqueous, and which one is organic. Discard the remaining aqueous layer into the appropriate bottle in the hood. Residual product can later be extracted from this combined aqueous waste. Dry the combined organics over MgSO4, then remove the solids by gravity filtration. Transfer the filtrates to a tared flask, and concentrate. If there is a long wait for the rotary evaporator, add 2-3 boiling chips, and remove the solvent by distillation using a water aspirator. Note that excessive heat is not required, and may cause the material to bump or boil over. Before the concentration is complete, remove the boiling stones so an accurate weight may be obtained on your crude product. Evaporate the remaining solvent on the rotovap or in the hood. CAUTION! There is some indication that CH2Cl2 may be carcinogenic. Once concentration is complete, a thick yellow liquid should remain which may partially solidify on cooling. Recrystallize this product from toluene, using 5mL toluene for every gram of crude product. Collect the resulting crystals of (+)-(R)-3-methyladipic acid by filtration, scraping the solids with a spatula to aid in drying them. Continue to apply the vacuum for some time as toluene is quite difficult to remove. When finished, place the toluene filtrates in the bottle marked Toluene Waste. Here too, residual product can later be isolated. Record the weight of your crystalline product, and obtain a melting point and a solution cell IR (use CH2Cl2 as the solvent). Calculate your % yield based on the amount of pulegone you used. Turn in the remainder of your product to your TA when you submit your laboratory report. Note that a portion of your grade will depend on the product you turn in. Balanced Equation: CO2K CO2K O Me Me CO2H CO2H Me O 2 MnO2+ 2 KMnO4 2 HCl+ 2 KCl+